| 0/0 |
2026/05/18 02:20 |
flow |
assessment-security |
54m
Results: map[DenialOfService:true Explanation:Based on the analysis of the bug report and the kernel source code, here is the
assessment of the vulnerability:
### Root Cause Analysis
The bug is a Use-After-Free (UAF) in the Virtual Terminal (VT) keyboard driver
(`drivers/tty/vt/keyboard.c`).
When processing keyboard events, `kbd_keycode()` retrieves the foreground
console's TTY via `vc->port.tty` and passes it to various handlers (like
`fn_hold()` when the Scroll Lock key is pressed, or `tty_chars_in_buffer()` for
repeating keys). However, it does so without taking a reference count
(`tty_kref_get()`) or holding a lock that would prevent the TTY from being
concurrently destroyed.
If an unprivileged user closes all file descriptors associated with the VT,
`tty_release_struct()` is invoked, which eventually schedules
`release_one_tty()` in a workqueue to free the `tty_struct`. If the `tty_struct`
is freed while the keyboard handler is still using it (e.g., while holding
`tty->flow.lock` inside `start_tty()`), a UAF occurs. The KASAN report
specifically catches the UAF during the spinlock unlock path
(`rt_mutex_slowunlock` -> `raw_spin_lock_irqsave`) because the underlying memory
backing the lock was freed while the lock was held.
### Security Impact
* **Exploitable:** **Yes**. This UAF is highly exploitable for local privilege
escalation (LPE). While the `tty_struct` is freed, functions like
`__start_tty()` or `tty_chars_in_buffer()` dereference the `tty->ops` pointer
and perform indirect function calls (e.g., `tty->ops->start(tty)`). An attacker
can spray the `kmalloc-cg-2k` slab cache to reallocate the freed `tty_struct`
with attacker-controlled data, pointing `tty->ops` to a fake `tty_operations`
table. This allows for a direct control-flow hijack to execute arbitrary code
(e.g., a ROP chain) in the kernel context.
* **Denial Of Service:** **Yes**. If not successfully exploited for LPE, the
wild pointers and memory corruption will reliably crash the kernel.
* **Accessible From Unprivileged Processes:** **Yes**. A typical local
unprivileged user logged into a VT can open/close `/dev/tty` to trigger the
allocation and freeing of the `tty_struct`, while concurrently pressing keys
(like Scroll Lock) to hit the race condition.
* **Accessible From User Namespaces:** **Yes**. The bug doesn't strictly require
user namespaces, but a process within a user namespace that has access to a VT
can trigger it just the same.
* **Peripheral Trigger:** **Yes**. A malicious USB device acting as a keyboard
can precisely inject the necessary keystrokes (like Scroll Lock or rapid
repeating keys) to win the race condition against the TTY teardown.
* **VM Guest Trigger:** **Yes**. A user inside a KVM guest can trigger this
using the emulated virtual keyboard.
* **VM Host Trigger in The Confidential Computing Context:** **Yes**. A
malicious hypervisor can inject arbitrary keystrokes via the
paravirtualized/emulated keyboard device into a confidential guest to trigger
the UAF and hijack the guest kernel's control flow.
* **Network / Remote / Filesystem Trigger:** **No**. The bug is tied to the
local VT keyboard input subsystem and cannot be triggered via network packets or
filesystem parsing. Exploitable:true FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:true RemoteTrigger:false Unprivileged:true UserNamespace:true VMGuestTrigger:true VMHostTrigger:true]
|
| 1/1 |
2026/05/18 02:20 |
action |
syz-repro-to-c-repro |
0m
Results:
|
| 2/1 |
2026/05/18 02:20 |
action |
kernel-checkouter |
0m
Results: map[KernelSrc:/app/workdir/cache/src/920996bf9f4bbd5cfc377126ec66e6ea70f54852]
|
| 3/1 |
2026/05/18 02:20 |
action |
kernel-builder |
27m
Results: map[KernelObj:/app/workdir/cache/build/544cf9f3ed93971e668cbc8cdde36a1617595374]
|
| 4/1 |
2026/05/18 02:48 |
action |
codesearch-prepare |
18m
Results: map[Index:codesearch-index]
|
| 5/1 |
2026/05/18 03:06 |
agent |
expert |
8m
Model:
Results: map[DenialOfService:true Exploitable:true FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:true RemoteTrigger:false Unprivileged:true UserNamespace:true VMGuestTrigger:true VMHostTrigger:true]
Instruction:
You are an experienced Linux kernel security engineer. Your task is to analyze given kernel bug report
and determine its security impact based on the following dimensions.
Use the provided tools to examine the source code, check for capability checks (e.g., capable(), ns_capable()),
and understand the nature of the bug. Analyze the given kernel build and configuration.
You can check the kernel config by grepping ".config" file; you can check kernel cmdline by greeping
".config" file for "CONFIG_CMDLINE=". Assume sysctl parameters have default values.
But analyze for the corresponding production build w/o debugging tools enabled (like KASAN, KMSAN, UBSAN).
Don't make assumptions; verify them with source code access. Try different strategies when analyzing the bug:
- think of ways in which the vulnerable code is unreachable
- or the other way around: try to come up with different ideas of how an unprivileged user can reach the bug
If still unsure err on the side of the bug being non-exploitable/not-accessible.
In the final reply, provide a reasoning for your assessment.
Analysis dimensions:
* Exploitable:
Determine if the bug can result in memory corruption or elevated privileges.
Memory safety issues are almost always exploitable (KASAN or UBSAN reports for use-after-free, out-of-bounds;
refcounting issues, corrupted lists, etc). When kernel is crashing on a completly wild pointer access
(e.g. user-space address, or non-canonical address, but not on NULL or address corresponding to KASAN shadow
for NULL address), including both data accesses and control tranfers, that's also usually implies possibility
of exploitation. Such reports usually say "unable to handle kernel paging request".
Uses of uninitialized values detected by KMSAN may be exploitable b/c attacker frequently can affect uninit
values with spraying techniques. However, for these exploitabability depends on how exactly the uninit value
is used in the code, and what it affects.
Think of what happens after the bug is triggered. Some bugs cause kernel panic and halt execution,
they are harder to exploit. For example, BUG reports halts the kernel. However, WARNING reports don't halt
execution in production builds. Debug bug detection tools (like KASAN, KMSAN, KCSAN, UBSAN) are also not enabled
in production builds, so attacker can freely exploit these bugs w/o being detected by these tools.
If you see an integer overflow, think how the overflowed value used later (if it's used as allocation size,
or an array index). If you see an out-of-bounds read, think if it's followed by an out-of-bounds write as well.
Some KCSAN data-races may be exploitable by skilled attackers as well. Think what data structures got corrupted
as the result of data races and how. However, note that kernel has lots of "benign" data races that don't lead
to any runtime misbehavior at all.
* Denial Of Service:
Determine if the bug can result in denial-of-service. Most bugs can, since they cause system crash,
hangs, deadlocks, or resource leaks. This is mostly applicable to WARNING bugs that won't cause system crash
in production. For these think what will be consequences of the violation of the kernel assumptions flagged
by the WARNING. In some cases the unexpected condition is also properly handled by the normal control flow
(e.g. with "if (WARN_ON(...))"), these won't cause denial-of-service. If the condition is not handled,
then it may or may not cause denial-of-service.
* Accessible From Unprivileged Processes:
Determine if the bug can be reached from a typical (non-root) user process that does NOT have any special capabilities
(like CAP_SYS_ADMIN, CAP_NET_ADMIN, CAP_NET_RAW, CAP_PERFMON) or access to device nodes restricted to root.
Assume that unprivileged_bpf_disabled=1, that is eBPF loading is not accessible. However, cBPF (classical BPF)
is still accessible to non-root processes.
Assume that user namespaces are not accessible, that is, the process cannot get the mentioned capabilities even
within a new user namespace (checked by ns_capable() function in the kernel sources).
* Accessible From User Namespaces:
Determine if the bug can be reached within a user-namespace where the process has all capabilities
(including CAP_SYS_ADMIN, CAP_NET_ADMIN, CAP_NET_RAW, CAP_PERFMON). Such capabilities are checked with ns_capable()
function in the kernel sources.
* VM Guest Trigger:
Determine if the bug can be triggered from the context of a typical KVM guest (e.g., set up by a QEMU VMM).
Consider accesses to standard Linux host paravirtualized features (virtio-blk, virtio-net, etc.),
and handling of VM exits in the KVM code.
* VM Host Trigger in The Confidetial Computing Context:
Determine if the bug can be triggered in a confidential computing guest kernel from the context of a KVM host.
Consider access to standard Linux guest paravirtualized features (virtio-blk, virtio-net, etc.).
* Ethernet Network Trigger:
Determine if the bug can be triggered by processing ingress network Ethernet traffic, either directly (network stack)
or via drivers exposed to network data.
* Other Remote Trigger:
Determine if the bug can be triggered by processing remote traffic other than Ethernet (Wifi, Bluetooth, NFC, etc).
* Peripheral Trigger:
Determine if the bug can be triggered via an untrusted peripheral device that can be physically plugged
into a system, such as a USB device or a niche hardware driver handling external hardware inputs.
This is particularly important for mobile and desktop environments where users can plug in unknown devices.
* Malicious Filesystem Trigger:
Determine if the bug can be triggered by the kernel mounting and parsing a malicious filesystem image.
This is highly critical for Desktop and Mobile environments where external media or downloaded images
might be auto-mounted.
Prefer calling several tools at the same time to save round-trips.
Use set-results tool to provide results of the analysis.
It must be called exactly once before the final reply.
Ignore results of this tool.
Prompt:
The kernel bug report is:
==================================================================
BUG: KASAN: slab-use-after-free in __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:132 [inline]
BUG: KASAN: slab-use-after-free in _raw_spin_lock_irqsave+0x40/0x60 kernel/locking/spinlock.c:166
Read of size 1 at addr ffff888051204418 by task syz.6.4599/21087
CPU: 0 UID: 0 PID: 21087 Comm: syz.6.4599 Tainted: G L syzkaller #0 PREEMPT_{RT,(full)}
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
print_address_description+0x55/0x1e0 mm/kasan/report.c:378
print_report+0x58/0x70 mm/kasan/report.c:482
kasan_report+0x117/0x150 mm/kasan/report.c:595
__kasan_check_byte+0x2a/0x40 mm/kasan/common.c:574
kasan_check_byte include/linux/kasan.h:402 [inline]
lock_acquire+0x84/0x350 kernel/locking/lockdep.c:5842
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:132 [inline]
_raw_spin_lock_irqsave+0x40/0x60 kernel/locking/spinlock.c:166
rt_mutex_slowunlock+0xbf/0x8b0 kernel/locking/rtmutex.c:1426
kbd_keycode drivers/tty/vt/keyboard.c:1565 [inline]
kbd_event+0x2f91/0x42f0 drivers/tty/vt/keyboard.c:1583
input_handle_events_default+0xd4/0x1a0 drivers/input/input.c:2558
input_pass_values+0x288/0x890 drivers/input/input.c:128
input_event_dispose+0x330/0x6b0 drivers/input/input.c:342
input_inject_event+0x1d7/0x320 drivers/input/input.c:424
evdev_write+0x328/0x4c0 drivers/input/evdev.c:528
vfs_write+0x2a3/0xba0 fs/read_write.c:686
ksys_write+0x156/0x270 fs/read_write.c:740
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f1d8c46ce59
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f1d8a6be028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f1d8c6e5fa0 RCX: 00007f1d8c46ce59
RDX: 0000000000002250 RSI: 0000200000000040 RDI: 0000000000000009
RBP: 00007f1d8c502d6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f1d8c6e6038 R14: 00007f1d8c6e5fa0 R15: 00007ffec9f38108
</TASK>
Allocated by task 21087:
kasan_save_stack mm/kasan/common.c:57 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
__kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415
kasan_kmalloc include/linux/kasan.h:263 [inline]
__kmalloc_cache_noprof+0x3a6/0x690 mm/slub.c:5419
kmalloc_noprof include/linux/slab.h:950 [inline]
kzalloc_noprof include/linux/slab.h:1188 [inline]
alloc_tty_struct+0xa6/0x7b0 drivers/tty/tty_io.c:3102
tty_init_dev+0x59/0x4d0 drivers/tty/tty_io.c:1400
tty_open_by_driver drivers/tty/tty_io.c:2073 [inline]
tty_open+0x86e/0xd80 drivers/tty/tty_io.c:2120
chrdev_open+0x4d0/0x5f0 fs/char_dev.c:411
do_dentry_open+0x83d/0x13e0 fs/open.c:947
vfs_open+0x3b/0x350 fs/open.c:1079
do_open fs/namei.c:4699 [inline]
path_openat+0x2e43/0x38a0 fs/namei.c:4858
do_file_open+0x23e/0x4a0 fs/namei.c:4887
do_sys_openat2+0x113/0x200 fs/open.c:1364
do_sys_open fs/open.c:1370 [inline]
__do_sys_openat fs/open.c:1386 [inline]
__se_sys_openat fs/open.c:1381 [inline]
__x64_sys_openat+0x138/0x170 fs/open.c:1381
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
Freed by task 16547:
kasan_save_stack mm/kasan/common.c:57 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
poison_slab_object mm/kasan/common.c:253 [inline]
__kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
kasan_slab_free include/linux/kasan.h:235 [inline]
slab_free_hook mm/slub.c:2689 [inline]
slab_free mm/slub.c:6250 [inline]
kfree+0x1c5/0x6c0 mm/slub.c:6565
process_one_work kernel/workqueue.c:3314 [inline]
process_scheduled_works+0xb5d/0x1860 kernel/workqueue.c:3397
worker_thread+0xa53/0xfc0 kernel/workqueue.c:3478
kthread+0x388/0x470 kernel/kthread.c:436
ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
Last potentially related work creation:
kasan_save_stack+0x3e/0x60 mm/kasan/common.c:57
kasan_record_aux_stack+0xbd/0xd0 mm/kasan/generic.c:556
insert_work+0x3d/0x330 kernel/workqueue.c:2226
__queue_work+0xd1d/0x1090 kernel/workqueue.c:2393
queue_work_on+0x106/0x1d0 kernel/workqueue.c:2444
tty_release_struct+0xb8/0xd0 drivers/tty/tty_io.c:1692
tty_release+0xcb6/0x1710 drivers/tty/tty_io.c:1852
__fput+0x461/0xa70 fs/file_table.c:510
task_work_run+0x1d9/0x270 kernel/task_work.c:233
resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
__exit_to_user_mode_loop kernel/entry/common.c:67 [inline]
exit_to_user_mode_loop+0xf3/0x4d0 kernel/entry/common.c:98
__exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline]
syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:238 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:318 [inline]
do_syscall_64+0x33e/0xf80 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f
The buggy address belongs to the object at ffff888051204000
which belongs to the cache kmalloc-cg-2k of size 2048
The buggy address is located 1048 bytes inside of
freed 2048-byte region [ffff888051204000, ffff888051204800)
The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff888051206000 pfn:0x51200
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
memcg:ffff888051200811
flags: 0x80000000000240(workingset|head|node=0|zone=1)
page_type: f5(slab)
raw: 0080000000000240 ffff88801a0293c0 ffff88801a02a388 ffffea00013fc210
raw: ffff888051206000 0000100000080006 00000000f5000000 ffff888051200811
head: 0080000000000240 ffff88801a0293c0 ffff88801a02a388 ffffea00013fc210
head: ffff888051206000 0000100000080006 00000000f5000000 ffff888051200811
head: 0080000000000003 fffffffffffffe01 00000000ffffffff 00000000ffffffff
head: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000008
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 17598, tgid 17598 (syz-executor), ts 1352112276231, free_ts 1351738438926
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x231/0x280 mm/page_alloc.c:1858
prep_new_page mm/page_alloc.c:1866 [inline]
get_page_from_freelist+0x27c8/0x2840 mm/page_alloc.c:3946
__alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5226
alloc_slab_page mm/slub.c:3278 [inline]
allocate_slab+0x77/0x660 mm/slub.c:3467
new_slab mm/slub.c:3525 [inline]
refill_objects+0x33c/0x3d0 mm/slub.c:7271
refill_sheaf mm/slub.c:2816 [inline]
__pcs_replace_empty_main+0x373/0x720 mm/slub.c:4651
alloc_from_pcs mm/slub.c:4749 [inline]
slab_alloc_node mm/slub.c:4883 [inline]
__do_kmalloc_node mm/slub.c:5294 [inline]
__kmalloc_node_track_caller_noprof+0x60b/0x7e0 mm/slub.c:5407
kmemdup_noprof+0x2b/0x70 mm/util.c:138
kmemdup_noprof include/linux/fortify-string.h:763 [inline]
neigh_sysctl_register+0xae/0xa90 net/core/neighbour.c:3861
addrconf_sysctl_register+0xb3/0x1c0 net/ipv6/addrconf.c:7379
ipv6_add_dev+0xd64/0x1400 net/ipv6/addrconf.c:460
addrconf_notify+0x771/0x1050 net/ipv6/addrconf.c:3662
notifier_call_chain+0x1ad/0x3d0 kernel/notifier.c:85
call_netdevice_notifiers_extack net/core/dev.c:2287 [inline]
call_netdevice_notifiers net/core/dev.c:2301 [inline]
register_netdevice+0x18d5/0x1ed0 net/core/dev.c:11461
veth_newlink+0x67b/0xb70 drivers/net/veth.c:1890
rtnl_newlink_create+0x329/0xb70 net/core/rtnetlink.c:3864
page last free pid 5582 tgid 5582 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
__free_pages_prepare mm/page_alloc.c:1402 [inline]
__free_frozen_pages+0xfa6/0x10f0 mm/page_alloc.c:2943
__slab_free+0x252/0x2a0 mm/slub.c:5612
qlink_free mm/kasan/quarantine.c:163 [inline]
qlist_free_all+0x99/0x100 mm/kasan/quarantine.c:179
kasan_quarantine_reduce+0x148/0x160 mm/kasan/quarantine.c:286
__kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:350
kasan_slab_alloc include/linux/kasan.h:253 [inline]
slab_post_alloc_hook mm/slub.c:4569 [inline]
slab_alloc_node mm/slub.c:4898 [inline]
kmem_cache_alloc_node_noprof+0x22a/0x6e0 mm/slub.c:4950
__alloc_skb+0x1d0/0x7d0 net/core/skbuff.c:702
alloc_skb_fclone include/linux/skbuff.h:1433 [inline]
tcp_stream_alloc_skb+0x3f/0x5c0 net/ipv4/tcp.c:935
tcp_sendmsg_locked+0x134b/0x5370 net/ipv4/tcp.c:1260
tcp_sendmsg+0x2f/0x50 net/ipv4/tcp.c:1455
sock_sendmsg_nosec net/socket.c:787 [inline]
__sock_sendmsg net/socket.c:802 [inline]
sock_write_iter+0x40c/0x4f0 net/socket.c:1254
new_sync_write fs/read_write.c:595 [inline]
vfs_write+0x629/0xba0 fs/read_write.c:688
ksys_write+0x156/0x270 fs/read_write.c:740
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
Memory state around the buggy address:
ffff888051204300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888051204380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888051204400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff888051204480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888051204500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
Reply: Based on the analysis of the bug report and the kernel source code, here is the assessment of the vulnerability:
### Root Cause Analysis
The bug is a Use-After-Free (UAF) in the Virtual Terminal (VT) keyboard driver (`drivers/tty/vt/keyboard.c`).
When processing keyboard events, `kbd_keycode()` retrieves the foreground console's TTY via `vc->port.tty` and passes it to various handlers (like `fn_hold()` when the Scroll Lock key is pressed, or `tty_chars_in_buffer()` for repeating keys). However, it does so without taking a reference count (`tty_kref_get()`) or holding a lock that would prevent the TTY from being concurrently destroyed.
If an unprivileged user closes all file descriptors associated with the VT, `tty_release_struct()` is invoked, which eventually schedules `release_one_tty()` in a workqueue to free the `tty_struct`. If the `tty_struct` is freed while the keyboard handler is still using it (e.g., while holding `tty->flow.lock` inside `start_tty()`), a UAF occurs. The KASAN report specifically catches the UAF during the spinlock unlock path (`rt_mutex_slowunlock` -> `raw_spin_lock_irqsave`) because the underlying memory backing the lock was freed while the lock was held.
### Security Impact
* **Exploitable:** **Yes**. This UAF is highly exploitable for local privilege escalation (LPE). While the `tty_struct` is freed, functions like `__start_tty()` or `tty_chars_in_buffer()` dereference the `tty->ops` pointer and perform indirect function calls (e.g., `tty->ops->start(tty)`). An attacker can spray the `kmalloc-cg-2k` slab cache to reallocate the freed `tty_struct` with attacker-controlled data, pointing `tty->ops` to a fake `tty_operations` table. This allows for a direct control-flow hijack to execute arbitrary code (e.g., a ROP chain) in the kernel context.
* **Denial Of Service:** **Yes**. If not successfully exploited for LPE, the wild pointers and memory corruption will reliably crash the kernel.
* **Accessible From Unprivileged Processes:** **Yes**. A typical local unprivileged user logged into a VT can open/close `/dev/tty` to trigger the allocation and freeing of the `tty_struct`, while concurrently pressing keys (like Scroll Lock) to hit the race condition.
* **Accessible From User Namespaces:** **Yes**. The bug doesn't strictly require user namespaces, but a process within a user namespace that has access to a VT can trigger it just the same.
* **Peripheral Trigger:** **Yes**. A malicious USB device acting as a keyboard can precisely inject the necessary keystrokes (like Scroll Lock or rapid repeating keys) to win the race condition against the TTY teardown.
* **VM Guest Trigger:** **Yes**. A user inside a KVM guest can trigger this using the emulated virtual keyboard.
* **VM Host Trigger in The Confidential Computing Context:** **Yes**. A malicious hypervisor can inject arbitrary keystrokes via the paravirtualized/emulated keyboard device into a confidential guest to trigger the UAF and hijack the guest kernel's control flow.
* **Network / Remote / Filesystem Trigger:** **No**. The bug is tied to the local VT keyboard input subsystem and cannot be triggered via network packets or filesystem parsing.
|
| 6/2 |
2026/05/18 03:06 |
llm |
expert |
0m
Model:
Tokens:
input: 9730
output: 41
thoughts: 572
Thoughts: **Analyzing a KASAN Slab-Use-After-Free Report**
Alright, I've got a KASAN slab-use-after-free report to dive into. The buggy address is `ffff888051204418`, and it's residing within a freed 2048-byte region. The object in question was initially allocated by `alloc_tty_struct` in `drivers/tty/tty_io.c` at line 3102. It seems it got freed later by `tty_release_struct`, which is triggered at line 1692 in the same file, `drivers/tty/tty_io.c`, and this happens through `task_work_run`. That's where it got freed, but we are looking into where it's being used after it's freed.
Now, the use-after-free (UAF) read occurs within `_raw_spin_lock_irqsave`. Tracing back, this function is called from `rt_mutex_slowunlock`, which is, interestingly, called by `kbd_keycode`. From there, it goes up to `kbd_event` and eventually to `input_handle_events_default`. That's a curious callstack.
Let's pull up the stack trace for the UAF and analyze it again:
```
lock_acquire+0x84/0x350 kernel/locking/lockdep.c:5842
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:132 [inline]
_raw_spin_lock_irqsave+0x40/0x60 kernel/locking/spinlock.c:166
rt_mutex_slowunlock+0xbf/0x8b0 kernel/locking/rtmutex.c:1426
kbd_keycode drivers/tty/vt/keyboard.c:1565 [inline]
kbd_event+0x2f91/0x42f0 drivers/tty/vt/keyboard.c:1583
input_handle_events_default+0xd4/0x1a0 drivers/input/input.c:2558
input_pass_values+0x288/0x890 drivers/input/input.c:128
input_event_dispose+0x330/0x6b0 drivers/input/input.c:342
input_inject_event+0x1d7/0x320 drivers/input/input.c:424
evdev_write+0x328/0x4c0 drivers/input/evdev.c:528
```
`rt_mutex_slowunlock`? That seems a bit off, I need to double-check that part. I am pretty sure `kbd_keycode` doesn't directly call that. It likely involves a spinlock like `spin_lock_irqsave(&kbd_event_lock, flags);` or something similar, and I need to look into `drivers/tty/vt/keyboard.c` at the `kbd_keycode` function to confirm this, so let's get that up.
|
| 7/2 |
2026/05/18 03:06 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/tty/vt/keyboard.c IncludeLines:true Name:kbd_keycode]
Results: map[SourceCode:1423: static void kbd_keycode(unsigned int keycode, int down, bool hw_raw)
1424: {
1425: struct vc_data *vc = vc_cons[fg_console].d;
1426: unsigned short keysym, *key_map;
1427: unsigned char type;
1428: bool raw_mode;
1429: struct tty_struct *tty;
1430: int shift_final;
1431: struct keyboard_notifier_param param = { .vc = vc, .value = keycode, .down = down };
1432: int rc;
1433:
1434: tty = vc->port.tty;
1435:
1436: if (tty && (!tty->driver_data)) {
1437: /* No driver data? Strange. Okay we fix it then. */
1438: tty->driver_data = vc;
1439: }
1440:
1441: kbd = &kbd_table[vc->vc_num];
1442:
1443: #ifdef CONFIG_SPARC
1444: if (keycode == KEY_STOP)
1445: sparc_l1_a_state = down;
1446: #endif
1447:
1448: rep = (down == 2);
1449:
1450: raw_mode = (kbd->kbdmode == VC_RAW);
1451: if (raw_mode && !hw_raw)
1452: if (emulate_raw(vc, keycode, !down << 7))
1453: if (keycode < BTN_MISC && printk_ratelimit())
1454: pr_warn("can't emulate rawmode for keycode %d\n",
1455: keycode);
1456:
1457: #ifdef CONFIG_SPARC
1458: if (keycode == KEY_A && sparc_l1_a_state) {
1459: sparc_l1_a_state = false;
1460: sun_do_break();
1461: }
1462: #endif
1463:
1464: if (kbd->kbdmode == VC_MEDIUMRAW) {
1465: /*
1466: * This is extended medium raw mode, with keys above 127
1467: * encoded as 0, high 7 bits, low 7 bits, with the 0 bearing
1468: * the 'up' flag if needed. 0 is reserved, so this shouldn't
1469: * interfere with anything else. The two bytes after 0 will
1470: * always have the up flag set not to interfere with older
1471: * applications. This allows for 16384 different keycodes,
1472: * which should be enough.
1473: */
1474: if (keycode < 128) {
1475: put_queue(vc, keycode | (!down << 7));
1476: } else {
1477: put_queue(vc, !down << 7);
1478: put_queue(vc, (keycode >> 7) | BIT(7));
1479: put_queue(vc, keycode | BIT(7));
1480: }
1481: raw_mode = true;
1482: }
1483:
1484: assign_bit(keycode, key_down, down);
1485:
1486: if (rep &&
1487: (!vc_kbd_mode(kbd, VC_REPEAT) ||
1488: (tty && !L_ECHO(tty) && tty_chars_in_buffer(tty)))) {
1489: /*
1490: * Don't repeat a key if the input buffers are not empty and the
1491: * characters get aren't echoed locally. This makes key repeat
1492: * usable with slow applications and under heavy loads.
1493: */
1494: return;
1495: }
1496:
1497: param.shift = shift_final = (shift_state | kbd->slockstate) ^ kbd->lockstate;
1498: param.ledstate = kbd->ledflagstate;
1499: key_map = key_maps[shift_final];
1500:
1501: /*
1502: * Fall back to the plain map if modifiers are active, the modifier-
1503: * specific map is missing or has no entry, and the plain map has a
1504: * modifier-aware key type (KT_CUR or KT_CSI). These handlers encode
1505: * the modifier state into the emitted escape sequence.
1506: */
1507: if (shift_final && keycode < NR_KEYS &&
1508: (!key_map || key_map[keycode] == K_HOLE) && key_maps[0]) {
1509: unsigned short plain = key_maps[0][keycode];
1510: unsigned char type = KTYP(plain);
1511:
1512: if (type >= 0xf0 && (type - 0xf0 == KT_CUR || type - 0xf0 == KT_CSI))
1513: key_map = key_maps[0];
1514: }
1515:
1516: rc = atomic_notifier_call_chain(&keyboard_notifier_list,
1517: KBD_KEYCODE, ¶m);
1518: if (rc == NOTIFY_STOP || !key_map) {
1519: atomic_notifier_call_chain(&keyboard_notifier_list,
1520: KBD_UNBOUND_KEYCODE, ¶m);
1521: do_compute_shiftstate();
1522: kbd->slockstate = 0;
1523: return;
1524: }
1525:
1526: if (keycode < NR_KEYS)
1527: keysym = key_map[keycode];
1528: else if (keycode >= KEY_BRL_DOT1 && keycode <= KEY_BRL_DOT8)
1529: keysym = U(K(KT_BRL, keycode - KEY_BRL_DOT1 + 1));
1530: else
1531: return;
1532:
1533: type = KTYP(keysym);
1534:
1535: if (type < 0xf0) {
1536: param.value = keysym;
1537: rc = atomic_notifier_call_chain(&keyboard_notifier_list,
1538: KBD_UNICODE, ¶m);
1539: if (rc != NOTIFY_STOP)
1540: if (down && !(raw_mode || kbd->kbdmode == VC_OFF))
1541: k_unicode(vc, keysym, !down);
1542: return;
1543: }
1544:
1545: type -= 0xf0;
1546:
1547: if (type == KT_LETTER) {
1548: type = KT_LATIN;
1549: if (vc_kbd_led(kbd, VC_CAPSLOCK)) {
1550: key_map = key_maps[shift_final ^ BIT(KG_SHIFT)];
1551: if (key_map)
1552: keysym = key_map[keycode];
1553: }
1554: }
1555:
1556: param.value = keysym;
1557: rc = atomic_notifier_call_chain(&keyboard_notifier_list,
1558: KBD_KEYSYM, ¶m);
1559: if (rc == NOTIFY_STOP)
1560: return;
1561:
1562: if ((raw_mode || kbd->kbdmode == VC_OFF) && type != KT_SPEC && type != KT_SHIFT)
1563: return;
1564:
1565: (*k_handler[type])(vc, KVAL(keysym), !down);
1566:
1567: param.ledstate = kbd->ledflagstate;
1568: atomic_notifier_call_chain(&keyboard_notifier_list, KBD_POST_KEYSYM, ¶m);
1569:
1570: if (type != KT_SLOCK)
1571: kbd->slockstate = 0;
1572: }
SourceFile:drivers/tty/vt/keyboard.c]
|
| 8/2 |
2026/05/18 03:06 |
llm |
expert |
0m
Model:
Tokens:
input: 13451
output: 45
thoughts: 90
Thoughts: Okay, here's my breakdown of what's going on, thinking it through from a debugging perspective:
**Debugging a Potential Use-After-Free in the Kernel**
Alright, I'm tracking down this UAF, and the kernel log points to `rt_mutex_slowunlock`. That's the function that's being hit. Now, I have to remember the call chain. Wait, hang on... `kbd_keycode` doesn't *directly* call `rt_mutex_slowunlock`, that doesn't feel quite right. Let me look at the code again. It's likely something triggered *by* `kbd_keycode` that is causing the eventual unlock that is the problem. Aha! `kbd_keycode` calls `atomic_notifier_call_chain`, `put_queue`, or `tty_chars_in_buffer`. It's one of *those* functions that's the real culprit. Let's see... since I am looking for a race with a terminal, let's start by looking at `tty_chars_in_buffer(tty)`. It is most likely to be interacting with a mutex. Let's see how that one is handling its lock.
|
| 9/2 |
2026/05/18 03:06 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/tty/tty_io.c IncludeLines:true Name:tty_chars_in_buffer]
Results: map[SourceCode: 41: /**
42: * tty_chars_in_buffer - characters pending
43: * @tty: terminal
44: *
45: * Returns: the number of bytes of data in the device private output queue. If
46: * no private method is supplied there is assumed to be no queue on the device.
47: */
48: unsigned int tty_chars_in_buffer(struct tty_struct *tty)
49: {
50: if (tty->ops->chars_in_buffer)
51: return tty->ops->chars_in_buffer(tty);
52: return 0;
53: }
SourceFile:drivers/tty/tty_ioctl.c]
|
| 10/2 |
2026/05/18 03:06 |
llm |
expert |
0m
Model:
Tokens:
input: 14057
output: 17
thoughts: 197
Thoughts: **Debugging a Kernel Stack Trace**
Okay, so I'm looking at this stack trace and trying to understand what's going on. First, I was a little confused about `tty_chars_in_buffer`, thought it might be defined inline or something, but no, it's actually in `drivers/tty/tty_ioctl.c`. That's good to know. But, hold on a second... the stack trace shows `rt_mutex_slowunlock` and then calls into `kbd_keycode` in `drivers/tty/vt/keyboard.c`. Line number 1565 in there, specifically. Let me double-check that file.
Alright, I pulled up `drivers/tty/vt/keyboard.c`, and, hmm, the function `kbd_keycode` actually *ends* at line 1572. That's odd. Seems the stack trace is pointing to somewhere within that function's scope. I'll take a closer look around line 1565 in `kbd_keycode`, see what it's doing there, and that should clarify how this relates to the `rt_mutex_slowunlock` call and the overall context of what's happening.
|
| 11/2 |
2026/05/18 03:07 |
tool |
grepper |
0m
Args: map[Expression:kbd_keycode]
Results: map[Output:Documentation/input/notifier.rst=5=One can use register_keyboard_notifier to get called back on keyboard
Documentation/input/notifier.rst:6:events (see kbd_keycode() function for details). The passed structure is
Documentation/input/notifier.rst-7-keyboard_notifier_param (see <linux/keyboard.h>):
--
Documentation/input/notifier.rst=29=In a rough C snippet, we have::
Documentation/input/notifier.rst-30-
Documentation/input/notifier.rst:31: kbd_keycode(keycode) {
Documentation/input/notifier.rst-32- ...
--
drivers/hid/usbhid/usbkbd.c=33=MODULE_LICENSE("GPL");
drivers/hid/usbhid/usbkbd.c-34-
drivers/hid/usbhid/usbkbd.c:35:static const unsigned char usb_kbd_keycode[256] = {
drivers/hid/usbhid/usbkbd.c-36- 0, 0, 0, 0, 30, 48, 46, 32, 18, 33, 34, 35, 23, 36, 37, 38,
--
drivers/hid/usbhid/usbkbd.c=100=static void usb_kbd_irq(struct urb *urb)
--
drivers/hid/usbhid/usbkbd.c-117- for (i = 0; i < 8; i++)
drivers/hid/usbhid/usbkbd.c:118: input_report_key(kbd->dev, usb_kbd_keycode[i + 224], (kbd->new[0] >> i) & 1);
drivers/hid/usbhid/usbkbd.c-119-
--
drivers/hid/usbhid/usbkbd.c-122- if (kbd->old[i] > 3 && memscan(kbd->new + 2, kbd->old[i], 6) == kbd->new + 8) {
drivers/hid/usbhid/usbkbd.c:123: if (usb_kbd_keycode[kbd->old[i]])
drivers/hid/usbhid/usbkbd.c:124: input_report_key(kbd->dev, usb_kbd_keycode[kbd->old[i]], 0);
drivers/hid/usbhid/usbkbd.c-125- else
--
drivers/hid/usbhid/usbkbd.c-131- if (kbd->new[i] > 3 && memscan(kbd->old + 2, kbd->new[i], 6) == kbd->old + 8) {
drivers/hid/usbhid/usbkbd.c:132: if (usb_kbd_keycode[kbd->new[i]])
drivers/hid/usbhid/usbkbd.c:133: input_report_key(kbd->dev, usb_kbd_keycode[kbd->new[i]], 1);
drivers/hid/usbhid/usbkbd.c-134- else
--
drivers/hid/usbhid/usbkbd.c=261=static int usb_kbd_probe(struct usb_interface *iface,
--
drivers/hid/usbhid/usbkbd.c-327- for (i = 0; i < 255; i++)
drivers/hid/usbhid/usbkbd.c:328: set_bit(usb_kbd_keycode[i], input_dev->keybit);
drivers/hid/usbhid/usbkbd.c-329- clear_bit(0, input_dev->keybit);
--
drivers/input/keyboard/amikbd.c=27=MODULE_LICENSE("GPL");
--
drivers/input/keyboard/amikbd.c-29-#ifdef CONFIG_VT
drivers/input/keyboard/amikbd.c:30:static unsigned char amikbd_keycode[0x78] __initdata = {
drivers/input/keyboard/amikbd.c-31- [0] = KEY_GRAVE,
--
drivers/input/keyboard/amikbd.c=129=static void __init amikbd_init_console_keymaps(void)
--
drivers/input/keyboard/amikbd.c-139- for (j = 0; j < 0x78; j++) {
drivers/input/keyboard/amikbd.c:140: if (!amikbd_keycode[j])
drivers/input/keyboard/amikbd.c-141- continue;
drivers/input/keyboard/amikbd.c:142: temp_map[j] = key_maps[i][amikbd_keycode[j]];
drivers/input/keyboard/amikbd.c-143- }
--
drivers/input/keyboard/atakbd.c=37=MODULE_LICENSE("GPL");
--
drivers/input/keyboard/atakbd.c-62-
drivers/input/keyboard/atakbd.c:63:static unsigned char atakbd_keycode[0x73] = { /* American layout */
drivers/input/keyboard/atakbd.c-64- [1] = KEY_ESC,
--
drivers/input/keyboard/atakbd.c=164=static void atakbd_interrupt(unsigned char scancode, char down)
--
drivers/input/keyboard/atakbd.c-170-
drivers/input/keyboard/atakbd.c:171: scancode = atakbd_keycode[scancode];
drivers/input/keyboard/atakbd.c-172-
--
drivers/input/keyboard/atakbd.c=181=static int __init atakbd_init(void)
--
drivers/input/keyboard/atakbd.c-204- atakbd_dev->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_REP);
drivers/input/keyboard/atakbd.c:205: atakbd_dev->keycode = atakbd_keycode;
drivers/input/keyboard/atakbd.c-206- atakbd_dev->keycodesize = sizeof(unsigned char);
drivers/input/keyboard/atakbd.c:207: atakbd_dev->keycodemax = ARRAY_SIZE(atakbd_keycode);
drivers/input/keyboard/atakbd.c-208-
drivers/input/keyboard/atakbd.c-209- for (i = 1; i < 0x72; i++) {
drivers/input/keyboard/atakbd.c:210: set_bit(atakbd_keycode[i], atakbd_dev->keybit);
drivers/input/keyboard/atakbd.c-211- }
--
drivers/input/keyboard/lkkbd.c=85=MODULE_PARM_DESC(lk201_compose_is_alt,
--
drivers/input/keyboard/lkkbd.c-139-
drivers/input/keyboard/lkkbd.c:140:static unsigned short lkkbd_keycode[LK_NUM_KEYCODES] = {
drivers/input/keyboard/lkkbd.c-141- [0x56] = KEY_F1,
--
drivers/input/keyboard/lkkbd.c=423=static irqreturn_t lkkbd_interrupt(struct serio *serio,
--
drivers/input/keyboard/lkkbd.c-444- case LK_ALL_KEYS_UP:
drivers/input/keyboard/lkkbd.c:445: for (i = 0; i < ARRAY_SIZE(lkkbd_keycode); i++)
drivers/input/keyboard/lkkbd.c-446- input_report_key(input_dev, lk->keycode[i], 0);
--
drivers/input/keyboard/lkkbd.c=604=static int lkkbd_connect(struct serio *serio, struct serio_driver *drv)
--
drivers/input/keyboard/lkkbd.c-623- lk->ctrlclick_volume = ctrlclick_volume;
drivers/input/keyboard/lkkbd.c:624: memcpy(lk->keycode, lkkbd_keycode, sizeof(lk->keycode));
drivers/input/keyboard/lkkbd.c-625-
--
drivers/input/keyboard/locomokbd.c=33=static const unsigned char
drivers/input/keyboard/locomokbd.c:34:locomokbd_keycode[LOCOMOKBD_NUMKEYS] = {
drivers/input/keyboard/locomokbd.c-35- 0, KEY_ESC, KEY_ACTIVITY, 0, 0, 0, 0, 0, 0, 0, /* 0 - 9 */
--
drivers/input/keyboard/locomokbd.c=221=static int locomokbd_probe(struct locomo_dev *dev)
--
drivers/input/keyboard/locomokbd.c-268- input_dev->keycode = locomokbd->keycode;
drivers/input/keyboard/locomokbd.c:269: input_dev->keycodesize = sizeof(locomokbd_keycode[0]);
drivers/input/keyboard/locomokbd.c:270: input_dev->keycodemax = ARRAY_SIZE(locomokbd_keycode);
drivers/input/keyboard/locomokbd.c-271-
--
drivers/input/keyboard/locomokbd.c-273-
drivers/input/keyboard/locomokbd.c:274: memcpy(locomokbd->keycode, locomokbd_keycode, sizeof(locomokbd->keycode));
drivers/input/keyboard/locomokbd.c-275- for (i = 0; i < LOCOMOKBD_NUMKEYS; i++)
--
drivers/input/keyboard/maple_keyb.c=26=struct dc_kbd {
--
drivers/input/keyboard/maple_keyb.c-32-
drivers/input/keyboard/maple_keyb.c:33:static const unsigned short dc_kbd_keycode[NR_SCANCODES] = {
drivers/input/keyboard/maple_keyb.c-34- KEY_RESERVED, KEY_RESERVED, KEY_RESERVED, KEY_RESERVED, KEY_A, KEY_B,
--
drivers/input/keyboard/maple_keyb.c=143=static int probe_maple_kbd(struct device *dev)
--
drivers/input/keyboard/maple_keyb.c-166- kbd->dev = idev;
drivers/input/keyboard/maple_keyb.c:167: memcpy(kbd->keycode, dc_kbd_keycode, sizeof(kbd->keycode));
drivers/input/keyboard/maple_keyb.c-168-
--
drivers/input/keyboard/maple_keyb.c-177- for (i = 0; i < NR_SCANCODES; i++)
drivers/input/keyboard/maple_keyb.c:178: __set_bit(dc_kbd_keycode[i], idev->keybit);
drivers/input/keyboard/maple_keyb.c-179- __clear_bit(KEY_RESERVED, idev->keybit);
--
drivers/input/keyboard/newtonkbd.c=19=MODULE_LICENSE("GPL");
--
drivers/input/keyboard/newtonkbd.c-23-
drivers/input/keyboard/newtonkbd.c:24:static unsigned char nkbd_keycode[128] = {
drivers/input/keyboard/newtonkbd.c-25- KEY_A, KEY_S, KEY_D, KEY_F, KEY_H, KEY_G, KEY_Z, KEY_X,
--
drivers/input/keyboard/newtonkbd.c=64=static int nkbd_connect(struct serio *serio, struct serio_driver *drv)
--
drivers/input/keyboard/newtonkbd.c-78- snprintf(nkbd->phys, sizeof(nkbd->phys), "%s/input0", serio->phys);
drivers/input/keyboard/newtonkbd.c:79: memcpy(nkbd->keycode, nkbd_keycode, sizeof(nkbd->keycode));
drivers/input/keyboard/newtonkbd.c-80-
--
drivers/input/keyboard/newtonkbd.c-91- input_dev->keycodesize = sizeof(unsigned char);
drivers/input/keyboard/newtonkbd.c:92: input_dev->keycodemax = ARRAY_SIZE(nkbd_keycode);
drivers/input/keyboard/newtonkbd.c-93- for (i = 0; i < 128; i++)
--
drivers/input/keyboard/stowaway.c=22=MODULE_LICENSE("GPL");
--
drivers/input/keyboard/stowaway.c-26-
drivers/input/keyboard/stowaway.c:27:static unsigned char skbd_keycode[128] = {
drivers/input/keyboard/stowaway.c-28- KEY_1, KEY_2, KEY_3, KEY_Z, KEY_4, KEY_5, KEY_6, KEY_7,
--
drivers/input/keyboard/stowaway.c=68=static int skbd_connect(struct serio *serio, struct serio_driver *drv)
--
drivers/input/keyboard/stowaway.c-82- snprintf(skbd->phys, sizeof(skbd->phys), "%s/input0", serio->phys);
drivers/input/keyboard/stowaway.c:83: memcpy(skbd->keycode, skbd_keycode, sizeof(skbd->keycode));
drivers/input/keyboard/stowaway.c-84-
--
drivers/input/keyboard/stowaway.c-95- input_dev->keycodesize = sizeof(unsigned char);
drivers/input/keyboard/stowaway.c:96: input_dev->keycodemax = ARRAY_SIZE(skbd_keycode);
drivers/input/keyboard/stowaway.c:97: for (i = 0; i < ARRAY_SIZE(skbd_keycode); i++)
drivers/input/keyboard/stowaway.c:98: set_bit(skbd_keycode[i], input_dev->keybit);
drivers/input/keyboard/stowaway.c-99- clear_bit(0, input_dev->keybit);
--
drivers/input/keyboard/sunkbd.c=23=MODULE_LICENSE("GPL");
drivers/input/keyboard/sunkbd.c-24-
drivers/input/keyboard/sunkbd.c:25:static unsigned char sunkbd_keycode[128] = {
drivers/input/keyboard/sunkbd.c-26- 0,128,114,129,115, 59, 60, 68, 61, 87, 62, 88, 63,100, 64,112,
--
drivers/input/keyboard/sunkbd.c=56=struct sunkbd {
drivers/input/keyboard/sunkbd.c:57: unsigned char keycode[ARRAY_SIZE(sunkbd_keycode)];
drivers/input/keyboard/sunkbd.c-58- struct input_dev *dev;
--
drivers/input/keyboard/sunkbd.c=258=static int sunkbd_connect(struct serio *serio, struct serio_driver *drv)
--
drivers/input/keyboard/sunkbd.c-288- "Sun Type %d keyboard", sunkbd->type);
drivers/input/keyboard/sunkbd.c:289: memcpy(sunkbd->keycode, sunkbd_keycode, sizeof(sunkbd->keycode));
drivers/input/keyboard/sunkbd.c-290-
--
drivers/input/keyboard/sunkbd.c-310- input_dev->keycodesize = sizeof(unsigned char);
drivers/input/keyboard/sunkbd.c:311: input_dev->keycodemax = ARRAY_SIZE(sunkbd_keycode);
drivers/input/keyboard/sunkbd.c:312: for (i = 0; i < ARRAY_SIZE(sunkbd_keycode); i++)
drivers/input/keyboard/sunkbd.c-313- __set_bit(sunkbd->keycode[i], input_dev->keybit);
--
drivers/input/keyboard/xtkbd.c=19=MODULE_LICENSE("GPL");
--
drivers/input/keyboard/xtkbd.c-25-
drivers/input/keyboard/xtkbd.c:26:static unsigned char xtkbd_keycode[256] = {
drivers/input/keyboard/xtkbd.c-27- 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15,
--
drivers/input/keyboard/xtkbd.c=66=static int xtkbd_connect(struct serio *serio, struct serio_driver *drv)
--
drivers/input/keyboard/xtkbd.c-80- snprintf(xtkbd->phys, sizeof(xtkbd->phys), "%s/input0", serio->phys);
drivers/input/keyboard/xtkbd.c:81: memcpy(xtkbd->keycode, xtkbd_keycode, sizeof(xtkbd->keycode));
drivers/input/keyboard/xtkbd.c-82-
--
drivers/input/keyboard/xtkbd.c-93- input_dev->keycodesize = sizeof(unsigned char);
drivers/input/keyboard/xtkbd.c:94: input_dev->keycodemax = ARRAY_SIZE(xtkbd_keycode);
drivers/input/keyboard/xtkbd.c-95-
--
drivers/media/rc/ir-mce_kbd-decoder.c=46=enum mce_kbd_state {
--
drivers/media/rc/ir-mce_kbd-decoder.c-54-
drivers/media/rc/ir-mce_kbd-decoder.c:55:static unsigned char kbd_keycodes[256] = {
drivers/media/rc/ir-mce_kbd-decoder.c-56- KEY_RESERVED, KEY_RESERVED, KEY_RESERVED, KEY_RESERVED, KEY_A,
--
drivers/media/rc/ir-mce_kbd-decoder.c=110=static void mce_kbd_rx_timeout(struct timer_list *t)
--
drivers/media/rc/ir-mce_kbd-decoder.c-123- for (i = 0; i < 7; i++) {
drivers/media/rc/ir-mce_kbd-decoder.c:124: maskcode = kbd_keycodes[MCIR2_MASK_KEYS_START + i];
drivers/media/rc/ir-mce_kbd-decoder.c-125- input_report_key(raw->dev->input_dev, maskcode, 0);
--
drivers/media/rc/ir-mce_kbd-decoder.c-128- for (i = 0; i < MCIR2_MASK_KEYS_START; i++)
drivers/media/rc/ir-mce_kbd-decoder.c:129: input_report_key(raw->dev->input_dev, kbd_keycodes[i],
drivers/media/rc/ir-mce_kbd-decoder.c-130- 0);
--
drivers/media/rc/ir-mce_kbd-decoder.c=149=static void ir_mce_kbd_process_keyboard_data(struct rc_dev *dev, u32 scancode)
--
drivers/media/rc/ir-mce_kbd-decoder.c-160- for (i = 0; i < 7; i++) {
drivers/media/rc/ir-mce_kbd-decoder.c:161: maskcode = kbd_keycodes[MCIR2_MASK_KEYS_START + i];
drivers/media/rc/ir-mce_kbd-decoder.c-162- if (shiftmask & (1 << i))
--
drivers/media/rc/ir-mce_kbd-decoder.c-169- if (keydata1)
drivers/media/rc/ir-mce_kbd-decoder.c:170: input_report_key(dev->input_dev, kbd_keycodes[keydata1], 1);
drivers/media/rc/ir-mce_kbd-decoder.c-171- if (keydata2)
drivers/media/rc/ir-mce_kbd-decoder.c:172: input_report_key(dev->input_dev, kbd_keycodes[keydata2], 1);
drivers/media/rc/ir-mce_kbd-decoder.c-173-
--
drivers/media/rc/ir-mce_kbd-decoder.c-175- for (i = 0; i < MCIR2_MASK_KEYS_START; i++)
drivers/media/rc/ir-mce_kbd-decoder.c:176: input_report_key(dev->input_dev, kbd_keycodes[i], 0);
drivers/media/rc/ir-mce_kbd-decoder.c-177- }
--
drivers/s390/char/con3270.c=671=static void tty3270_read_tasklet(unsigned long data)
--
drivers/s390/char/con3270.c-720- while (len-- > 0)
drivers/s390/char/con3270.c:721: kbd_keycode(tp->kbd, *input++);
drivers/s390/char/con3270.c-722- /* Emit keycode for AID byte. */
drivers/s390/char/con3270.c:723: kbd_keycode(tp->kbd, 256 + tp->input[0]);
drivers/s390/char/con3270.c-724-
--
drivers/s390/char/keyboard.c=307=void
drivers/s390/char/keyboard.c:308:kbd_keycode(struct kbd_data *kbd, unsigned int keycode)
drivers/s390/char/keyboard.c-309-{
--
drivers/s390/char/keyboard.c=579=EXPORT_SYMBOL(kbd_alloc);
drivers/s390/char/keyboard.c:580:EXPORT_SYMBOL(kbd_keycode);
--
drivers/s390/char/keyboard.h=47=void kbd_ascebc(struct kbd_data *, unsigned char *);
drivers/s390/char/keyboard.h-48-
drivers/s390/char/keyboard.h:49:void kbd_keycode(struct kbd_data *, unsigned int);
drivers/s390/char/keyboard.h-50-int kbd_ioctl(struct kbd_data *, unsigned int, unsigned long);
--
drivers/tty/vt/keyboard.c=1414=static void kbd_rawcode(unsigned char data)
--
drivers/tty/vt/keyboard.c-1422-
drivers/tty/vt/keyboard.c:1423:static void kbd_keycode(unsigned int keycode, int down, bool hw_raw)
drivers/tty/vt/keyboard.c-1424-{
--
drivers/tty/vt/keyboard.c=1574=static void kbd_event(struct input_handle *handle, unsigned int event_type,
--
drivers/tty/vt/keyboard.c-1582- if (event_type == EV_KEY && event_code <= KEY_MAX)
drivers/tty/vt/keyboard.c:1583: kbd_keycode(event_code, value, kbd_is_hw_raw(handle->dev));
drivers/tty/vt/keyboard.c-1584- }
]
|
| 12/2 |
2026/05/18 03:07 |
llm |
expert |
0m
Model:
Tokens:
input: 20524
output: 41
thoughts: 211
Thoughts: Here's my analysis of the situation:
**Keyboard Event Handling Deep Dive**
Okay, so the kernel's handling a keyboard event. I see a `kbd_keycode` function call, which in turn triggers an `atomic_notifier_call_chain` on `keyboard_notifier_list` with a `KBD_KEYCODE` event. Standard notifier chain setup, nothing unexpected there.
Hold on, the stack trace... interesting. It's pointing me directly into `rt_mutex_slowunlock`, and then through `kbd_keycode` (inline, of course), ultimately ending in `kbd_event` within the virtual terminal keyboard driver. Let's pinpoint where we are in `drivers/tty/vt/keyboard.c`. Line 1565 looks promising. And there it is: `(*k_handler[type])(vc, KVAL(keysym), !down);`.
Right, `k_handler`. That's the key. It's an array of function pointers. It's starting to make sense. This is how the kernel dispatches specific keypresses or releases based on the 'type' of the event. I need to investigate what `k_handler` contains. It's likely an array of handlers for different key types, mapping the input to specific actions. I will next look at the `k_handler` array.
|
| 13/2 |
2026/05/18 03:07 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/tty/vt/keyboard.c IncludeLines:true Name:k_handler]
Results: map[SourceCode: 82: static k_handler_fn *k_handler[16] = { K_HANDLERS };
SourceFile:drivers/tty/vt/keyboard.c]
|
| 14/2 |
2026/05/18 03:07 |
llm |
expert |
0m
Model:
Tokens:
input: 21126
output: 19
thoughts: 14
Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience and written in the first person:
**Decoding `K_HANDLERS`**
Okay, let's dive into this. The code is referencing `K_HANDLERS`. My initial thought is to figure out what precisely this variable, object, or macro represents. Given the naming convention, it's likely a container for "handler" functions, possibly related to kernel-level operations or interrupt handling, but I want to confirm that. Is this a table of function pointers? A dictionary? A custom data structure? Understanding the structure of `K_HANDLERS` is going to be key to interpreting the subsequent logic, as it's the gateway to understanding what specific handlers are present and how they are utilized within the system's execution flow. I need to quickly identify the definition of this structure to understand it better, and get a better picture of the design approach being used here.
|
| 15/2 |
2026/05/18 03:07 |
tool |
grepper |
0m
Args: map[Expression:K_HANDLERS]
Results: map[Output:drivers/s390/char/keyboard.c-25- */
drivers/s390/char/keyboard.c:26:#define K_HANDLERS\
drivers/s390/char/keyboard.c-27- k_self, k_fn, k_spec, k_ignore,\
--
drivers/s390/char/keyboard.c=32=typedef void (k_handler_fn)(struct kbd_data *, unsigned char);
drivers/s390/char/keyboard.c:33:static k_handler_fn K_HANDLERS;
drivers/s390/char/keyboard.c:34:static k_handler_fn *k_handler[16] = { K_HANDLERS };
drivers/s390/char/keyboard.c-35-
--
drivers/tty/vt/keyboard.c=61=static inline int kbd_defleds(void)
--
drivers/tty/vt/keyboard.c-72-
drivers/tty/vt/keyboard.c:73:#define K_HANDLERS\
drivers/tty/vt/keyboard.c-74- k_self, k_fn, k_spec, k_pad,\
--
drivers/tty/vt/keyboard.c=79=typedef void (k_handler_fn)(struct vc_data *vc, unsigned char value,
drivers/tty/vt/keyboard.c-80- char up_flag);
drivers/tty/vt/keyboard.c:81:static k_handler_fn K_HANDLERS;
drivers/tty/vt/keyboard.c:82:static k_handler_fn *k_handler[16] = { K_HANDLERS };
drivers/tty/vt/keyboard.c-83-
]
|
| 16/2 |
2026/05/18 03:07 |
llm |
expert |
0m
Model:
Tokens:
input: 21805
output: 41
thoughts: 706
Thoughts: **Debugging a Potential Use-After-Free in the Keyboard Handler**
Okay, let's dive into this. I'm looking at `K_HANDLERS` in `drivers/tty/vt/keyboard.c`, just to get a lay of the land. Now, I see a few key handler functions defined. The initial stack trace is suggesting something related to `rt_mutex_slowunlock` or something similar, and the trace points to `_raw_spin_lock_irqsave`. I'm going through the call stack: `kbd_keycode` calls `kbd_event` which leads to a lock acquire call.
Something's not quite right. `rt_mutex_slowunlock` shouldn't be called directly by `kbd_keycode`. Hmm, let's retrace that: I'm seeing `rt_mutex_slowunlock` in `kernel/locking/rtmutex.c`. It's not the direct path. Wait a minute... is `rt_mutex_slowunlock` perhaps called indirectly by something in a PREEMPT_RT kernel? Ah, the kernel *is* PREEMPT_RT, as indicated by the taint flag. Bingo!
In PREEMPT_RT, `spin_unlock_irqrestore` maps to `rt_spin_unlock_irqrestore`, which *could* call `rt_mutex_slowunlock`. That's the link I was looking for. Now, if that's the case, then a use-after-free situation is likely lurking within `spin_unlock_irqrestore(&lock)` or perhaps even plain `spin_unlock(&lock)`. Time to start looking at where these spin locks are being used in `kbd_keycode`. I need to zero in on that section of the code.
Okay, let's go back to the source code. The call stack points to `kbd_keycode` around line 1565. Ah, line 1565 is `(*k_handler[type])(vc, KVAL(keysym), !down);` But wait, `kbd_keycode` could be inlined, so the line number might be misleading. I need to keep the context of `kbd_keycode` in mind. Let's trace it through again.
|
| 17/2 |
2026/05/18 03:07 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/tty/vt/keyboard.c IncludeLines:true Name:kbd_keycode]
Results: map[SourceCode:1423: static void kbd_keycode(unsigned int keycode, int down, bool hw_raw)
1424: {
1425: struct vc_data *vc = vc_cons[fg_console].d;
1426: unsigned short keysym, *key_map;
1427: unsigned char type;
1428: bool raw_mode;
1429: struct tty_struct *tty;
1430: int shift_final;
1431: struct keyboard_notifier_param param = { .vc = vc, .value = keycode, .down = down };
1432: int rc;
1433:
1434: tty = vc->port.tty;
1435:
1436: if (tty && (!tty->driver_data)) {
1437: /* No driver data? Strange. Okay we fix it then. */
1438: tty->driver_data = vc;
1439: }
1440:
1441: kbd = &kbd_table[vc->vc_num];
1442:
1443: #ifdef CONFIG_SPARC
1444: if (keycode == KEY_STOP)
1445: sparc_l1_a_state = down;
1446: #endif
1447:
1448: rep = (down == 2);
1449:
1450: raw_mode = (kbd->kbdmode == VC_RAW);
1451: if (raw_mode && !hw_raw)
1452: if (emulate_raw(vc, keycode, !down << 7))
1453: if (keycode < BTN_MISC && printk_ratelimit())
1454: pr_warn("can't emulate rawmode for keycode %d\n",
1455: keycode);
1456:
1457: #ifdef CONFIG_SPARC
1458: if (keycode == KEY_A && sparc_l1_a_state) {
1459: sparc_l1_a_state = false;
1460: sun_do_break();
1461: }
1462: #endif
1463:
1464: if (kbd->kbdmode == VC_MEDIUMRAW) {
1465: /*
1466: * This is extended medium raw mode, with keys above 127
1467: * encoded as 0, high 7 bits, low 7 bits, with the 0 bearing
1468: * the 'up' flag if needed. 0 is reserved, so this shouldn't
1469: * interfere with anything else. The two bytes after 0 will
1470: * always have the up flag set not to interfere with older
1471: * applications. This allows for 16384 different keycodes,
1472: * which should be enough.
1473: */
1474: if (keycode < 128) {
1475: put_queue(vc, keycode | (!down << 7));
1476: } else {
1477: put_queue(vc, !down << 7);
1478: put_queue(vc, (keycode >> 7) | BIT(7));
1479: put_queue(vc, keycode | BIT(7));
1480: }
1481: raw_mode = true;
1482: }
1483:
1484: assign_bit(keycode, key_down, down);
1485:
1486: if (rep &&
1487: (!vc_kbd_mode(kbd, VC_REPEAT) ||
1488: (tty && !L_ECHO(tty) && tty_chars_in_buffer(tty)))) {
1489: /*
1490: * Don't repeat a key if the input buffers are not empty and the
1491: * characters get aren't echoed locally. This makes key repeat
1492: * usable with slow applications and under heavy loads.
1493: */
1494: return;
1495: }
1496:
1497: param.shift = shift_final = (shift_state | kbd->slockstate) ^ kbd->lockstate;
1498: param.ledstate = kbd->ledflagstate;
1499: key_map = key_maps[shift_final];
1500:
1501: /*
1502: * Fall back to the plain map if modifiers are active, the modifier-
1503: * specific map is missing or has no entry, and the plain map has a
1504: * modifier-aware key type (KT_CUR or KT_CSI). These handlers encode
1505: * the modifier state into the emitted escape sequence.
1506: */
1507: if (shift_final && keycode < NR_KEYS &&
1508: (!key_map || key_map[keycode] == K_HOLE) && key_maps[0]) {
1509: unsigned short plain = key_maps[0][keycode];
1510: unsigned char type = KTYP(plain);
1511:
1512: if (type >= 0xf0 && (type - 0xf0 == KT_CUR || type - 0xf0 == KT_CSI))
1513: key_map = key_maps[0];
1514: }
1515:
1516: rc = atomic_notifier_call_chain(&keyboard_notifier_list,
1517: KBD_KEYCODE, ¶m);
1518: if (rc == NOTIFY_STOP || !key_map) {
1519: atomic_notifier_call_chain(&keyboard_notifier_list,
1520: KBD_UNBOUND_KEYCODE, ¶m);
1521: do_compute_shiftstate();
1522: kbd->slockstate = 0;
1523: return;
1524: }
1525:
1526: if (keycode < NR_KEYS)
1527: keysym = key_map[keycode];
1528: else if (keycode >= KEY_BRL_DOT1 && keycode <= KEY_BRL_DOT8)
1529: keysym = U(K(KT_BRL, keycode - KEY_BRL_DOT1 + 1));
1530: else
1531: return;
1532:
1533: type = KTYP(keysym);
1534:
1535: if (type < 0xf0) {
1536: param.value = keysym;
1537: rc = atomic_notifier_call_chain(&keyboard_notifier_list,
1538: KBD_UNICODE, ¶m);
1539: if (rc != NOTIFY_STOP)
1540: if (down && !(raw_mode || kbd->kbdmode == VC_OFF))
1541: k_unicode(vc, keysym, !down);
1542: return;
1543: }
1544:
1545: type -= 0xf0;
1546:
1547: if (type == KT_LETTER) {
1548: type = KT_LATIN;
1549: if (vc_kbd_led(kbd, VC_CAPSLOCK)) {
1550: key_map = key_maps[shift_final ^ BIT(KG_SHIFT)];
1551: if (key_map)
1552: keysym = key_map[keycode];
1553: }
1554: }
1555:
1556: param.value = keysym;
1557: rc = atomic_notifier_call_chain(&keyboard_notifier_list,
1558: KBD_KEYSYM, ¶m);
1559: if (rc == NOTIFY_STOP)
1560: return;
1561:
1562: if ((raw_mode || kbd->kbdmode == VC_OFF) && type != KT_SPEC && type != KT_SHIFT)
1563: return;
1564:
1565: (*k_handler[type])(vc, KVAL(keysym), !down);
1566:
1567: param.ledstate = kbd->ledflagstate;
1568: atomic_notifier_call_chain(&keyboard_notifier_list, KBD_POST_KEYSYM, ¶m);
1569:
1570: if (type != KT_SLOCK)
1571: kbd->slockstate = 0;
1572: }
SourceFile:drivers/tty/vt/keyboard.c]
|
| 18/2 |
2026/05/18 03:07 |
llm |
expert |
0m
Model:
Tokens:
input: 25416
output: 45
thoughts: 132
Thoughts: **UAF Potential in `tty_chars_in_buffer`!**
Okay, hold on a second. Line 1488, right there... `tty_chars_in_buffer(tty)` is being called. My spidey-sense is tingling. Looking at the surrounding code, there's a potential for a Use-After-Free condition. If the `tty` pointer gets freed *before* this check is evaluated, we're going to have a bad day with a UAF! It looks like there's a conditional check before the call. It looks like it could happen if `rep` is true, the keyboard isn't in repeat mode, the tty exists, and echo is disabled on the line. I need to dive into how `tty_chars_in_buffer` handles its `tty` argument and verify that there is no possibility of this happening.
|
| 19/2 |
2026/05/18 03:07 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/tty/tty_ioctl.c IncludeLines:true Name:tty_chars_in_buffer]
Results: map[SourceCode: 41: /**
42: * tty_chars_in_buffer - characters pending
43: * @tty: terminal
44: *
45: * Returns: the number of bytes of data in the device private output queue. If
46: * no private method is supplied there is assumed to be no queue on the device.
47: */
48: unsigned int tty_chars_in_buffer(struct tty_struct *tty)
49: {
50: if (tty->ops->chars_in_buffer)
51: return tty->ops->chars_in_buffer(tty);
52: return 0;
53: }
SourceFile:drivers/tty/tty_ioctl.c]
|
| 20/2 |
2026/05/18 03:07 |
llm |
expert |
0m
Model:
Tokens:
input: 25996
output: 41
thoughts: 589
Thoughts: **Debugging a Lock Contention Issue**
Okay, so `tty_chars_in_buffer` shouldn't be taking any locks. But the stack trace is screaming otherwise. Let's see... the trace shows `lock_acquire`, then `__raw_spin_lock_irqsave`, all the way down to `rt_mutex_slowunlock` which is pretty suspicious. And it points to `kbd_event` in `drivers/tty/vt/keyboard.c`, specifically around the `k_handler` function calls, specifically `(*k_handler[type])(vc, KVAL(keysym), !down);` at line 1565.
I need to figure out which of those handlers could be the culprit. Is it `k_fn`, `k_spec`, `k_self`, or `k_shift` that's causing this? Or, under PREEMPT_RT, maybe the `spin_unlock_irqrestore` translation to `rt_spin_unlock_irqrestore` is the cause? No, `rt_spin_unlock` *itself* doesn't call `rt_mutex_slowunlock`. It calls `__rt_spin_unlock` which calls `rt_mutex_slowunlock`. That's not the path the stack trace takes. It seems to go from `kbd_keycode` directly to `rt_mutex_slowunlock`. But wait, that makes no sense.
`kbd_keycode` is an inline function. Maybe `spin_unlock_irqrestore` is being inlined? Let me check `k_unicode`, `put_queue`, or something related. Okay, nope, `kbd_keycode` itself doesn't have any `spin_unlock_irqrestore` calls.
Okay, let me look at `kbd_keycode` again. Wait a second... it's `kbd_event` that actually *does* have a `spin_lock_irqsave(&kbd_event_lock, flags);` and `spin_unlock_irqrestore(&kbd_event_lock, flags);`! That's the likely source. Time to focus on `kbd_event` and figure out what it's locking.
|
| 21/2 |
2026/05/18 03:07 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/tty/vt/keyboard.c IncludeLines:true Name:kbd_event]
Results: map[SourceCode:1574: static void kbd_event(struct input_handle *handle, unsigned int event_type,
1575: unsigned int event_code, int value)
1576: {
1577: /* We are called with interrupts disabled, just take the lock */
1578: scoped_guard(spinlock, &kbd_event_lock) {
1579: if (event_type == EV_MSC && event_code == MSC_RAW &&
1580: kbd_is_hw_raw(handle->dev))
1581: kbd_rawcode(value);
1582: if (event_type == EV_KEY && event_code <= KEY_MAX)
1583: kbd_keycode(event_code, value, kbd_is_hw_raw(handle->dev));
1584: }
1585:
1586: tasklet_schedule(&keyboard_tasklet);
1587: do_poke_blanked_console = 1;
1588: schedule_console_callback();
1589: }
SourceFile:drivers/tty/vt/keyboard.c]
|
| 22/2 |
2026/05/18 03:07 |
llm |
expert |
0m
Model:
Tokens:
input: 27409
output: 43
thoughts: 446
Thoughts: **Debugging a Kernel Lock Issue**
Okay, so I'm looking at this stack trace and immediately, I spot the `scoped_guard(spinlock, &kbd_event_lock)`. My mind immediately goes to, "Right, `scoped_guard` expands to lock and unlock the spinlock." The unlock, I'm pretty sure, happens at the end of the `scoped_guard`'s scope, which in this case is line 1584. But the stack trace is pointing the finger at `rt_mutex_slowunlock` and showing a call from `kbd_event` at line 1583.
Wait a second, line 1583 is `kbd_keycode`. If that function is inlined by the compiler, the unlock might get attributed to the last line of the block, which would be in the inlined `kbd_keycode` code. So, maybe the problem is actually buried within `kbd_keycode` itself, perhaps at that line 1565.
But then I think, why is `rt_mutex_slowunlock` even messing with a freed `tty_struct`? The unlock function is supposed to access the *lock* itself, which is the global `kbd_event_lock`. That's a global variable, and that should be fine.
Aha! The address that's buggy is `ffff888051204418`. Looking at that address, it looks like it belongs to `kmalloc-cg-2k` of size 2048. And I recall, from the memory allocator metadata, that it was allocated by `alloc_tty_struct`. So, that address is *inside* a `tty_struct`. That raises more questions. Why on earth would `rt_mutex_slowunlock` be trying to access something within a `tty_struct`? Something must have gone very, very wrong. I'll need to go look at `rt_mutex_slowunlock` code itself in `kernel/locking/rtmutex.c:1426`.
|
| 23/2 |
2026/05/18 03:07 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/locking/rtmutex.c IncludeLines:true Name:rt_mutex_slowunlock]
Results: map[SourceCode:1417: /*
1418: * Slow path to release a rt-mutex.
1419: */
1420: static void __sched rt_mutex_slowunlock(struct rt_mutex_base *lock)
1421: {
1422: DEFINE_RT_WAKE_Q(wqh);
1423: unsigned long flags;
1424:
1425: /* irqsave required to support early boot calls */
1426: raw_spin_lock_irqsave(&lock->wait_lock, flags);
1427:
1428: debug_rt_mutex_unlock(lock);
1429:
1430: /*
1431: * We must be careful here if the fast path is enabled. If we
1432: * have no waiters queued we cannot set owner to NULL here
1433: * because of:
1434: *
1435: * foo->lock->owner = NULL;
1436: * rtmutex_lock(foo->lock); <- fast path
1437: * free = atomic_dec_and_test(foo->refcnt);
1438: * rtmutex_unlock(foo->lock); <- fast path
1439: * if (free)
1440: * kfree(foo);
1441: * raw_spin_unlock(foo->lock->wait_lock);
1442: *
1443: * So for the fastpath enabled kernel:
1444: *
1445: * Nothing can set the waiters bit as long as we hold
1446: * lock->wait_lock. So we do the following sequence:
1447: *
1448: * owner = rt_mutex_owner(lock);
1449: * clear_rt_mutex_waiters(lock);
1450: * raw_spin_unlock(&lock->wait_lock);
1451: * if (cmpxchg(&lock->owner, owner, 0) == owner)
1452: * return;
1453: * goto retry;
1454: *
1455: * The fastpath disabled variant is simple as all access to
1456: * lock->owner is serialized by lock->wait_lock:
1457: *
1458: * lock->owner = NULL;
1459: * raw_spin_unlock(&lock->wait_lock);
1460: */
1461: while (!rt_mutex_has_waiters(lock)) {
1462: /* Drops lock->wait_lock ! */
1463: if (unlock_rt_mutex_safe(lock, flags) == true)
1464: return;
1465: /* Relock the rtmutex and try again */
1466: raw_spin_lock_irqsave(&lock->wait_lock, flags);
1467: }
1468:
1469: /*
1470: * The wakeup next waiter path does not suffer from the above
1471: * race. See the comments there.
1472: *
1473: * Queue the next waiter for wakeup once we release the wait_lock.
1474: */
1475: mark_wakeup_next_waiter(&wqh, lock);
1476: raw_spin_unlock_irqrestore(&lock->wait_lock, flags);
1477:
1478: rt_mutex_wake_up_q(&wqh);
1479: }
SourceFile:kernel/locking/rtmutex.c]
|
| 24/2 |
2026/05/18 03:08 |
llm |
expert |
0m
Model:
Tokens:
input: 29329
output: 41
thoughts: 468
Thoughts: **Debugging a Potential Use-After-Free in the Kernel**
Okay, so I'm looking at this call to `rt_mutex_slowunlock`, and the argument `lock` is what's catching my eye. If `lock` is a member of a `tty_struct`, and that `tty_struct` has been freed, then that `raw_spin_lock_irqsave` call within `rt_mutex_slowunlock` will try to access freed memory, which is obviously bad news. But hold on a second... `kbd_event_lock` *is* a global spinlock, so why would the `lock` passed to this function even be related to a `tty_struct`? Something's not adding up.
Alright, let's step back and re-examine the stack trace. The trace clearly shows `rt_mutex_slowunlock` being called, which then calls `_raw_spin_lock_irqsave`, and that call is coming from `kbd_event`. My spider sense is tingling β is there some kind of spinlock lurking inside a `tty_struct` that's being unlocked in `kbd_keycode`? That's the only plausible explanation, I think.
Let's dive into line 1565 of `drivers/tty/vt/keyboard.c`. It looks like `kbd_event` is calling a function pointer through `k_handler`. So this would have to be handled by one of these handlers. I see the lock being passed by calling `(*k_handler[type])(vc, KVAL(keysym), !down);` Maybe one of these function calls unlocks the spinlock inside the tty_struct. Let's see... looking at the code, it seems the handler array `k_handler` contains `k_unicode`, `k_fn`, `k_spec`, `k_shift`, and `k_ascii` handlers. I'm going to quickly check those, starting with `fn_handler` and `k_fn`.
|
| 25/2 |
2026/05/18 03:08 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/tty/vt/keyboard.c IncludeLines:true Name:k_fn]
Results: map[SourceCode: 752: static void k_fn(struct vc_data *vc, unsigned char value, char up_flag)
753: {
754: if (up_flag)
755: return;
756:
757: if ((unsigned)value < ARRAY_SIZE(func_table)) {
758: guard(spinlock_irqsave)(&func_buf_lock);
759: if (func_table[value])
760: puts_queue(vc, func_table[value]);
761: } else
762: pr_err("k_fn called with value=%d\n", value);
763: }
SourceFile:drivers/tty/vt/keyboard.c]
|
| 26/2 |
2026/05/18 03:08 |
llm |
expert |
0m
Model:
Tokens:
input: 30487
output: 41
thoughts: 9
Thoughts: Okay, here's my interpretation of that thought process, tailored for an expert audience, and written in the first person:
**Analyzing the `puts_queue`**
Right, let's take a look at `puts_queue`. My immediate thought is, what's its state? What's the context? Is this related to debugging a threading issue, a performance bottleneck, or simply a matter of resource management? I'm assuming that "puts" refers to some sort of output queue, likely in a concurrent or asynchronous environment. My mind immediately starts running through possible scenarios: Is it a simple buffer for `puts` calls in a specific thread? Is it a more complex queue implemented for inter-process communication?
I need to understand what's *in* this queue. Are we dealing with raw strings, formatted data structures, or serialized objects? The data type drastically affects my approach. Are there any contention issues? Are locks involved? Is the queue implemented with bounded capacity? Overflow handling is always a critical concern here. The current implementation details will be key to understanding the potential failure points and, how to improve the performance.
Essentially, I need to understand what's happening with the output, the source and destination of the data being output, and how it is being done to determine if there are performance issues, or to determine whether there is an issue to be addressed in the first place.
|
| 27/2 |
2026/05/18 03:08 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/tty/vt/keyboard.c IncludeLines:true Name:puts_queue]
Results: map[SourceCode: 332: static void puts_queue(struct vc_data *vc, const char *cp)
333: {
334: tty_insert_flip_string(&vc->port, cp, strlen(cp));
335: tty_flip_buffer_push(&vc->port);
336: }
SourceFile:drivers/tty/vt/keyboard.c]
|
| 28/2 |
2026/05/18 03:08 |
llm |
expert |
0m
Model:
Tokens:
input: 30944
output: 45
thoughts: 36
Thoughts: Okay, let's see. My mind immediately jumped to those two functions: `tty_insert_flip_string` and `tty_flip_buffer_push`. Something in the context has triggered them, and now I'm thinking... yep, it's that second one that's the key. I need to refresh my understanding of how `tty_flip_buffer_push` is used and how it interacts with the flip buffer. Time to dive into the code and see exactly what's going on with that function.
|
| 29/2 |
2026/05/18 03:08 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/tty/tty_buffer.c IncludeLines:true Name:tty_flip_buffer_push]
Results: map[SourceCode: 525: /**
526: * tty_flip_buffer_push - push terminal buffers
527: * @port: tty port to push
528: *
529: * Queue a push of the terminal flip buffers to the line discipline. Can be
530: * called from IRQ/atomic context.
531: *
532: * In the event of the queue being busy for flipping the work will be held off
533: * and retried later.
534: */
535: void tty_flip_buffer_push(struct tty_port *port)
536: {
537: struct tty_bufhead *buf = &port->buf;
538:
539: tty_flip_buffer_commit(buf->tail);
540: tty_buffer_queue_work(buf);
541: }
SourceFile:drivers/tty/tty_buffer.c]
|
| 30/2 |
2026/05/18 03:08 |
llm |
expert |
0m
Model:
Tokens:
input: 31419
output: 49
thoughts: 25
Thoughts: Here's my take on those thoughts:
**Analyzing `tty_insert_flip_string`'s Implementation**
Okay, so I'm digging into this `tty_insert_flip_string` function, and it seems like it's a critical piece for how our terminal emulator handles string insertions with potentially flipped characters. The immediate thing that jumps out is the internal call to `tty_insert_flip_string_fixed_flag`. That's the key point; `tty_insert_flip_string` isn't doing the heavy lifting directly. It's delegating a significant part of its functionality to this other, more specific function. I need to understand what this fixed flag refers to, and what that call means to the state of this program. This means I will look into what that fixed flag represents. I have to see how it integrates within the larger picture of character handling and display logic. I need to understand the nuances of the interaction between these two functions before I can be confident in the overall design.
|
| 31/2 |
2026/05/18 03:08 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/tty/tty_buffer.c IncludeLines:true Name:tty_insert_flip_string_fixed_flag]
Results: map[SourceCode: 19: /**
20: * tty_insert_flip_string_fixed_flag - add characters to the tty buffer
21: * @port: tty port
22: * @chars: characters
23: * @flag: flag value for each character
24: * @size: size
25: *
26: * Queue a series of bytes to the tty buffering. All the characters passed are
27: * marked with the supplied flag.
28: *
29: * Returns: the number added.
30: */
31: static inline size_t tty_insert_flip_string_fixed_flag(struct tty_port *port,
32: const u8 *chars, u8 flag,
33: size_t size)
34: {
35: return __tty_insert_flip_string_flags(port, chars, &flag, false, size);
36: }
SourceFile:include/linux/tty_flip.h]
|
| 32/2 |
2026/05/18 03:08 |
llm |
expert |
0m
Model:
Tokens:
input: 31997
output: 48
thoughts: 16
Thoughts: Okay, let's dive into this. Here's my take on those thoughts, as if they're my own:
**Investigating `__tty_insert_flip_string_flags`**
Alright, time to get to it. Let's see what's happening with `__tty_insert_flip_string_flags`. That function name itself is a pretty big hint, isn't it? It sounds like we're inserting a string, likely into a TTY buffer, and there are some "flip" and "flags" involved. This tells me this probably has to do with how the driver handles data, perhaps marking characters with special attributes or handling character flow control or something of that nature. I need to understand what "flip" refers to in this context. Is it about flipping characters to upper or lowercase, controlling data flow between buffers, changing data formats? The flags are going to be key as well. Are we dealing with character attributes, framing errors, overrun situations, or something more device-specific? I know the TTY layer well, so I'm expecting this function is somewhere in the core layer or perhaps in a driver-specific area. The "insert" part has me thinking we may be doing a raw-buffer operation, so let's start with tracing execution through the function.
|
| 33/2 |
2026/05/18 03:08 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/tty/tty_buffer.c IncludeLines:true Name:__tty_insert_flip_string_flags]
Results: map[SourceCode: 307: size_t __tty_insert_flip_string_flags(struct tty_port *port, const u8 *chars,
308: const u8 *flags, bool mutable_flags,
309: size_t size)
310: {
311: bool need_flags = mutable_flags || flags[0] != TTY_NORMAL;
312: size_t copied = 0;
313:
314: do {
315: size_t goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE);
316: size_t space = __tty_buffer_request_room(port, goal, need_flags);
317: struct tty_buffer *tb = port->buf.tail;
318:
319: if (unlikely(space == 0))
320: break;
321:
322: memcpy(char_buf_ptr(tb, tb->used), chars, space);
323:
324: if (mutable_flags) {
325: memcpy(flag_buf_ptr(tb, tb->used), flags, space);
326: flags += space;
327: } else if (tb->flags) {
328: memset(flag_buf_ptr(tb, tb->used), flags[0], space);
329: } else {
330: /* tb->flags should be available once requested */
331: WARN_ON_ONCE(need_flags);
332: }
333:
334: tb->used += space;
335: copied += space;
336: chars += space;
337:
338: /* There is a small chance that we need to split the data over
339: * several buffers. If this is the case we must loop.
340: */
341: } while (unlikely(size > copied));
342:
343: return copied;
344: }
SourceFile:drivers/tty/tty_buffer.c]
|
| 34/2 |
2026/05/18 03:08 |
llm |
expert |
0m
Model:
Tokens:
input: 32939
output: 46
thoughts: 14
Thoughts: Okay, here's my attempt at summarizing that thought process, tailored for an expert audience:
**Diving into TTY Buffer Space**
Right, let's zero in on `__tty_buffer_request_room`. This function is critical for understanding the mechanics of how data is managed within the TTY subsystem. I need to refresh my memory on the exact implementation details, especially the nuances of how it calculates and allocates buffer space. I'm thinking about its interaction with the various locking mechanisms used to protect the buffer's integrity. Are we talking spinlocks, mutexes, or something more nuanced? What's the potential for contention? And, perhaps most importantly, how efficiently does it handle requests of varying sizes? Does its performance scale predictably under heavy load, or are there hidden bottlenecks lurking? I should also quickly review how this function handles both success and failure cases, to ensure that I am able to comprehend the entire process that it encompasses.
|
| 35/2 |
2026/05/18 03:08 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/tty/tty_buffer.c IncludeLines:true Name:__tty_buffer_request_room]
Results: map[SourceCode: 254: /**
255: * __tty_buffer_request_room - grow tty buffer if needed
256: * @port: tty port
257: * @size: size desired
258: * @flags: buffer has to store flags along character data
259: *
260: * Make at least @size bytes of linear space available for the tty buffer.
261: *
262: * Will change over to a new buffer if the current buffer is encoded as
263: * %TTY_NORMAL (so has no flags buffer) and the new buffer requires a flags
264: * buffer.
265: *
266: * Returns: the size we managed to find.
267: */
268: static int __tty_buffer_request_room(struct tty_port *port, size_t size,
269: bool flags)
270: {
271: struct tty_bufhead *buf = &port->buf;
272: struct tty_buffer *n, *b = buf->tail;
273: size_t left = (b->flags ? 1 : 2) * b->size - b->used;
274: bool change = !b->flags && flags;
275:
276: if (!change && left >= size)
277: return size;
278:
279: /* This is the slow path - looking for new buffers to use */
280: n = tty_buffer_alloc(port, size);
281: if (n == NULL)
282: return change ? 0 : left;
283:
284: n->flags = flags;
285: buf->tail = n;
286: /*
287: * Paired w/ acquire in flush_to_ldisc() and lookahead_bufs()
288: * ensures they see all buffer data.
289: */
290: smp_store_release(&b->commit, b->used);
291: /*
292: * Paired w/ acquire in flush_to_ldisc() and lookahead_bufs()
293: * ensures the latest commit value can be read before the head
294: * is advanced to the next buffer.
295: */
296: smp_store_release(&b->next, n);
297:
298: return size;
299: }
SourceFile:drivers/tty/tty_buffer.c]
|
| 36/2 |
2026/05/18 03:08 |
llm |
expert |
0m
Model:
Tokens:
input: 33923
output: 43
thoughts: 20
Thoughts: Here's a summary of my thought process, as requested:
**Deconstructing a TTY Buffer Allocation**
Okay, let me break this down. My initial observation is that `__tty_buffer_request_room` is the function of interest. The name strongly suggests it's related to requesting or reserving space within a TTY buffer. And the real key is the function `tty_buffer_alloc` being called. That's the allocation mechanism. I'm seeing `__tty_buffer_request_room` is handling the *request* and then, in turn, relying on `tty_buffer_alloc` for the actual *allocation* of memory for a TTY buffer. So, it's a two-step process: request and then allocate. This is pretty standard for memory management, actually. I'd need to dig deeper to understand the specifics of each function, and how they interact.
|
| 37/2 |
2026/05/18 03:08 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/tty/tty_buffer.c IncludeLines:true Name:tty_buffer_alloc]
Results: map[SourceCode: 154: /**
155: * tty_buffer_alloc - allocate a tty buffer
156: * @port: tty port
157: * @size: desired size (characters)
158: *
159: * Allocate a new tty buffer to hold the desired number of characters. We
160: * round our buffers off in 256 character chunks to get better allocation
161: * behaviour.
162: *
163: * Returns: %NULL if out of memory or the allocation would exceed the per
164: * device queue.
165: */
166: static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size)
167: {
168: struct llist_node *free;
169: struct tty_buffer *p;
170:
171: /* Round the buffer size out */
172: size = __ALIGN_MASK(size, TTYB_ALIGN_MASK);
173:
174: if (size <= MIN_TTYB_SIZE) {
175: free = llist_del_first(&port->buf.free);
176: if (free) {
177: p = llist_entry(free, struct tty_buffer, free);
178: goto found;
179: }
180: }
181:
182: /* Should possibly check if this fails for the largest buffer we
183: * have queued and recycle that ?
184: */
185: if (atomic_read(&port->buf.mem_used) > port->buf.mem_limit)
186: return NULL;
187: p = kmalloc_flex(*p, data, 2 * size, GFP_ATOMIC | __GFP_NOWARN);
188: if (p == NULL)
189: return NULL;
190:
191: found:
192: tty_buffer_reset(p, size);
193: atomic_add(size, &port->buf.mem_used);
194: return p;
195: }
SourceFile:drivers/tty/tty_buffer.c]
|
| 38/2 |
2026/05/18 03:08 |
llm |
expert |
0m
Model:
Tokens:
input: 34828
output: 43
thoughts: 655
Thoughts: **Debugging a Potential Lock Contention in the TTY Subsystem**
Okay, let's break this down. I see `tty_buffer_alloc` uses `kmalloc_flex` with `GFP_ATOMIC`. No spinlocks are taken there, so that's not where the lock is. My immediate question is: where's the spinlock? The stack trace is:
```
lock_acquire+0x84/0x350 kernel/locking/lockdep.c:5842
__raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:132 [inline]
_raw_spin_lock_irqsave+0x40/0x60 kernel/locking/spinlock.c:166
rt_mutex_slowunlock+0xbf/0x8b0 kernel/locking/rtmutex.c:1426
kbd_keycode drivers/tty/vt/keyboard.c:1565 [inline]
kbd_event+0x2f91/0x42f0 drivers/tty/vt/keyboard.c:1583
```
This is interesting. `rt_mutex_slowunlock` is called from `kbd_keycode`. But wait, that can't be right; isn't `_raw_spin_lock_irqsave` higher in the call stack? Let me re-examine the stack trace. The correct call stack is:
```
lock_acquire
__raw_spin_lock_irqsave
_raw_spin_lock_irqsave
rt_mutex_slowunlock
kbd_keycode
kbd_event
```
Okay, so `_raw_spin_lock_irqsave` is called by `rt_mutex_slowunlock`. Yes! Looking at the source of `rt_mutex_slowunlock`, I see the critical line:
```c
raw_spin_lock_irqsave(&lock->wait_lock, flags);
```
Ah-ha! `rt_mutex_slowunlock` *does* call `raw_spin_lock_irqsave`. Therefore, `rt_mutex_slowunlock` is the function that calls `_raw_spin_lock_irqsave`. And, yes, `rt_mutex_slowunlock` is indeed called from `kbd_keycode` eventually by the code in this trace. Wait a minute... `rt_mutex_slowunlock` is called by `rt_spin_unlock` or `rt_spin_unlock_irqrestore`, which are likely inlined. Now, I need to check how `rt_spin_unlock` or `spin_unlock_irqrestore` are handled in PREEMPT_RT. I'm going to have to dive into that code path.
|
| 39/2 |
2026/05/18 03:08 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/locking/spinlock_rt.c IncludeLines:true Name:rt_spin_unlock]
Results: map[SourceCode: 78: void __sched rt_spin_unlock(spinlock_t *lock) __releases(RCU)
79: {
80: spin_release(&lock->dep_map, _RET_IP_);
81: migrate_enable();
82: rcu_read_unlock();
83:
84: if (unlikely(!rt_mutex_cmpxchg_release(&lock->lock, current, NULL)))
85: rt_mutex_slowunlock(&lock->lock);
86: }
SourceFile:kernel/locking/spinlock_rt.c]
|
| 40/2 |
2026/05/18 03:08 |
llm |
expert |
0m
Model:
Tokens:
input: 36315
output: 45
thoughts: 73
Thoughts: Okay, let's see, I'm tracing this code and I've hit a pretty important connection.
**Aha! rt_spin_unlock Unlocks the Key**
My initial thought is confirmed: `rt_spin_unlock` *definitely* calls `rt_mutex_slowunlock`! That's a crucial link I was hoping to find. Now, I'm quickly assessing the execution path. Is `rt_spin_unlock` inlined, or perhaps optimized as a tail call? It looks like it's not inlined. Maybe it's a tail call? I should double-check the assembly output to be certain. Hang on, is it possible that `spin_unlock_irqrestore` is the function that actually calls `rt_spin_unlock`? Gotta follow that thread and see if it yields further insight into the locking and unlocking mechanics. It's all about understanding the call stack here.
|
| 41/2 |
2026/05/18 03:08 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/locking/spinlock_rt.c IncludeLines:true Name:spin_unlock_irqrestore]
Results: map[SourceCode: 125: static __always_inline void spin_unlock_irqrestore(spinlock_t *lock,
126: unsigned long flags)
127: __releases(lock)
128: {
129: rt_spin_unlock(lock);
130: }
SourceFile:include/linux/spinlock_rt.h]
|
| 42/2 |
2026/05/18 03:08 |
llm |
expert |
0m
Model:
Tokens:
input: 36745
output: 45
thoughts: 565
Thoughts: **Analyzing the Kernel Stack Trace: A Deep Dive**
Okay, so I'm looking at this stack trace and trying to understand why I'm not seeing `rt_spin_unlock` in the trace, even though it's logically being called by `spin_unlock_irqrestore`. It hits me β `rt_spin_unlock` *isn't* inlined. However, because `spin_unlock_irqrestore` is `__always_inline`, it expands directly to a call to `rt_spin_unlock`, which then leads to `rt_mutex_slowunlock`. That's the path.
The clue here is that `rt_spin_unlock` might be *tail-called*. The compiler's optimization could skip the frame if this is a tail call.
Now, let's trace this back to the root issue. It seems `kbd_keycode` is calling `spin_unlock_irqrestore` on *some* lock. The question is, which one? Diving into the `kbd_keycode` function, I see this:
```c
1565: (*k_handler[type])(vc, KVAL(keysym), !down);
```
Okay, so the `k_handler` is a pointer to function array, and there's a reference to a lock there. Looking further up, that `k_handler` eventually calls `guard(spinlock_irqsave)(&func_buf_lock);`. Good, when `guard` goes out of scope, it calls `spin_unlock_irqrestore` on `&func_buf_lock`. Aha, `func_buf_lock` is a global spinlock. Why would that global spinlock appear to be inside a freed `tty_struct`? That's impossible.
Alright, back to `kbd_keycode` I go! There's a section involving `tty` inside an if statement. I see:
```c
1486: if (rep &&
1487: (!vc_kbd_mode(kbd, VC_REPEAT) ||
1488: (tty && !L_ECHO(tty) && tty_chars_in_buffer(tty)))) {
```
Interesting, `tty_chars_in_buffer` is called here. Now, that calls `tty->ops->chars_in_buffer(tty)`. This is where it gets interesting, as this calls a function pointer `tty->ops->chars_in_buffer(tty)`. The next thing to check is, what `chars_in_buffer` function is used for this `tty`. We need to investigate if this `tty` is a PTY, in which case we look for `pty_chars_in_buffer`, or if this `tty` is a VT (virtual terminal), we would be looking at `con_chars_in_buffer`. Also, the `tty` is actually `vc->port.tty`. This opens up a new set of possible issues. We'll start there.
|
| 43/2 |
2026/05/18 03:08 |
tool |
codesearch-definition-source |
0m
Error:
Args: map[ContextFile:drivers/tty/vt/vt.c IncludeLines:true Name:con_chars_in_buffer]
Results: map[SourceCode: SourceFile:]
|
| 44/2 |
2026/05/18 03:08 |
llm |
expert |
0m
Model:
Tokens:
input: 38031
output: 22
thoughts: 12
Thoughts: Here's a summary of my thought process:
**Diving into the Terminal Operations**
Alright, let's get down to brass tacks. My initial instinct is to zero in on the `tty_operations` structure. When dealing with Virtual Terminals (VT), this is where the core functionality resides. This structure dictates how the terminal interacts with the system, handling input, output, and control functions. I need to understand exactly how `tty_operations` handles the specifics of the VT implementation. My experience tells me that by examining this area I can uncover how the VT is integrated. I want to learn more about how VTs are managed by diving deep into the `tty_operations` structure. Let's see what we can find.
|
| 45/2 |
2026/05/18 03:09 |
tool |
grepper |
0m
Args: map[Expression:struct tty_operations con_ops]
Results: map[Output:drivers/tty/vt/vt.c=3909=console_initcall(con_init);
drivers/tty/vt/vt.c-3910-
drivers/tty/vt/vt.c:3911:static const struct tty_operations con_ops = {
drivers/tty/vt/vt.c-3912- .install = con_install,
]
|
| 46/2 |
2026/05/18 03:09 |
llm |
expert |
0m
Model:
Tokens:
input: 38325
output: 41
thoughts: 21
Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience:
**Diving into `vt.c`'s Connection Operations**
Okay, so I need to understand how the console operations are handled, specifically within the virtual terminal driver. I immediately think to check the `con_ops` structure definition, which I know is in `drivers/tty/vt/vt.c`. I'm going to jump in there to get a better grasp of the low-level functions dealing with things like character output, input, cursor control, and framebuffer interaction. I'm especially interested in how it hooks up with the underlying framebuffer or other display backends. From there, I can determine where I need to look for my particular interest, which will be dependent on my specific task. This will be my starting point.
|
| 47/2 |
2026/05/18 03:09 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/tty/vt/vt.c IncludeLines:true Name:con_ops]
Results: map[SourceCode:3911: static const struct tty_operations con_ops = {
3912: .install = con_install,
3913: .open = con_open,
3914: .close = con_close,
3915: .write = con_write,
3916: .write_room = con_write_room,
3917: .put_char = con_put_char,
3918: .flush_chars = con_flush_chars,
3919: .ioctl = vt_ioctl,
3920: #ifdef CONFIG_COMPAT
3921: .compat_ioctl = vt_compat_ioctl,
3922: #endif
3923: .stop = con_stop,
3924: .start = con_start,
3925: .throttle = con_throttle,
3926: .unthrottle = con_unthrottle,
3927: .resize = vt_resize,
3928: .shutdown = con_shutdown,
3929: .cleanup = con_cleanup,
3930: .ldisc_ok = con_ldisc_ok,
3931: };
SourceFile:drivers/tty/vt/vt.c]
|
| 48/2 |
2026/05/18 03:09 |
llm |
expert |
0m
Model:
Tokens:
input: 38902
output: 39
thoughts: 368
Thoughts: **Analyzing a Potential Use-After-Free Vulnerability**
Okay, so I'm looking at this report and immediately see something fishy. The initial trace pointed towards `con_ops` lacking `chars_in_buffer`, which meant `tty_chars_in_buffer` would return zero. My immediate thought was that this function, by returning zero, might bypass any lock acquisition since no actual data is being read from the tty.
But wait a minute, I have to be careful. Even if it *returns* zero, `tty_chars_in_buffer` still *accesses* `tty->ops->chars_in_buffer`. That's where the danger lies! If the `tty` structure is freed *before* that access, we're talking about a classic Use-After-Free (UAF) situation.
Now, the actual KASAN report specifies a UAF in `_raw_spin_lock_irqsave`. Interesting. The specific UAF is a "read of size 1" at a particular address. `_raw_spin_lock_irqsave`? That function is designed to read the spinlock. It reads the lock value to determine its state.
So, if the UAF is in `_raw_spin_lock_irqsave`, the likely UAF candidate is a spinlock *inside* the freed `tty_struct` structure. That's the part that's bothering me. Why would something like `kbd_keycode`βor anything else accessing `tty`βneed to lock a spinlock *within* the `tty_struct`? That seems strange. Let's get the definition of `tty_struct` and see what's actually there. I need to understand what's being accessed in the `tty_struct` so I can understand the vulnerability.
|
| 49/2 |
2026/05/18 03:09 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:include/linux/tty.h IncludeLines:true Name:tty_struct]
Results: map[SourceCode: 121: /**
122: * struct tty_struct - state associated with a tty while open
123: *
124: * @kref: reference counting by tty_kref_get() and tty_kref_put(), reaching zero
125: * frees the structure
126: * @dev: class device or %NULL (e.g. ptys, serdev)
127: * @driver: &struct tty_driver operating this tty
128: * @ops: &struct tty_operations of @driver for this tty (open, close, etc.)
129: * @index: index of this tty (e.g. to construct @name like tty12)
130: * @ldisc_sem: protects line discipline changes (@ldisc) -- lock tty not pty
131: * @ldisc: the current line discipline for this tty (n_tty by default)
132: * @atomic_write_lock: protects against concurrent writers, i.e. locks
133: * @write_cnt, @write_buf and similar
134: * @legacy_mutex: leftover from history (BKL -> BTM -> @legacy_mutex),
135: * protecting several operations on this tty
136: * @throttle_mutex: protects against concurrent tty_throttle_safe() and
137: * tty_unthrottle_safe() (but not tty_unthrottle())
138: * @termios_rwsem: protects @termios and @termios_locked
139: * @winsize_mutex: protects @winsize
140: * @termios: termios for the current tty, copied from/to @driver.termios
141: * @termios_locked: locked termios (by %TIOCGLCKTRMIOS and %TIOCSLCKTRMIOS
142: * ioctls)
143: * @name: name of the tty constructed by tty_line_name() (e.g. ttyS3)
144: * @flags: bitwise OR of %TTY_THROTTLED, %TTY_IO_ERROR, ...
145: * @count: count of open processes, reaching zero cancels all the work for
146: * this tty and drops a @kref too (but does not free this tty)
147: * @winsize: size of the terminal "window" (cf. @winsize_mutex)
148: * @flow: flow settings grouped together
149: * @flow.lock: lock for @flow members
150: * @flow.stopped: tty stopped/started by stop_tty()/start_tty()
151: * @flow.tco_stopped: tty stopped/started by %TCOOFF/%TCOON ioctls (it has
152: * precedence over @flow.stopped)
153: * @ctrl: control settings grouped together
154: * @ctrl.lock: lock for @ctrl members
155: * @ctrl.pgrp: process group of this tty (setpgrp(2))
156: * @ctrl.session: session of this tty (setsid(2)). Writes are protected by both
157: * @ctrl.lock and @legacy_mutex, readers must use at least one of
158: * them.
159: * @ctrl.pktstatus: packet mode status (bitwise OR of %TIOCPKT_ constants)
160: * @ctrl.packet: packet mode enabled
161: * @hw_stopped: not controlled by the tty layer, under @driver's control for CTS
162: * handling
163: * @receive_room: bytes permitted to feed to @ldisc without any being lost
164: * @flow_change: controls behavior of throttling, see tty_throttle_safe() and
165: * tty_unthrottle_safe()
166: * @link: link to another pty (master -> slave and vice versa)
167: * @fasync: state for %O_ASYNC (for %SIGIO); managed by fasync_helper()
168: * @write_wait: concurrent writers are waiting in this queue until they are
169: * allowed to write
170: * @read_wait: readers wait for data in this queue
171: * @hangup_work: normally a work to perform a hangup (do_tty_hangup()); while
172: * freeing the tty, (re)used to release_one_tty()
173: * @disc_data: pointer to @ldisc's private data (e.g. to &struct n_tty_data)
174: * @driver_data: pointer to @driver's private data (e.g. &struct uart_state)
175: * @files_lock: protects @tty_files list
176: * @tty_files: list of (re)openers of this tty (i.e. linked &struct
177: * tty_file_private)
178: * @closing: when set during close, n_tty processes only START & STOP chars
179: * @write_buf: temporary buffer used during tty_write() to copy user data to
180: * @write_cnt: count of bytes written in tty_write() to @write_buf
181: * @SAK_work: if the tty has a pending do_SAK, it is queued here
182: * @port: persistent storage for this device (i.e. &struct tty_port)
183: *
184: * All of the state associated with a tty while the tty is open. Persistent
185: * storage for tty devices is referenced here as @port and is documented in
186: * &struct tty_port.
187: */
188: struct tty_struct {
189: struct kref kref;
190: int index;
191: struct device *dev;
192: struct tty_driver *driver;
193: struct tty_port *port;
194: const struct tty_operations *ops;
195:
196: struct tty_ldisc *ldisc;
197: struct ld_semaphore ldisc_sem;
198:
199: struct mutex atomic_write_lock;
200: struct mutex legacy_mutex;
201: struct mutex throttle_mutex;
202: struct rw_semaphore termios_rwsem;
203: struct mutex winsize_mutex;
204: struct ktermios termios, termios_locked;
205: char name[64];
206: unsigned long flags;
207: int count;
208: unsigned int receive_room;
209: struct winsize winsize;
210:
211: struct {
212: spinlock_t lock;
213: bool stopped;
214: bool tco_stopped;
215: } flow;
216:
217: struct {
218: struct pid *pgrp;
219: struct pid *session;
220: spinlock_t lock;
221: unsigned char pktstatus;
222: bool packet;
223: } ctrl;
224:
225: bool hw_stopped;
226: bool closing;
227: int flow_change;
228:
229: struct tty_struct *link;
230: struct fasync_struct *fasync;
231: wait_queue_head_t write_wait;
232: wait_queue_head_t read_wait;
233: struct work_struct hangup_work;
234: void *disc_data;
235: void *driver_data;
236: spinlock_t files_lock;
237: int write_cnt;
238: u8 *write_buf;
239:
240: struct list_head tty_files;
241:
242: struct work_struct SAK_work;
243: } __randomize_layout;
SourceFile:include/linux/tty.h]
|
| 50/2 |
2026/05/18 03:09 |
llm |
expert |
0m
Model:
Tokens:
input: 42003
output: 21
thoughts: 185
Thoughts: **Analyzing Potential UAF in tty_chars_in_buffer**
Okay, I'm looking at this `tty_struct` again and immediately I see it has multiple locks β `flow.lock`, `ctrl.lock`, and `files_lock`. My immediate thought is, why isn't `tty_chars_in_buffer` using any of these?! That seems like a potential race condition and a possible Use-After-Free scenario. Let me double-check the code for `tty_chars_in_buffer`.
Right, it just does a function pointer dereference:
```c
unsigned int tty_chars_in_buffer(struct tty_struct *tty)
{
if (tty->ops->chars_in_buffer)
return tty->ops->chars_in_buffer(tty);
return 0;
}
```
Okay, if that `tty` structure gets freed while this function is running, `tty->ops` will be reading from freed memory. That could be bad. Wait, the UAF read is at `ffff888051204418`. I should probably verify what the offset of `ops` is within the `tty_struct` to confirm this potential vulnerability.
|
| 51/2 |
2026/05/18 03:09 |
tool |
codesearch-struct-layout |
0m
Args:
Results: map[Fields:[map[Name:kref OffsetBits:0 SizeBits:32] map[Name:index OffsetBits:32 SizeBits:32] map[Name:dev OffsetBits:64 SizeBits:64] map[Name:driver OffsetBits:128 SizeBits:64] map[Name:port OffsetBits:192 SizeBits:64] map[Name:ops OffsetBits:256 SizeBits:64] map[Name:ldisc OffsetBits:320 SizeBits:64] map[Name:ldisc_sem OffsetBits:384 SizeBits:1216] map[Name:atomic_write_lock OffsetBits:1600 SizeBits:1024] map[Name:legacy_mutex OffsetBits:2624 SizeBits:1024] map[Name:throttle_mutex OffsetBits:3648 SizeBits:1024] map[Name:termios_rwsem OffsetBits:4672 SizeBits:1088] map[Name:winsize_mutex OffsetBits:5760 SizeBits:1024] map[Name:termios OffsetBits:6784 SizeBits:352] map[Name:termios_locked OffsetBits:7136 SizeBits:352] map[Name:name OffsetBits:7488 SizeBits:512] map[Name:flags OffsetBits:8000 SizeBits:64] map[Name:count OffsetBits:8064 SizeBits:32] map[Name:receive_room OffsetBits:8096 SizeBits:32] map[Name:winsize OffsetBits:8128 SizeBits:64] map[Name:flow OffsetBits:8192 SizeBits:1088] map[Name:ctrl OffsetBits:9280 SizeBits:1216] map[Name:hw_stopped OffsetBits:10496 SizeBits:8] map[Name:closing OffsetBits:10504 SizeBits:8] map[Name:flow_change OffsetBits:10528 SizeBits:32] map[Name:link OffsetBits:10560 SizeBits:64] map[Name:fasync OffsetBits:10624 SizeBits:64] map[Name:write_wait OffsetBits:10688 SizeBits:1152] map[Name:read_wait OffsetBits:11840 SizeBits:1152] map[Name:hangup_work OffsetBits:12992 SizeBits:576] map[Name:disc_data OffsetBits:13568 SizeBits:64] map[Name:driver_data OffsetBits:13632 SizeBits:64] map[Name:files_lock OffsetBits:13696 SizeBits:1024] map[Name:write_cnt OffsetBits:14720 SizeBits:32] map[Name:write_buf OffsetBits:14784 SizeBits:64] map[Name:tty_files OffsetBits:14848 SizeBits:128] map[Name:SAK_work OffsetBits:14976 SizeBits:576]]]
|
| 52/2 |
2026/05/18 03:09 |
llm |
expert |
0m
Model:
Tokens:
input: 43318
output: 43
thoughts: 509
Thoughts: **Analyzing the `tty_struct` Vulnerability**
Okay, so the `tty_struct` has this `__randomize_layout` flag, meaning the offsets are randomized. That's a key detail. The problematic address is `ffff888051204418`, which is `ffff888051204000 + 1048`. Hmm, 1048 bytes equals 8384 bits. In a non-randomized scenario, that offset would point to something like `flow` or `ctrl`, but with randomization, it could be anything.
The UAF (use-after-free) is happening in `_raw_spin_lock_irqsave`. The stack trace reveals: `rt_mutex_slowunlock` calling `raw_spin_lock_irqsave(&lock->wait_lock, flags)`. And `lock` is a `struct rt_mutex_base` pointer. I'm following. Now, `rt_mutex_slowunlock` is called by `rt_spin_unlock` which is called by `spin_unlock_irqrestore`. If `spin_unlock_irqrestore` is called on a spinlock *within* `tty_struct`, then `lock` points to that spinlock!
I need to figure out which spinlock in `tty_struct` is being unlocked when `kbd_keycode` is involved. Let me re-examine `kbd_keycode`. Hold on, `kbd_keycode` itself doesn't directly unlock any spinlocks inside `tty_struct`. But! It *does* call `tty_chars_in_buffer(tty)`. Okay, so `tty_chars_in_buffer` then calls `tty->ops->chars_in_buffer(tty)`. Now we're getting somewhere. What if the `tty->ops->chars_in_buffer` is actually the `pty_chars_in_buffer` function? That could be it!
|
| 53/2 |
2026/05/18 03:09 |
tool |
codesearch-definition-source |
0m
Error:
Args: map[ContextFile:drivers/tty/pty.c IncludeLines:true Name:pty_chars_in_buffer]
Results: map[SourceCode: SourceFile:]
|
| 54/2 |
2026/05/18 03:09 |
llm |
expert |
0m
Model:
Tokens:
input: 44321
output: 19
thoughts: 14
Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience:
**Debugging a Potential I/O Bottleneck**
Okay, so I'm troubleshooting, and my initial hunch is pointing towards a potential bottleneck in the data flow, particularly when writing to a pseudo-terminal. I'm thinking, "Let's zero in on a likely suspect: the `pty_write_room` function (or something similar in our codebase)." It's the point where data is queued up for writing to the underlying terminal, and issues here can cascade. I'm immediately picturing the potential interactions - are we waiting on the terminal to accept data? Is there a buffer overrun issue? Is the locking around this resource too aggressive? I'm going to start there and see what the code says.
|
| 55/2 |
2026/05/18 03:09 |
tool |
grepper |
0m
Args: map[Expression:chars_in_buffer]
Results: map[Output:
Full output is too long, showing 500 out of 882 lines.
Use more precise expression if possible.
[arch/um/drivers/line.c=50=unsigned int line_write_room(struct tty_struct *tty)
--
arch/um/drivers/line.c-62-
arch/um/drivers/line.c:63:unsigned int line_chars_in_buffer(struct tty_struct *tty)
arch/um/drivers/line.c-64-{
--
arch/um/drivers/line.h=67=extern ssize_t line_write(struct tty_struct *tty, const u8 *buf, size_t len);
arch/um/drivers/line.h:68:extern unsigned int line_chars_in_buffer(struct tty_struct *tty);
arch/um/drivers/line.h-69-extern void line_flush_buffer(struct tty_struct *tty);
--
arch/um/drivers/ssl.c=92=static const struct tty_operations ssl_ops = {
--
arch/um/drivers/ssl.c-96- .write_room = line_write_room,
arch/um/drivers/ssl.c:97: .chars_in_buffer = line_chars_in_buffer,
arch/um/drivers/ssl.c-98- .flush_buffer = line_flush_buffer,
--
arch/um/drivers/stdio_console.c=98=static const struct tty_operations console_ops = {
--
arch/um/drivers/stdio_console.c-103- .write_room = line_write_room,
arch/um/drivers/stdio_console.c:104: .chars_in_buffer = line_chars_in_buffer,
arch/um/drivers/stdio_console.c-105- .flush_buffer = line_flush_buffer,
--
drivers/ipack/devices/ipoctal.c=482=static unsigned int ipoctal_write_room(struct tty_struct *tty)
--
drivers/ipack/devices/ipoctal.c-488-
drivers/ipack/devices/ipoctal.c:489:static unsigned int ipoctal_chars_in_buffer(struct tty_struct *tty)
drivers/ipack/devices/ipoctal.c-490-{
--
drivers/ipack/devices/ipoctal.c=671=static const struct tty_operations ipoctal_fops = {
--
drivers/ipack/devices/ipoctal.c-678- .write_room = ipoctal_write_room,
drivers/ipack/devices/ipoctal.c:679: .chars_in_buffer = ipoctal_chars_in_buffer,
drivers/ipack/devices/ipoctal.c-680- .get_icount = ipoctal_get_icount,
--
drivers/mmc/core/sdio_uart.c=782=static unsigned int sdio_uart_write_room(struct tty_struct *tty)
--
drivers/mmc/core/sdio_uart.c-787-
drivers/mmc/core/sdio_uart.c:788:static unsigned int sdio_uart_chars_in_buffer(struct tty_struct *tty)
drivers/mmc/core/sdio_uart.c-789-{
--
drivers/mmc/core/sdio_uart.c=997=static const struct tty_operations sdio_uart_ops = {
--
drivers/mmc/core/sdio_uart.c-1001- .write_room = sdio_uart_write_room,
drivers/mmc/core/sdio_uart.c:1002: .chars_in_buffer = sdio_uart_chars_in_buffer,
drivers/mmc/core/sdio_uart.c-1003- .send_xchar = sdio_uart_send_xchar,
--
drivers/net/slip/slip.c=465=static void sl_tx_timeout(struct net_device *dev, unsigned int txqueue)
--
drivers/net/slip/slip.c-484- dev->name,
drivers/net/slip/slip.c:485: (tty_chars_in_buffer(sl->tty) || sl->xleft) ?
drivers/net/slip/slip.c-486- "bad line quality" : "driver error");
--
drivers/net/usb/hso.c=1374=static void hso_serial_set_termios(struct tty_struct *tty,
--
drivers/net/usb/hso.c-1396-/* how many characters in the buffer */
drivers/net/usb/hso.c:1397:static unsigned int hso_serial_chars_in_buffer(struct tty_struct *tty)
drivers/net/usb/hso.c-1398-{
--
drivers/net/usb/hso.c=3168=static const struct tty_operations hso_serial_ops = {
--
drivers/net/usb/hso.c-3175- .set_termios = hso_serial_set_termios,
drivers/net/usb/hso.c:3176: .chars_in_buffer = hso_serial_chars_in_buffer,
drivers/net/usb/hso.c-3177- .tiocmget = hso_serial_tiocmget,
--
drivers/s390/char/con3215.c=1042=static void tty3215_flush_chars(struct tty_struct *tty)
--
drivers/s390/char/con3215.c-1048- */
drivers/s390/char/con3215.c:1049:static unsigned int tty3215_chars_in_buffer(struct tty_struct *tty)
drivers/s390/char/con3215.c-1050-{
--
drivers/s390/char/con3215.c=1116=static const struct tty_operations tty3215_ops = {
--
drivers/s390/char/con3215.c-1123- .write_room = tty3215_write_room,
drivers/s390/char/con3215.c:1124: .chars_in_buffer = tty3215_chars_in_buffer,
drivers/s390/char/con3215.c-1125- .flush_buffer = tty3215_flush_buffer,
--
drivers/s390/char/sclp_con.c=160=sclp_console_write(struct console *console, const char *message,
--
drivers/s390/char/sclp_con.c-207- /* Setup timer to output current console buffer after 1/10 second */
drivers/s390/char/sclp_con.c:208: if (sclp_conbuf != NULL && sclp_chars_in_buffer(sclp_conbuf) != 0 &&
drivers/s390/char/sclp_con.c-209- !timer_pending(&sclp_con_timer)) {
--
drivers/s390/char/sclp_rw.c=321=unsigned int
drivers/s390/char/sclp_rw.c:322:sclp_chars_in_buffer(struct sclp_buffer *buffer)
drivers/s390/char/sclp_rw.c-323-{
--
drivers/s390/char/sclp_rw.h=88=int sclp_emit_buffer(struct sclp_buffer *,void (*)(struct sclp_buffer *,int));
drivers/s390/char/sclp_rw.h:89:unsigned int sclp_chars_in_buffer(struct sclp_buffer *);
drivers/s390/char/sclp_rw.h-90-
--
drivers/s390/char/sclp_tty.c=171=static int sclp_tty_write_string(const u8 *str, int count, int may_fail)
--
drivers/s390/char/sclp_tty.c-217- /* Setup timer to output current console buffer after 1/10 second */
drivers/s390/char/sclp_tty.c:218: if (sclp_ttybuf && sclp_chars_in_buffer(sclp_ttybuf) &&
drivers/s390/char/sclp_tty.c-219- !timer_pending(&sclp_tty_timer)) {
--
drivers/s390/char/sclp_tty.c=283=static unsigned int
drivers/s390/char/sclp_tty.c:284:sclp_tty_chars_in_buffer(struct tty_struct *tty)
drivers/s390/char/sclp_tty.c-285-{
--
drivers/s390/char/sclp_tty.c-291- if (sclp_ttybuf != NULL)
drivers/s390/char/sclp_tty.c:292: count = sclp_chars_in_buffer(sclp_ttybuf);
drivers/s390/char/sclp_tty.c-293- list_for_each_entry(t, &sclp_tty_outqueue, list) {
drivers/s390/char/sclp_tty.c:294: count += sclp_chars_in_buffer(t);
drivers/s390/char/sclp_tty.c-295- }
--
drivers/s390/char/sclp_tty.c=482=static const struct tty_operations sclp_ops = {
--
drivers/s390/char/sclp_tty.c-488- .write_room = sclp_tty_write_room,
drivers/s390/char/sclp_tty.c:489: .chars_in_buffer = sclp_tty_chars_in_buffer,
drivers/s390/char/sclp_tty.c-490- .flush_buffer = sclp_tty_flush_buffer,
--
drivers/s390/char/sclp_vt220.c=626=static unsigned int
drivers/s390/char/sclp_vt220.c:627:sclp_vt220_chars_in_buffer(struct tty_struct *tty)
drivers/s390/char/sclp_vt220.c-628-{
--
drivers/s390/char/sclp_vt220.c=713=static const struct tty_operations sclp_vt220_ops = {
--
drivers/s390/char/sclp_vt220.c-719- .write_room = sclp_vt220_write_room,
drivers/s390/char/sclp_vt220.c:720: .chars_in_buffer = sclp_vt220_chars_in_buffer,
drivers/s390/char/sclp_vt220.c-721- .flush_buffer = sclp_vt220_flush_buffer,
--
drivers/staging/greybus/uart.c=442=static unsigned int gb_tty_write_room(struct tty_struct *tty)
--
drivers/staging/greybus/uart.c-458-
drivers/staging/greybus/uart.c:459:static unsigned int gb_tty_chars_in_buffer(struct tty_struct *tty)
drivers/staging/greybus/uart.c-460-{
--
drivers/staging/greybus/uart.c=776=static const struct tty_operations gb_ops = {
--
drivers/staging/greybus/uart.c-786- .unthrottle = gb_tty_unthrottle,
drivers/staging/greybus/uart.c:787: .chars_in_buffer = gb_tty_chars_in_buffer,
drivers/staging/greybus/uart.c-788- .break_ctl = gb_tty_break_ctl,
--
drivers/tty/amiserial.c=785=static unsigned int rs_write_room(struct tty_struct *tty)
--
drivers/tty/amiserial.c-791-
drivers/tty/amiserial.c:792:static unsigned int rs_chars_in_buffer(struct tty_struct *tty)
drivers/tty/amiserial.c-793-{
--
drivers/tty/amiserial.c=1428=static const struct tty_operations serial_ops = {
--
drivers/tty/amiserial.c-1434- .write_room = rs_write_room,
drivers/tty/amiserial.c:1435: .chars_in_buffer = rs_chars_in_buffer,
drivers/tty/amiserial.c-1436- .flush_buffer = rs_flush_buffer,
--
drivers/tty/ehv_bytechan.c=590=static void ehv_bc_tty_hangup(struct tty_struct *ttys)
--
drivers/tty/ehv_bytechan.c-602- * at least how big the TX buffers are, then we could implement the
drivers/tty/ehv_bytechan.c:603: * .wait_until_sent and .chars_in_buffer functions.
drivers/tty/ehv_bytechan.c-604- */
--
drivers/tty/goldfish.c=188=static unsigned int goldfish_tty_write_room(struct tty_struct *tty)
--
drivers/tty/goldfish.c-192-
drivers/tty/goldfish.c:193:static unsigned int goldfish_tty_chars_in_buffer(struct tty_struct *tty)
drivers/tty/goldfish.c-194-{
--
drivers/tty/goldfish.c=227=static const struct tty_operations goldfish_tty_ops = {
--
drivers/tty/goldfish.c-232- .write_room = goldfish_tty_write_room,
drivers/tty/goldfish.c:233: .chars_in_buffer = goldfish_tty_chars_in_buffer,
drivers/tty/goldfish.c-234-};
--
drivers/tty/hvc/hvc_console.c=389=static void hvc_close(struct tty_struct *tty, struct file * filp)
--
drivers/tty/hvc/hvc_console.c-417- /*
drivers/tty/hvc/hvc_console.c:418: * Chain calls chars_in_buffer() and returns immediately if
drivers/tty/hvc/hvc_console.c-419- * there is no buffered data otherwise sleeps on a wait queue
drivers/tty/hvc/hvc_console.c:420: * waking periodically to check chars_in_buffer().
drivers/tty/hvc/hvc_console.c-421- */
--
drivers/tty/hvc/hvc_console.c=589=static unsigned int hvc_write_room(struct tty_struct *tty)
--
drivers/tty/hvc/hvc_console.c-598-
drivers/tty/hvc/hvc_console.c:599:static unsigned int hvc_chars_in_buffer(struct tty_struct *tty)
drivers/tty/hvc/hvc_console.c-600-{
--
drivers/tty/hvc/hvc_console.c=888=static const struct tty_operations hvc_ops = {
--
drivers/tty/hvc/hvc_console.c-896- .write_room = hvc_write_room,
drivers/tty/hvc/hvc_console.c:897: .chars_in_buffer = hvc_chars_in_buffer,
drivers/tty/hvc/hvc_console.c-898- .tiocmget = hvc_tiocmget,
--
drivers/tty/hvc/hvcs.c-113- * an hvcs_close(). Removed spinlock protection of hvcs_struct data members in
drivers/tty/hvc/hvcs.c:114: * hvcs_write_room() and hvcs_chars_in_buffer() because they aren't needed.
drivers/tty/hvc/hvcs.c-115- */
--
drivers/tty/hvc/hvcs.c=250=struct hvcs_struct {
--
drivers/tty/hvc/hvcs.c-274- char buffer[HVCS_BUFF_LEN];
drivers/tty/hvc/hvcs.c:275: int chars_in_buffer;
drivers/tty/hvc/hvcs.c-276-
--
drivers/tty/hvc/hvcs.c=525=static void hvcs_try_write(struct hvcs_struct *hvcsd)
--
drivers/tty/hvc/hvcs.c-534- &hvcsd->buffer[0],
drivers/tty/hvc/hvcs.c:535: hvcsd->chars_in_buffer );
drivers/tty/hvc/hvcs.c-536- if (sent > 0) {
drivers/tty/hvc/hvcs.c:537: hvcsd->chars_in_buffer = 0;
drivers/tty/hvc/hvcs.c-538- /* wmb(); */
--
drivers/tty/hvc/hvcs.c=726=static int hvcs_probe(
--
drivers/tty/hvc/hvcs.c-764- /* hvcsd->index = ++hvcs_struct_count; */
drivers/tty/hvc/hvcs.c:765: hvcsd->chars_in_buffer = 0;
drivers/tty/hvc/hvcs.c-766- hvcsd->todo_mask = 0;
--
drivers/tty/hvc/hvcs.c=1220=static void hvcs_hangup(struct tty_struct * tty)
--
drivers/tty/hvc/hvcs.c-1241- memset(&hvcsd->buffer[0], 0x00, HVCS_BUFF_LEN);
drivers/tty/hvc/hvcs.c:1242: hvcsd->chars_in_buffer = 0;
drivers/tty/hvc/hvcs.c-1243-
--
drivers/tty/hvc/hvcs.c=1258=static ssize_t hvcs_write(struct tty_struct *tty, const u8 *buf, size_t count)
--
drivers/tty/hvc/hvcs.c-1300- tosend = min_t(size_t, count,
drivers/tty/hvc/hvcs.c:1301: (HVCS_BUFF_LEN - hvcsd->chars_in_buffer));
drivers/tty/hvc/hvcs.c-1302- /*
--
drivers/tty/hvc/hvcs.c-1308-
drivers/tty/hvc/hvcs.c:1309: memcpy(&hvcsd->buffer[hvcsd->chars_in_buffer],
drivers/tty/hvc/hvcs.c-1310- &charbuf[total_sent],
--
drivers/tty/hvc/hvcs.c-1312-
drivers/tty/hvc/hvcs.c:1313: hvcsd->chars_in_buffer += tosend;
drivers/tty/hvc/hvcs.c-1314-
--
drivers/tty/hvc/hvcs.c-1325- &hvcsd->buffer[0],
drivers/tty/hvc/hvcs.c:1326: hvcsd->chars_in_buffer);
drivers/tty/hvc/hvcs.c-1327-
--
drivers/tty/hvc/hvcs.c-1340-
drivers/tty/hvc/hvcs.c:1341: hvcsd->chars_in_buffer = 0;
drivers/tty/hvc/hvcs.c-1342- /*
drivers/tty/hvc/hvcs.c:1343: * Test after the chars_in_buffer reset otherwise this could
drivers/tty/hvc/hvcs.c-1344- * deadlock our writes if hvc_put_chars fails.
--
drivers/tty/hvc/hvcs.c=1363=static unsigned int hvcs_write_room(struct tty_struct *tty)
--
drivers/tty/hvc/hvcs.c-1369-
drivers/tty/hvc/hvcs.c:1370: return HVCS_BUFF_LEN - hvcsd->chars_in_buffer;
drivers/tty/hvc/hvcs.c-1371-}
drivers/tty/hvc/hvcs.c-1372-
drivers/tty/hvc/hvcs.c:1373:static unsigned int hvcs_chars_in_buffer(struct tty_struct *tty)
drivers/tty/hvc/hvcs.c-1374-{
--
drivers/tty/hvc/hvcs.c-1376-
drivers/tty/hvc/hvcs.c:1377: return hvcsd->chars_in_buffer;
drivers/tty/hvc/hvcs.c-1378-}
--
drivers/tty/hvc/hvcs.c=1380=static const struct tty_operations hvcs_ops = {
--
drivers/tty/hvc/hvcs.c-1387- .write_room = hvcs_write_room,
drivers/tty/hvc/hvcs.c:1388: .chars_in_buffer = hvcs_chars_in_buffer,
drivers/tty/hvc/hvcs.c-1389- .unthrottle = hvcs_unthrottle,
--
drivers/tty/hvc/hvsi.c=58=struct hvsi_struct {
--
drivers/tty/hvc/hvsi.c-66- uint8_t throttle_buf[128];
drivers/tty/hvc/hvsi.c:67: uint8_t outbuf[N_OUTBUF]; /* to implement write_room and chars_in_buffer */
drivers/tty/hvc/hvsi.c-68- /* inbuf is for packet reassembly. leave a little room for leftovers. */
--
drivers/tty/hvc/hvsi.c=893=static unsigned int hvsi_write_room(struct tty_struct *tty)
--
drivers/tty/hvc/hvsi.c-899-
drivers/tty/hvc/hvsi.c:900:static unsigned int hvsi_chars_in_buffer(struct tty_struct *tty)
drivers/tty/hvc/hvsi.c-901-{
--
drivers/tty/hvc/hvsi.c=1025=static const struct tty_operations hvsi_ops = {
--
drivers/tty/hvc/hvsi.c-1030- .write_room = hvsi_write_room,
drivers/tty/hvc/hvsi.c:1031: .chars_in_buffer = hvsi_chars_in_buffer,
drivers/tty/hvc/hvsi.c-1032- .throttle = hvsi_throttle,
--
drivers/tty/ipwireless/tty.c=266=static int ipwireless_set_serial_info(struct tty_struct *linux_tty,
--
drivers/tty/ipwireless/tty.c-271-
drivers/tty/ipwireless/tty.c:272:static unsigned int ipw_chars_in_buffer(struct tty_struct *linux_tty)
drivers/tty/ipwireless/tty.c-273-{
--
drivers/tty/ipwireless/tty.c=549=static const struct tty_operations tty_ops = {
--
drivers/tty/ipwireless/tty.c-555- .ioctl = ipw_ioctl,
drivers/tty/ipwireless/tty.c:556: .chars_in_buffer = ipw_chars_in_buffer,
drivers/tty/ipwireless/tty.c-557- .tiocmget = ipw_tiocmget,
--
drivers/tty/mips_ejtag_fdc.c=84=struct mips_ejtag_fdc_tty;
--
drivers/tty/mips_ejtag_fdc.c-95- * This protects between user context and kernel thread.
drivers/tty/mips_ejtag_fdc.c:96: * It is used from chars_in_buffer()/write_room() TTY
drivers/tty/mips_ejtag_fdc.c-97- * callbacks which are used during wait operations, so a
--
drivers/tty/mips_ejtag_fdc.c=844=static unsigned int mips_ejtag_fdc_tty_write_room(struct tty_struct *tty)
--
drivers/tty/mips_ejtag_fdc.c-857-
drivers/tty/mips_ejtag_fdc.c:858:static unsigned int mips_ejtag_fdc_tty_chars_in_buffer(struct tty_struct *tty)
drivers/tty/mips_ejtag_fdc.c-859-{
--
drivers/tty/mips_ejtag_fdc.c=871=static const struct tty_operations mips_ejtag_fdc_tty_ops = {
--
drivers/tty/mips_ejtag_fdc.c-877- .write_room = mips_ejtag_fdc_tty_write_room,
drivers/tty/mips_ejtag_fdc.c:878: .chars_in_buffer = mips_ejtag_fdc_tty_chars_in_buffer,
drivers/tty/mips_ejtag_fdc.c-879-};
--
drivers/tty/moxa.c=435=static void moxa_flush_buffer(struct tty_struct *);
drivers/tty/moxa.c:436:static unsigned int moxa_chars_in_buffer(struct tty_struct *);
drivers/tty/moxa.c-437-static void moxa_set_termios(struct tty_struct *, const struct ktermios *);
--
drivers/tty/moxa.c=533=static const struct tty_operations moxa_ops = {
--
drivers/tty/moxa.c-538- .flush_buffer = moxa_flush_buffer,
drivers/tty/moxa.c:539: .chars_in_buffer = moxa_chars_in_buffer,
drivers/tty/moxa.c-540- .set_termios = moxa_set_termios,
--
drivers/tty/moxa.c=1283=static void moxa_flush_buffer(struct tty_struct *tty)
--
drivers/tty/moxa.c-1292-
drivers/tty/moxa.c:1293:static unsigned int moxa_chars_in_buffer(struct tty_struct *tty)
drivers/tty/moxa.c-1294-{
--
drivers/tty/mxser.c=928=static unsigned int mxser_write_room(struct tty_struct *tty)
--
drivers/tty/mxser.c-934-
drivers/tty/mxser.c:935:static unsigned int mxser_chars_in_buffer(struct tty_struct *tty)
drivers/tty/mxser.c-936-{
--
drivers/tty/mxser.c=1638=static const struct tty_operations mxser_ops = {
--
drivers/tty/mxser.c-1644- .write_room = mxser_write_room,
drivers/tty/mxser.c:1645: .chars_in_buffer = mxser_chars_in_buffer,
drivers/tty/mxser.c-1646- .flush_buffer = mxser_flush_buffer,
--
drivers/tty/n_gsm.c=4413=static unsigned int gsmtty_write_room(struct tty_struct *tty)
--
drivers/tty/n_gsm.c-4420-
drivers/tty/n_gsm.c:4421:static unsigned int gsmtty_chars_in_buffer(struct tty_struct *tty)
drivers/tty/n_gsm.c-4422-{
--
drivers/tty/n_gsm.c=4446=static void gsmtty_wait_until_sent(struct tty_struct *tty, int timeout)
--
drivers/tty/n_gsm.c-4448- /* The FIFO handles the queue so the kernel will do the right
drivers/tty/n_gsm.c:4449: thing waiting on chars_in_buffer before calling us. No work
drivers/tty/n_gsm.c-4450- to do here */
--
drivers/tty/n_gsm.c=4600=static const struct tty_operations gsmtty_ops = {
--
drivers/tty/n_gsm.c-4605- .write_room = gsmtty_write_room,
drivers/tty/n_gsm.c:4606: .chars_in_buffer = gsmtty_chars_in_buffer,
drivers/tty/n_gsm.c-4607- .flush_buffer = gsmtty_flush_buffer,
--
drivers/tty/n_hdlc.c=580=static int n_hdlc_tty_ioctl(struct tty_struct *tty, unsigned int cmd,
--
drivers/tty/n_hdlc.c-604- /* get the pending tx byte count in the driver */
drivers/tty/n_hdlc.c:605: count = tty_chars_in_buffer(tty);
drivers/tty/n_hdlc.c-606- /* add size of next output frame in queue */
--
drivers/tty/n_tty.c=193=static void n_tty_kick_worker(const struct tty_struct *tty)
--
drivers/tty/n_tty.c-212-
drivers/tty/n_tty.c:213:static ssize_t chars_in_buffer(const struct tty_struct *tty)
drivers/tty/n_tty.c-214-{
--
drivers/tty/n_tty.c=255=static void n_tty_check_unthrottle(struct tty_struct *tty)
--
drivers/tty/n_tty.c-257- if (tty->driver->type == TTY_DRIVER_TYPE_PTY) {
drivers/tty/n_tty.c:258: if (chars_in_buffer(tty) > TTY_THRESHOLD_UNTHROTTLE)
drivers/tty/n_tty.c-259- return;
--
drivers/tty/n_tty.c-265- /* If there is enough space in the read buffer now, let the
drivers/tty/n_tty.c:266: * low-level driver know. We use chars_in_buffer() to
drivers/tty/n_tty.c-267- * check the buffer, as it now knows about canonical mode.
--
drivers/tty/n_tty.c-274- tty_set_flow_change(tty, TTY_UNTHROTTLE_SAFE);
drivers/tty/n_tty.c:275: if (chars_in_buffer(tty) > TTY_THRESHOLD_UNTHROTTLE)
drivers/tty/n_tty.c-276- break;
--
drivers/tty/n_tty.c=1671=n_tty_receive_buf_common(struct tty_struct *tty, const u8 *cp, const u8 *fp,
--
drivers/tty/n_tty.c-1738- * Barrier here is to ensure to read the latest read_tail in
drivers/tty/n_tty.c:1739: * chars_in_buffer() and to make sure that read_tail is not loaded
drivers/tty/n_tty.c-1740- * before ldata->no_room is set.
--
drivers/tty/n_tty.c-1742- smp_mb();
drivers/tty/n_tty.c:1743: if (!chars_in_buffer(tty))
drivers/tty/n_tty.c-1744- n_tty_kick_worker(tty);
--
drivers/tty/n_tty.c=2433=static __poll_t n_tty_poll(struct tty_struct *tty, struct file *file,
--
drivers/tty/n_tty.c-2453- if (tty->ops->write && !tty_is_writelocked(tty) &&
drivers/tty/n_tty.c:2454: tty_chars_in_buffer(tty) < WAKEUP_CHARS &&
drivers/tty/n_tty.c-2455- tty_write_room(tty) > 0)
--
drivers/tty/n_tty.c=2479=static int n_tty_ioctl(struct tty_struct *tty, unsigned int cmd,
--
drivers/tty/n_tty.c-2486- case TIOCOUTQ:
drivers/tty/n_tty.c:2487: return put_user(tty_chars_in_buffer(tty), (int __user *) arg);
drivers/tty/n_tty.c-2488- case TIOCINQ:
--
drivers/tty/nozomi.c=1752=static void ntty_throttle(struct tty_struct *tty)
--
drivers/tty/nozomi.c-1762-/* Returns number of chars in buffer, called by tty layer */
drivers/tty/nozomi.c:1763:static unsigned int ntty_chars_in_buffer(struct tty_struct *tty)
drivers/tty/nozomi.c-1764-{
--
drivers/tty/nozomi.c=1779=static const struct tty_operations tty_ops = {
--
drivers/tty/nozomi.c-1787- .throttle = ntty_throttle,
drivers/tty/nozomi.c:1788: .chars_in_buffer = ntty_chars_in_buffer,
drivers/tty/nozomi.c-1789- .tiocmget = ntty_tiocmget,
--
drivers/tty/serial/serial_core.c=638=static unsigned int uart_write_room(struct tty_struct *tty)
--
drivers/tty/serial/serial_core.c-653-
drivers/tty/serial/serial_core.c:654:static unsigned int uart_chars_in_buffer(struct tty_struct *tty)
drivers/tty/serial/serial_core.c-655-{
--
drivers/tty/serial/serial_core.c=2653=static const struct tty_operations uart_ops = {
--
drivers/tty/serial/serial_core.c-2660- .write_room = uart_write_room,
drivers/tty/serial/serial_core.c:2661: .chars_in_buffer= uart_chars_in_buffer,
drivers/tty/serial/serial_core.c-2662- .flush_buffer = uart_flush_buffer,
--
drivers/tty/synclink_gt.c=1233=static int synclink_gt_proc_show(struct seq_file *m, void *v)
--
drivers/tty/synclink_gt.c-1249- */
drivers/tty/synclink_gt.c:1250:static unsigned int chars_in_buffer(struct tty_struct *tty)
drivers/tty/synclink_gt.c-1251-{
--
drivers/tty/synclink_gt.c-1253- unsigned int count;
drivers/tty/synclink_gt.c:1254: if (sanity_check(info, tty->name, "chars_in_buffer"))
drivers/tty/synclink_gt.c-1255- return 0;
drivers/tty/synclink_gt.c-1256- count = tbuf_bytes(info);
drivers/tty/synclink_gt.c:1257: DBGINFO(("%s chars_in_buffer()=%u\n", info->device_name, count));
drivers/tty/synclink_gt.c-1258- return count;
--
drivers/tty/synclink_gt.c=3601=static const struct tty_operations ops = {
--
drivers/tty/synclink_gt.c-3607- .write_room = write_room,
drivers/tty/synclink_gt.c:3608: .chars_in_buffer = chars_in_buffer,
drivers/tty/synclink_gt.c-3609- .flush_buffer = flush_buffer,
--
drivers/tty/tty_ioctl.c-41-/**
drivers/tty/tty_ioctl.c:42: * tty_chars_in_buffer - characters pending
drivers/tty/tty_ioctl.c-43- * @tty: terminal
--
drivers/tty/tty_ioctl.c-47- */
drivers/tty/tty_ioctl.c:48:unsigned int tty_chars_in_buffer(struct tty_struct *tty)
drivers/tty/tty_ioctl.c-49-{
drivers/tty/tty_ioctl.c:50: if (tty->ops->chars_in_buffer)
drivers/tty/tty_ioctl.c:51: return tty->ops->chars_in_buffer(tty);
drivers/tty/tty_ioctl.c-52- return 0;
drivers/tty/tty_ioctl.c-53-}
drivers/tty/tty_ioctl.c:54:EXPORT_SYMBOL(tty_chars_in_buffer);
drivers/tty/tty_ioctl.c-55-
--
drivers/tty/tty_ioctl.c=179=void tty_wait_until_sent(struct tty_struct *tty, long timeout)
--
drivers/tty/tty_ioctl.c-184- timeout = wait_event_interruptible_timeout(tty->write_wait,
drivers/tty/tty_ioctl.c:185: !tty_chars_in_buffer(tty), timeout);
drivers/tty/tty_ioctl.c-186- if (timeout <= 0)
--
drivers/tty/tty_ioctl.c=444=static int set_termios(struct tty_struct *tty, void __user *arg, int opt)
--
drivers/tty/tty_ioctl.c-483-retry_write_wait:
drivers/tty/tty_ioctl.c:484: retval = wait_event_interruptible(tty->write_wait, !tty_chars_in_buffer(tty));
drivers/tty/tty_ioctl.c-485- if (retval < 0)
--
drivers/tty/tty_ioctl.c-491- /* Racing writer? */
drivers/tty/tty_ioctl.c:492: if (tty_chars_in_buffer(tty)) {
drivers/tty/tty_ioctl.c-493- tty_write_unlock(tty);
--
drivers/tty/vcc.c=22=struct vcc_port {
--
drivers/tty/vcc.c-38- */
drivers/tty/vcc.c:39: size_t chars_in_buffer;
drivers/tty/vcc.c-40- struct vio_vcc buffer;
--
drivers/tty/vcc.c=383=static void vcc_tx_timer(struct timer_list *t)
--
drivers/tty/vcc.c-396-
drivers/tty/vcc.c:397: tosend = min(VCC_BUFF_LEN, port->chars_in_buffer);
drivers/tty/vcc.c-398- if (!tosend)
--
drivers/tty/vcc.c-414-
drivers/tty/vcc.c:415: port->chars_in_buffer = 0;
drivers/tty/vcc.c-416- if (tty)
--
drivers/tty/vcc.c=817=static ssize_t vcc_write(struct tty_struct *tty, const u8 *buf, size_t count)
--
drivers/tty/vcc.c-839- tosend = min_t(size_t, count,
drivers/tty/vcc.c:840: (VCC_BUFF_LEN - port->chars_in_buffer));
drivers/tty/vcc.c-841-
--
drivers/tty/vcc.c-844-
drivers/tty/vcc.c:845: memcpy(&pkt->data[port->chars_in_buffer], &buf[total_sent],
drivers/tty/vcc.c-846- tosend);
drivers/tty/vcc.c:847: port->chars_in_buffer += tosend;
drivers/tty/vcc.c-848- pkt->tag.stype = tosend;
--
]
]
|
| 56/2 |
2026/05/18 03:09 |
llm |
expert |
0m
Model:
Tokens:
input: 55161
output: 46
thoughts: 404
Thoughts: **Analyzing a Potential Use-After-Free Vulnerability**
Okay, let's break this down. It looks like `tty_chars_in_buffer` is called within `kbd_keycode`. If the `tty` is a Virtual Terminal (`VT`), then `tty->ops` points to `con_ops`, and that specific `con_ops` implementation *doesn't* define `chars_in_buffer`. So, naturally, `tty_chars_in_buffer` should return zero, right? But hold on... `tty_chars_in_buffer` is *accessing* `tty->ops`. If the `tty` has been freed... that's a read from freed memory! The address in the report is `ffff888051204418`. Is that where `tty->ops` *should* be? Let me double-check the `tty_struct` layout.
In the standard, non-randomized layout, `ops` is at offset 256 bits, which is 32 bytes. But with `__randomize_layout` enabled, it could be anywhere! Now, the report indicates this:
```
BUG: KASAN: slab-use-after-free in __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:132 [inline]
BUG: KASAN: slab-use-after-free in _raw_spin_lock_irqsave+0x40/0x60 kernel/locking/spinlock.c:166
Read of size 1 at addr ffff888051204418 by task syz.6.4599/21087
```
A read of size 1. But `tty->ops` is a *pointer*. Reading a pointer would typically be a read of size 8 (on a 64-bit system, which seems likely here). So, how can we be reading only one byte when accessing `tty->ops`? And why is this happening inside `_raw_spin_lock_irqsave`? Time to investigate that function. I'll check its code path to trace the single byte read. This is definitely a use-after-free situation, and figuring out this discrepancy in read sizes is key to understanding the root cause.
|
| 57/2 |
2026/05/18 03:09 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/locking/spinlock.c IncludeLines:true Name:_raw_spin_lock_irqsave]
Results: map[SourceCode: 164: noinline unsigned long __lockfunc _raw_spin_lock_irqsave(raw_spinlock_t *lock)
165: {
166: return __raw_spin_lock_irqsave(lock);
167: }
SourceFile:kernel/locking/spinlock.c]
|
| 58/2 |
2026/05/18 03:09 |
llm |
expert |
0m
Model:
Tokens:
input: 56224
output: 51
thoughts: 16
Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience:
**Diving into `__raw_spin_lock_irqsave`**
Okay, time to dig into `__raw_spin_lock_irqsave`. I'm immediately interested in the core mechanics here. It's a low-level spinlock function, and the "irqsave" suffix implies it's intended to handle interrupt masking. That's the key: preventing race conditions with interrupt handlers when accessing shared resources. I need to understand how it's actually implemented to ensure atomicity, and understand the trade-offs of this approach. Are we saving the current interrupt state? Where is that stored? How does this interact with preemption? I want to see how this function guarantees that the critical section it protects is truly atomic, even in the face of potentially disruptive interrupts and context switches. Let's see how it achieves that.
|
| 59/2 |
2026/05/18 03:09 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:include/linux/spinlock_api_smp.h IncludeLines:true Name:__raw_spin_lock_irqsave]
Results: map[SourceCode: 125: static inline unsigned long __raw_spin_lock_irqsave(raw_spinlock_t *lock)
126: __acquires(lock) __no_context_analysis
127: {
128: unsigned long flags;
129:
130: local_irq_save(flags);
131: preempt_disable();
132: spin_acquire(&lock->dep_map, 0, 0, _RET_IP_);
133: LOCK_CONTENDED(lock, do_raw_spin_trylock, do_raw_spin_lock);
134: return flags;
135: }
SourceFile:include/linux/spinlock_api_smp.h]
|
| 60/2 |
2026/05/18 03:09 |
llm |
expert |
0m
Model:
Tokens:
input: 56703
output: 40
thoughts: 160
Thoughts: **Digging into the Lock Acquisition Process**
Okay, so I'm tracing through this code and I see `spin_acquire` ultimately calls `lock_acquire`. That's not unexpected, but I want to see the details of what's happening. Looking at the call stack, I see `lock_acquire` calls `__raw_spin_lock_irqsave`, which is an inline call that makes me think it's likely a relatively simple spinlock acquisition. I see that `__raw_spin_lock_irqsave` calls `_raw_spin_lock_irqsave` which is a good place to double-check against my understanding.
Ah, here's a key observation. `lock_acquire` is reading from `lock->dep_map`. That's got my attention. `dep_map` is a `struct lockdep_map`, which tells me this code is interacting with the lock dependency tracking mechanism. I need to refresh my memory on the specifics of how that works. I'll need to go to `kernel/locking/lockdep.c` and dig deeper into `lock_acquire` itself. I need to understand how the lock dependency information is being used during the acquisition process.
|
| 61/2 |
2026/05/18 03:10 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/locking/lockdep.c IncludeLines:true Name:lock_acquire]
Results: map[SourceCode:5821: /*
5822: * We are not always called with irqs disabled - do that here,
5823: * and also avoid lockdep recursion:
5824: */
5825: void lock_acquire(struct lockdep_map *lock, unsigned int subclass,
5826: int trylock, int read, int check,
5827: struct lockdep_map *nest_lock, unsigned long ip)
5828: {
5829: unsigned long flags;
5830:
5831: trace_lock_acquire(lock, subclass, trylock, read, check, nest_lock, ip);
5832:
5833: if (!debug_locks)
5834: return;
5835:
5836: /*
5837: * As KASAN instrumentation is disabled and lock_acquire() is usually
5838: * the first lockdep call when a task tries to acquire a lock, add
5839: * kasan_check_byte() here to check for use-after-free and other
5840: * memory errors.
5841: */
5842: kasan_check_byte(lock);
5843:
5844: if (unlikely(!lockdep_enabled())) {
5845: /* XXX allow trylock from NMI ?!? */
5846: if (lockdep_nmi() && !trylock) {
5847: struct held_lock hlock;
5848:
5849: hlock.acquire_ip = ip;
5850: hlock.instance = lock;
5851: hlock.nest_lock = nest_lock;
5852: hlock.irq_context = 2; // XXX
5853: hlock.trylock = trylock;
5854: hlock.read = read;
5855: hlock.check = check;
5856: hlock.hardirqs_off = true;
5857: hlock.references = 0;
5858:
5859: verify_lock_unused(lock, &hlock, subclass);
5860: }
5861: return;
5862: }
5863:
5864: raw_local_irq_save(flags);
5865: check_flags(flags);
5866:
5867: lockdep_recursion_inc();
5868: __lock_acquire(lock, subclass, trylock, read, check,
5869: irqs_disabled_flags(flags), nest_lock, ip, 0, 0, 0);
5870: lockdep_recursion_finish();
5871: raw_local_irq_restore(flags);
5872: }
SourceFile:kernel/locking/lockdep.c]
|
| 62/2 |
2026/05/18 03:10 |
llm |
expert |
0m
Model:
Tokens:
input: 57960
output: 40
thoughts: 400
Thoughts: **Decoding the KASAN Check in the Keyboard Driver**
Okay, here we go. My initial observation is that `kasan_check_byte(lock)` is explicitly targeting the *first* byte of the provided `lock`. The 1-byte read is coming directly from that function call. Now, the crucial piece is figuring out what `lock` represents in this context. It seems in `rt_mutex_slowunlock`, `lock` is actually `&lock->wait_lock`, which is interesting.
Hold on, I see something else. `rt_mutex_slowunlock` then calls `raw_spin_lock_irqsave(&lock->wait_lock, flags)`. So now I'm starting to put together the pieces. Earlier, `lock` in `lock_acquire` was `&lock->wait_lock.dep_map`, which gives me a new perspective on the variables here. I am reminded that `lock` in `rt_mutex_slowunlock` is a `struct rt_mutex_base *`, which is another very important thing to note. This means that `rt_mutex_slowunlock` is definitely receiving a pointer to a `struct rt_mutex_base`.
So where does this `rt_mutex_base` pointer originate? Ah, it's from `rt_spin_unlock(spinlock_t *lock)`. That function is called by `spin_unlock_irqrestore(spinlock_t *lock, unsigned long flags)`. This means that `kbd_keycode` calls `spin_unlock_irqrestore` on a `spinlock_t` that is *inside* a `tty_struct`! That's the link. So the problem is likely related to unlocking a spinlock within the `tty_struct` during keyboard input.
I need to nail down which specific `spinlock_t` is being unlocked in `kbd_keycode`. Let's re-examine that function. I see this snippet:
```c
1486: if (rep &&
1487: (!vc_kbd_mode(kbd, VC_REPEAT) ||
1488: (tty && !L_ECHO(tty) && tty_chars_in_buffer(tty)))) {
```
The `L_ECHO(tty)` check grabs my attention. I think that is where to focus. Let me dig into what that macro does.
|
| 63/2 |
2026/05/18 03:10 |
tool |
codesearch-definition-source |
0m
Error:
Args: map[ContextFile:include/linux/tty.h IncludeLines:true Name:L_ECHO]
Results: map[SourceCode: SourceFile:]
|
| 64/2 |
2026/05/18 03:10 |
llm |
expert |
0m
Model:
Tokens:
input: 58940
output: 20
thoughts: 11
Thoughts: Okay, here's my attempt at summarizing the thought process, as if it were my own, assuming the user is an expert.
**The Hunt for L_ECHO**
Alright, time to get down to it. Let's see... what's the most efficient way to pinpoint where `L_ECHO` is being used? Considering the potential scope of this project, I'm thinking the best starting point is a quick `grep`. I want to quickly search the codebase for the symbol `L_ECHO`. No need for anything fancy initially, just a plain `grep` to get a list of all occurrences. That'll give me a jumping off point to explore further and assess the impact. Simple, fast, and effective. Now, where to run it?
|
| 65/2 |
2026/05/18 03:10 |
tool |
grepper |
0m
Args: map[Expression:#define L_ECHO]
Results: map[Output:include/linux/tty.h-102-#define L_XCASE(tty) _L_FLAG((tty), XCASE)
include/linux/tty.h:103:#define L_ECHO(tty) _L_FLAG((tty), ECHO)
include/linux/tty.h:104:#define L_ECHOE(tty) _L_FLAG((tty), ECHOE)
include/linux/tty.h:105:#define L_ECHOK(tty) _L_FLAG((tty), ECHOK)
include/linux/tty.h:106:#define L_ECHONL(tty) _L_FLAG((tty), ECHONL)
include/linux/tty.h-107-#define L_NOFLSH(tty) _L_FLAG((tty), NOFLSH)
include/linux/tty.h-108-#define L_TOSTOP(tty) _L_FLAG((tty), TOSTOP)
include/linux/tty.h:109:#define L_ECHOCTL(tty) _L_FLAG((tty), ECHOCTL)
include/linux/tty.h:110:#define L_ECHOPRT(tty) _L_FLAG((tty), ECHOPRT)
include/linux/tty.h:111:#define L_ECHOKE(tty) _L_FLAG((tty), ECHOKE)
include/linux/tty.h-112-#define L_FLUSHO(tty) _L_FLAG((tty), FLUSHO)
]
|
| 66/2 |
2026/05/18 03:10 |
llm |
expert |
0m
Model:
Tokens:
input: 59511
output: 40
thoughts: 10
Thoughts: Okay, here's my interpretation of that thought process, tailored for an expert audience, and presented as if it were my own internal monologue:
**Checking a Critical Flag**
Alright, time to get to it. My initial thought is to immediately assess the status of `_L_FLAG`. I'm going to start with this, without delay. There is a strong chance that a key decision, or a critical process is dependent on this flag. It's the kind of variable that, if it's set incorrectly, can lead to cascading failures and a serious debugging headache. I'm going to determine its current state first because, whether it's correctly set or not, it will give me an immediate clue as to the next step.
|
| 67/2 |
2026/05/18 03:10 |
tool |
codesearch-definition-source |
0m
Error:
Args: map[ContextFile:include/linux/tty.h IncludeLines:true Name:_L_FLAG]
Results: map[SourceCode: SourceFile:]
|
| 68/2 |
2026/05/18 03:10 |
llm |
expert |
0m
Model:
Tokens:
input: 59737
output: 20
thoughts: 11
Thoughts: Okay, here's my take on those thoughts, tailored for an expert audience:
**Grep'ing for the Needle in the Haystack**
Right, let's get down to it. My initial instinct, when facing a situation like this, is to reach for `grep`. It's the workhorse, the reliable tool. The phrase "_L_FLAG" β that's the starting point. It's a specific string, likely a constant or variable name, something significant enough to warrant investigation. Now, depending on the scope of the search, I might refine that `grep` command. I'd be thinking about:
* **Contextual Clues:** Are we talking about C, C++, Python, JavaScript? That impacts the syntax I'd use, and any preliminary filtering needed. I'd add flags for context lines, perhaps `-C 5` or `-A 3 -B 3`, to see the surrounding code and understand how `_L_FLAG` is being used.
* **Case Sensitivity:** Is the casing critical? I'd immediately consider `-i` for a case-insensitive search if I'm not certain.
* **Recursive Search:** A simple `grep` might not cut it. The `-r` flag for recursive searches is almost a given if we're dealing with a project of any substantial size. I'd be mentally preparing for a potentially long output, or considering pipes to `less` or `head` or `tail` to manage the volume.
* **File Extension Filtering:** To optimize speed, if I have an idea about the files in which it is most likely to appear, I might restrict the search to only files matching a particular pattern, for example, `*.c`, `*.h`, or `*.js`.
* **Exclusion:** If I know where *not* to look, I'd incorporate `--exclude-dir` or `--exclude` into my `grep` command. Think `vendor` directories, `build` directories, or perhaps test code if that's not relevant at this point.
* **Beyond `grep`:** I'm mentally filing away the possibility that `grep` might not be the *best* tool. I might eventually switch to `ack` or `ag` (The Silver Searcher) for speed, or even consider a dedicated code search tool with better indexing if this grows into a complex investigation. But first, `grep`! Let's get that initial scan done.
|
| 69/2 |
2026/05/18 03:10 |
tool |
grepper |
0m
Args: map[Expression:#define _L_FLAG]
Results: map[Output:include/linux/tty.h-54-#define _C_FLAG(tty, f) ((tty)->termios.c_cflag & (f))
include/linux/tty.h:55:#define _L_FLAG(tty, f) ((tty)->termios.c_lflag & (f))
include/linux/tty.h-56-
]
|
| 70/2 |
2026/05/18 03:10 |
llm |
expert |
0m
Model:
Tokens:
input: 60392
output: 41
thoughts: 1348
Thoughts: **Analyzing a KASAN Slab-Use-After-Free in the TTY Subsystem**
Okay, so I'm digging into this KASAN report and trying to understand this use-after-free in the tty subsystem. It seems like `L_ECHO(tty)` doesn't involve any locks, which is good. But wait, what about `tty_chars_in_buffer(tty)`? I'm checking that function. No explicit locks there either, just a potential indirect call through `tty->ops->chars_in_buffer`. That's where things get interesting.
If `tty->ops->chars_in_buffer` isn't `NULL`, it could lead to trouble if `tty` is freed because then reading from `tty->ops` is reading from freed memory! However, if this happens, I expect the dereference of `tty->ops` to cause a crash. It appears the crash *isn't* directly on that read, but inside `__raw_spin_lock_irqsave`? This means that `tty->ops->chars_in_buffer` is a valid function pointer, but is calling `spin_lock_irqsave`.
So how could the `tty->ops` still be valid if `tty` is freed? KASAN's memory poisoning kicks in; the memory should be filled with `0xfb`. That would make `tty->ops` become `0xfbfbfbfbfbfbfbfb`, and that would cause a page fault on dereference. But, according to the memory dump, the memory *is* filled with `0xfb`.
Now I'm looking at the KASAN report more closely: It says "Read of size 1 at addr ffff888051204418". That address is *inside* the freed `tty_struct`! That's the key. That means the `lock` in `__raw_spin_lock_irqsave` is, in fact, `ffff888051204418`. Essentially, a `spin_lock_irqsave` or `spin_unlock_irqrestore` is happening on a lock that's *inside* the freed `tty_struct`!
So, which lock in `tty_struct` is the culprit? I have to review the offsets. We've got `atomic_write_lock`, `legacy_mutex`, `throttle_mutex`, `termios_rwsem`, `winsize_mutex`, `flow.lock`, `ctrl.lock`, and `files_lock` in `tty_struct`. I'm starting to suspect one of these.
Wait, the trace doesn't seem to be calling `spin_unlock_irqrestore`. The stack trace shows `rt_mutex_slowunlock`, which calls `rt_spin_unlock`. It *might* be possible that `kbd_keycode` calls `spin_unlock` on `flow.lock` or `ctrl.lock`! I need to investigate the code.
Checking `kbd_keycode` on line 1565 shows a function pointer dereference `(*k_handler[type])(vc, KVAL(keysym), !down);`. So, If `k_handler` is `k_fn`, it calls `guard(spinlock_irqsave)(&func_buf_lock);`. That's a global, so no. What about `k_unicode`? No, because that's called directly. If `k_handler` is `k_spec`...
|
| 71/2 |
2026/05/18 03:10 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/tty/vt/keyboard.c IncludeLines:true Name:k_spec]
Results: map[SourceCode: 645: /*
646: * Special key handlers
647: */
648: static void k_spec(struct vc_data *vc, unsigned char value, char up_flag)
649: {
650: if (up_flag)
651: return;
652: if (value >= ARRAY_SIZE(fn_handler))
653: return;
654: if ((kbd->kbdmode == VC_RAW ||
655: kbd->kbdmode == VC_MEDIUMRAW ||
656: kbd->kbdmode == VC_OFF) &&
657: value != KVAL(K_SAK))
658: return; /* SAK is allowed even in raw mode */
659: fn_handler[value](vc);
660: }
SourceFile:drivers/tty/vt/keyboard.c]
|
| 72/2 |
2026/05/18 03:10 |
llm |
expert |
0m
Model:
Tokens:
input: 62814
output: 41
thoughts: 9
Thoughts: Okay, here's my attempt at summarizing the thought process, tailored for an expert audience, and written in the first person:
**Analyzing the Function Handler**
Alright, time to dive into this. Let's start with `fn_handler`. I need to understand its role. What's it handling? Based on the context, I imagine this could be a top-level dispatcher, a specific module's interface, or maybe a utility function for a certain process. I'll need to carefully examine its signature and implementation. Are there any potential bottlenecks, or areas of potential inefficiency? Is it thread-safe? Does it handle errors gracefully? My immediate focus is going to be on identifying exactly what `fn_handler` does and what its implications are to the system. From there, I'll identify any possible vulnerabilities or inefficiencies.
|
| 73/2 |
2026/05/18 03:10 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/tty/vt/keyboard.c IncludeLines:true Name:fn_handler]
Results: map[SourceCode: 93: static fn_handler_fn *fn_handler[] = { FN_HANDLERS };
SourceFile:drivers/tty/vt/keyboard.c]
|
| 74/2 |
2026/05/18 03:10 |
llm |
expert |
0m
Model:
Tokens:
input: 63095
output: 21
thoughts: 11
Thoughts: Okay, here's my attempt at summarizing the thought process, tailored for an expert audience, and written in the first person:
**Navigating the Handler Landscape**
Right, let's dive into this. First things first, I need to take a look at `FN_HANDLERS`. Whenever I'm tackling a new system or debugging an existing one, I always start by mentally mapping out the available handlers. It's like having a mental flowchart of the crucial operations or functions. This is the cornerstone of understanding how requests are actually processed.
I suspect `FN_HANDLERS` likely holds the central registry or dispatch table for the application's core logic. I'll need to immediately figure out its structure: Is it a dictionary keyed by event type, a set of classes implementing a specific interface, or something more exotic?
Understanding its structure gives me a great mental map of the core logic. That will allow me to quickly trace back issues, or see opportunities for optimization. It will also help me be confident about adding functionality, and where I can make the most impact.
Let's start there.
|
| 75/2 |
2026/05/18 03:10 |
tool |
grepper |
0m
Args: map[Expression:#define FN_HANDLERS]
Results: map[Output:drivers/tty/vt/keyboard.c=82=static k_handler_fn *k_handler[16] = { K_HANDLERS };
drivers/tty/vt/keyboard.c-83-
drivers/tty/vt/keyboard.c:84:#define FN_HANDLERS\
drivers/tty/vt/keyboard.c-85- fn_null, fn_enter, fn_show_ptregs, fn_show_mem,\
]
|
| 76/2 |
2026/05/18 03:10 |
llm |
expert |
0m
Model:
Tokens:
input: 63482
output: 41
thoughts: 23
Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience:
**Diving into `FN_HANDLERS` in `keyboard.c`**
Okay, so I need to understand how function keys are handled within the virtual terminal driver. Time to dig into the `drivers/tty/vt/keyboard.c` file. Specifically, I'm thinking about the `FN_HANDLERS` structure. That's usually where the mapping between keycodes and actions resides, particularly for function key presses. I'm assuming it defines a table of handlers, likely function pointers, for different key combinations or states related to the function keys. I'll need to see how the kernel determines which handler to invoke based on the raw scancode input and possibly some state flags. Curious to see if they're using a simple lookup table or something more sophisticated like a state machine for handling modifiers or key sequences related to those function keys. I expect I'll find the logic for things like remapping or custom function key behaviors in there too. Let's see what the implementation actually looks like.
|
| 77/2 |
2026/05/18 03:11 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/tty/vt/keyboard.c IncludeLines:true Name:fn_null]
Results: map[SourceCode: 640: static void fn_null(struct vc_data *vc)
641: {
642: do_compute_shiftstate();
643: }
SourceFile:drivers/tty/vt/keyboard.c]
|
| 78/2 |
2026/05/18 03:11 |
llm |
expert |
0m
Model:
Tokens:
input: 63859
output: 21
thoughts: 15
Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience:
**Analyzing the `FN_HANDLERS` Macro**
Okay, let's dive right in and dissect that `FN_HANDLERS` macro. I need to see the complete definition, the whole picture. I'm going to want to examine how it's expanding, what preprocessor trickery it's employing, and what the overall structure looks like. Is it generating a dispatch table? Is it creating function pointers? What kind of data structures is it using internally? Does it handle argument passing directly, or does it abstract that away somehow? Are there any potential gotchas with scoping or name collisions that need to be considered? Understanding the macro's internal workings will allow me to quickly and accurately comprehend its operation and spot any potential vulnerabilities.
|
| 79/2 |
2026/05/18 03:11 |
tool |
grepper |
0m
Args: map[Expression:#define FN_HANDLERS]
Results: map[Output:drivers/tty/vt/keyboard.c=82=static k_handler_fn *k_handler[16] = { K_HANDLERS };
drivers/tty/vt/keyboard.c-83-
drivers/tty/vt/keyboard.c:84:#define FN_HANDLERS\
drivers/tty/vt/keyboard.c-85- fn_null, fn_enter, fn_show_ptregs, fn_show_mem,\
]
|
| 80/2 |
2026/05/18 03:11 |
llm |
expert |
0m
Model:
Tokens:
input: 64191
output: 22
thoughts: 24
Thoughts: Okay, let's dive into this. I'm going to focus on lines 84 through 90 of `drivers/tty/vt/keyboard.c`. I need to get a clear picture of what's happening within that specific segment of the code. I'm going to look at the surrounding context, and see how this little section fits into the bigger picture of the driver. I will be looking to pick out the important variables and functions that are used in this section. I want to understand the *why* as much as the *what*. What is this part of the keyboard driver *supposed* to be doing? What's its purpose within the overall architecture? Are there any potential areas for optimization, or perhaps bugs, that jump out? Specifically, I'm thinking about the way keypresses are handled and interpreted within the virtual terminal. Are there any edge cases that this code might be missing?
|
| 81/2 |
2026/05/18 03:11 |
tool |
grepper |
0m
Args: map[Expression:fn_null, fn_enter]
Results: map[Output:drivers/tty/vt/keyboard.c=82=static k_handler_fn *k_handler[16] = { K_HANDLERS };
--
drivers/tty/vt/keyboard.c-84-#define FN_HANDLERS\
drivers/tty/vt/keyboard.c:85: fn_null, fn_enter, fn_show_ptregs, fn_show_mem,\
drivers/tty/vt/keyboard.c-86- fn_show_state, fn_send_intr, fn_lastcons, fn_caps_toggle,\
]
|
| 82/2 |
2026/05/18 03:11 |
llm |
expert |
0m
Model:
Tokens:
input: 64580
output: 26
thoughts: 13
Thoughts: Okay, here's my interpretation of that request, formatted as requested:
**Analyzing the Excerpt: A Focused Examination**
Right, let's zero in. My initial approach to understanding this task is to pinpoint the exact section I need to analyze. The request specifies lines 84 to 92. Excellent. I'll need to read them with a critical eye, considering the context of the entire document, of course, but focusing my immediate attention on that specific segment. What does this snippet contribute to the larger argument or discussion? What are the key claims being made? Are there any logical leaps or unsupported assumptions? The objective is to understand the intent and impact of these specific lines within the broader framework. I'll need to keep an open mind, but remain skeptical, and evaluate the information carefully.
|
| 83/2 |
2026/05/18 03:11 |
tool |
grepper |
0m
Args: map[Expression:fn_show_state, fn_send_intr]
Results: map[Output:drivers/tty/vt/keyboard.c=82=static k_handler_fn *k_handler[16] = { K_HANDLERS };
--
drivers/tty/vt/keyboard.c-85- fn_null, fn_enter, fn_show_ptregs, fn_show_mem,\
drivers/tty/vt/keyboard.c:86: fn_show_state, fn_send_intr, fn_lastcons, fn_caps_toggle,\
drivers/tty/vt/keyboard.c-87- fn_num, fn_hold, fn_scroll_forw, fn_scroll_back,\
]
|
| 84/2 |
2026/05/18 03:11 |
llm |
expert |
0m
Model:
Tokens:
input: 64956
output: 22
thoughts: 13
Thoughts: Okay, here's my interpretation of that request, formatted as requested:
**Navigating the Text: A Targeted Focus**
Alright, the directive is clear. I need to zero in on lines 87 through 92 of this document. It seems we're not aiming for a general overview or synthesis of the entire work. Instead, this is a surgical approach. It suggests the author believes that the essence of whatever's being discussed, or some critical nuance, resides within that specific section. Perhaps it's a key argument, a pivotal piece of evidence, or a critical point where the author is making a shift. I will treat these lines as if they are the most important part of the entire document.
|
| 85/2 |
2026/05/18 03:11 |
tool |
grepper |
0m
Args: map[Expression:fn_num, fn_hold]
Results: map[Output:drivers/tty/vt/keyboard.c=82=static k_handler_fn *k_handler[16] = { K_HANDLERS };
--
drivers/tty/vt/keyboard.c-86- fn_show_state, fn_send_intr, fn_lastcons, fn_caps_toggle,\
drivers/tty/vt/keyboard.c:87: fn_num, fn_hold, fn_scroll_forw, fn_scroll_back,\
drivers/tty/vt/keyboard.c-88- fn_boot_it, fn_caps_on, fn_compose, fn_SAK,\
]
|
| 86/2 |
2026/05/18 03:11 |
llm |
expert |
0m
Model:
Tokens:
input: 65309
output: 26
thoughts: 13
Thoughts: Okay, here's my interpretation of reading lines 88 to 92, presented as a first-person summary, keeping in mind my expertise:
**Diving into the Specifics**
Alright, lines 88 to 92. Let's get down to the brass tacks, shall we? I need to understand the nuances embedded within this specific section of the text, and I need to assess its value in context. I'm going to carefully dissect these lines for any hidden assumptions, overlooked implications, or potential points of contention that I can use to improve the overall argument. My analytical eye is tuned to find relevant data points, and I'll see how they play out.
|
| 87/2 |
2026/05/18 03:11 |
tool |
grepper |
0m
Args: map[Expression:fn_boot_it, fn_caps_on]
Results: map[Output:drivers/tty/vt/keyboard.c=82=static k_handler_fn *k_handler[16] = { K_HANDLERS };
--
drivers/tty/vt/keyboard.c-87- fn_num, fn_hold, fn_scroll_forw, fn_scroll_back,\
drivers/tty/vt/keyboard.c:88: fn_boot_it, fn_caps_on, fn_compose, fn_SAK,\
drivers/tty/vt/keyboard.c-89- fn_dec_console, fn_inc_console, fn_spawn_con, fn_bare_num
]
|
| 88/2 |
2026/05/18 03:11 |
llm |
expert |
0m
Model:
Tokens:
input: 65661
output: 43
thoughts: 11
Thoughts: Okay, here's my attempt at summarizing that thought process, keeping in mind I'm speaking to a fellow expert:
**Investigating `fn_send_intr`**
Alright, time to dive in. My mind immediately goes to `fn_send_intr`. That's where the action is likely happening. We know this specific function is a key element in our workflow, and there may be a bug, so let's check it. Let's see what it's doing, how it's being called, and what its dependencies are. Let's get to work.
|
| 89/2 |
2026/05/18 03:11 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/tty/vt/keyboard.c IncludeLines:true Name:fn_send_intr]
Results: map[SourceCode: 588: static void fn_send_intr(struct vc_data *vc)
589: {
590: tty_insert_flip_char(&vc->port, 0, TTY_BREAK);
591: tty_flip_buffer_push(&vc->port);
592: }
SourceFile:drivers/tty/vt/keyboard.c]
|
| 90/2 |
2026/05/18 03:11 |
llm |
expert |
0m
Model:
Tokens:
input: 65956
output: 42
thoughts: 10
Thoughts: Okay, here's my attempt at summarizing the thought process, tailored for an expert audience, and written in the first person:
**Analyzing the Function `fn_SAK`**
Alright, let's dive in and dissect `fn_SAK`. I'm starting with this specific function because, based on the context, I suspect it's central to the current analysis or issue. I need to understand its role within the system, its inputs, its outputs, and, critically, how it's interacting with other components. My initial scan will focus on potential bottlenecks, areas for optimization, or points where errors might originate. I'll be looking for any signs of inefficient algorithms, memory leaks, or concurrency issues. The ultimate goal is to quickly assess its overall health and potential impact on the system's performance and stability. I'm already anticipating potential challenges, particularly if it interfaces with any external dependencies or handles complex data structures. Time to dig in and see what we're working with.
|
| 91/2 |
2026/05/18 03:11 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/tty/vt/keyboard.c IncludeLines:true Name:fn_SAK]
Results: map[SourceCode: 634: static void fn_SAK(struct vc_data *vc)
635: {
636: struct work_struct *SAK_work = &vc_cons[fg_console].SAK_work;
637: schedule_work(SAK_work);
638: }
SourceFile:drivers/tty/vt/keyboard.c]
|
| 92/2 |
2026/05/18 03:11 |
llm |
expert |
0m
Model:
Tokens:
input: 66332
output: 41
thoughts: 99
Thoughts: **Analyzing the Serial Driver Interrupt Handling**
Okay, let's break this down. My initial focus is on how data from the serial port is processed, specifically within the interrupt context. I see `fn_send_intr` is central to this. I immediately recognize `fn_send_intr` calls into `tty_insert_flip_char` and ultimately `tty_flip_buffer_push`. `tty_flip_buffer_push` then calls `tty_buffer_queue_work`. My immediate thought is, are we seeing contention here? I'm checking that we *shouldn't* see any explicit locking within the `tty_struct` itself inside these critical data paths.
It's looking like these calls are implemented without taking the `tty_struct` lock directly. That's good from a concurrency perspective. No immediate deadlocks should be apparent, and it looks like it's designed to minimize lock hold times.
I'm making a mental note to circle back to what `fn_hold` is doing in this equation. It's likely it might have implications for the data flow here. I'll need to check how it interfaces with the buffer pushing mechanism.
|
| 93/2 |
2026/05/18 03:11 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/tty/vt/keyboard.c IncludeLines:true Name:fn_hold]
Results: map[SourceCode: 510: static void fn_hold(struct vc_data *vc)
511: {
512: struct tty_struct *tty = vc->port.tty;
513:
514: if (rep || !tty)
515: return;
516:
517: /*
518: * Note: SCROLLOCK will be set (cleared) by stop_tty (start_tty);
519: * these routines are also activated by ^S/^Q.
520: * (And SCROLLOCK can also be set by the ioctl KDSKBLED.)
521: */
522: if (tty->flow.stopped)
523: start_tty(tty);
524: else
525: stop_tty(tty);
526: }
SourceFile:drivers/tty/vt/keyboard.c]
|
| 94/2 |
2026/05/18 03:11 |
llm |
expert |
0m
Model:
Tokens:
input: 66988
output: 41
thoughts: 49
Thoughts: Okay, here's my interpretation of that thought process, from an expert's perspective:
**Diving into TTY Flow Control**
Right, `fn_hold`. That's the one that deals with flow control, specifically accessing the `tty->flow.stopped` flag. And based on that flag's value, it's calling either `start_tty(tty)` or `stop_tty(tty)`. Okay, so that's the core logic. Now, I need to understand *how* it's doing that. Knowing the decision logic is just the starting point. I need to dig into the implementation details. Let me see what `start_tty` and `stop_tty` are actually doing. That's where the real magic (or potential bugs!) lies. I'll check those functions to see how they're affecting the hardware, the drivers, and the flow control signals themselves. I need to understand the side effects.
|
| 95/2 |
2026/05/18 03:12 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/tty/tty_io.c IncludeLines:true Name:start_tty]
Results: map[SourceCode: 780: /**
781: * start_tty - propagate flow control
782: * @tty: tty to start
783: *
784: * Start a tty that has been stopped if at all possible. If @tty was previously
785: * stopped and is now being started, the &tty_driver->start() method is invoked
786: * and the line discipline woken.
787: *
788: * Locking:
789: * flow.lock
790: */
791: void start_tty(struct tty_struct *tty)
792: {
793: guard(spinlock_irqsave)(&tty->flow.lock);
794: __start_tty(tty);
795: }
SourceFile:drivers/tty/tty_io.c]
|
| 96/2 |
2026/05/18 03:12 |
llm |
expert |
0m
Model:
Tokens:
input: 67533
output: 43
thoughts: 331
Thoughts: **UAF in TTY Flow Control on PREEMPT_RT!**
Okay, so *that's* interesting. I see that `start_tty` and `stop_tty` are both calling `guard(spinlock_irqsave)(&tty->flow.lock)`. That makes sense, keeping things threadsafe, and I know `tty->flow.lock` is nestled within the `tty_struct` structure. So, the obvious concern is, if the `tty` structure is freed β say, the TTY is released β and then either `start_tty` or `stop_tty` is called afterward, we're locking and unlocking memory that's no longer valid. The `guard` itself will manage the locking and unlocking, but when it goes out of scope it's going to call `spin_unlock_irqrestore(&tty->flow.lock, flags)`.
Now, here's where PREEMPT_RT comes into play. In that real-time context, `spin_unlock_irqrestore` itself calls `rt_spin_unlock`, which in turn leads to `rt_mutex_slowunlock`, which is the one that really caught my eye. Because it calls `raw_spin_lock_irqsave(&lock->wait_lock, flags)`. And remember, `lock` is effectively `&tty->flow.lock`. So, when `rt_mutex_slowunlock` is called, it's accessing `&tty->flow.lock.wait_lock`! Even better, I know that `lock_acquire` subsequently calls `kasan_check_byte(&lock->wait_lock)`.
That's it! That perfectly lines up with the stack trace and the UAF read of size 1 that's reported. This is the smoking gun! So, the bug is being triggered by the "Hold" key (Scroll Lock) on the keyboard when the TTY is freed.
Now, I'm just curious, how exactly is the TTY being freed while `vc->port.tty` still points to it? Time to investigate `tty_release_struct`.
|
| 97/2 |
2026/05/18 03:12 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/tty/tty_io.c IncludeLines:true Name:tty_release_struct]
Results: map[SourceCode:1668: /**
1669: * tty_release_struct - release a tty struct
1670: * @tty: tty device
1671: * @idx: index of the tty
1672: *
1673: * Performs the final steps to release and free a tty device. It is roughly the
1674: * reverse of tty_init_dev().
1675: */
1676: void tty_release_struct(struct tty_struct *tty, int idx)
1677: {
1678: /*
1679: * Ask the line discipline code to release its structures
1680: */
1681: tty_ldisc_release(tty);
1682:
1683: /* Wait for pending work before tty destruction commmences */
1684: tty_flush_works(tty);
1685:
1686: tty_debug_hangup(tty, "freeing structure\n");
1687: /*
1688: * The release_tty function takes care of the details of clearing
1689: * the slots and preserving the termios structure.
1690: */
1691: mutex_lock(&tty_mutex);
1692: release_tty(tty, idx);
1693: mutex_unlock(&tty_mutex);
1694: }
SourceFile:drivers/tty/tty_io.c]
|
| 98/2 |
2026/05/18 03:12 |
llm |
expert |
0m
Model:
Tokens:
input: 68768
output: 41
thoughts: 87
Thoughts: Here's my thought process, as it stands:
**Debugging the TTY Release Process**
Okay, so I'm tracing the execution of `release_tty` and things aren't quite adding up. My initial thought is that `release_tty` invokes `tty->driver->ops->remove(tty->driver, tty)`. Fair enough. But, I'm working with a virtual terminal, a VT. And, if I recall correctly, the `con_ops` structure, associated with the console device, doesn't actually implement a `remove` operation. That's a potential issue. It raises the question of what happens when that non-existent `remove` is called.
Then I quickly remember there is another function called by the same process, `tty_kref_put(tty)`. I need to remember that too, so I'll keep that in mind.
Now the million-dollar question: when does the virtual console's port tty ( `vc->port.tty` ) get set to `NULL`? I need to figure out the exact point at which that connection is severed. The obvious candidate for that seems to be `con_close`. That's where I need to focus my investigation. I'll check what that function does to understand when the `tty` pointer is invalidated.
|
| 99/2 |
2026/05/18 03:12 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/tty/vt/vt.c IncludeLines:true Name:con_close]
Results: map[SourceCode:3780: static void con_close(struct tty_struct *tty, struct file *filp)
3781: {
3782: /* Nothing to do - we defer to shutdown */
3783: }
SourceFile:drivers/tty/vt/vt.c]
|
| 100/2 |
2026/05/18 03:12 |
llm |
expert |
0m
Model:
Tokens:
input: 69270
output: 41
thoughts: 9
Thoughts: Okay, here's my interpretation of that thought process, tailored for an expert audience, and written in the first person:
**Analyzing the `con_shutdown` Variable**
Alright, time to dig in. The immediate thought here is, "Let's check `con_shutdown`." This suggests I'm likely dealing with some form of concurrent or distributed system, perhaps related to network connections or inter-process communication, where graceful shutdown is a critical concern. `con_shutdown` likely represents a flag, variable, or data structure used to signal the need to initiate a controlled shutdown sequence within that environment. I'm probably looking to understand its current state, how it's being set, what conditions trigger it, and how the various components respond to its signal. I'm already mentally running through the possible implications: race conditions, deadlocks, resource leaks if shutdown isn't handled correctly. I'll need to assess the level of thread safety, potential for false positives, and whether the shutdown logic is robust enough to handle unexpected errors or external interruptions. The exact context, the language used, and any associated logging will be vital to making a solid diagnosis and moving forward. I'm anticipating that this is a key variable in determining the stability and reliability of the whole system.
|
| 101/2 |
2026/05/18 03:12 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/tty/vt/vt.c IncludeLines:true Name:con_shutdown]
Results: map[SourceCode:3785: static void con_shutdown(struct tty_struct *tty)
3786: {
3787: struct vc_data *vc = tty->driver_data;
3788: BUG_ON(vc == NULL);
3789:
3790: guard(console_lock)();
3791: vc->port.tty = NULL;
3792: }
SourceFile:drivers/tty/vt/vt.c]
|
| 102/2 |
2026/05/18 03:12 |
llm |
expert |
0m
Model:
Tokens:
input: 69726
output: 41
thoughts: 45
Thoughts: Okay, here's my take on those thoughts, framed as my own:
**Connecting the Dots in the TTY Lifecycle**
Hmm, so `con_shutdown` is the key to nullifying the `vc->port.tty` pointer. That makes sense, in terms of cleanup. But the immediate question that pops up is where `con_shutdown` is called from. The text says it's from `tty_release_struct`. Alright, so `tty_release_struct` is the call site to focus on, and that is where the important work occurs. I need to understand that. Let's delve into the logic of `release_tty` to see how everything is orchestrated. It's time to see how all the pieces fit together during the deallocation process.
|
| 103/2 |
2026/05/18 03:12 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/tty/tty_io.c IncludeLines:true Name:release_tty]
Results: map[SourceCode:1561: /**
1562: * release_tty - release tty structure memory
1563: * @tty: tty device release
1564: * @idx: index of the tty device release
1565: *
1566: * Release both @tty and a possible linked partner (think pty pair),
1567: * and decrement the refcount of the backing module.
1568: *
1569: * Locking:
1570: * tty_mutex
1571: * takes the file list lock internally when working on the list of ttys
1572: * that the driver keeps.
1573: */
1574: static void release_tty(struct tty_struct *tty, int idx)
1575: {
1576: /* This should always be true but check for the moment */
1577: WARN_ON(tty->index != idx);
1578: WARN_ON(!mutex_is_locked(&tty_mutex));
1579: if (tty->ops->shutdown)
1580: tty->ops->shutdown(tty);
1581: tty_save_termios(tty);
1582: tty_driver_remove_tty(tty->driver, tty);
1583: if (tty->port)
1584: tty->port->itty = NULL;
1585: if (tty->link)
1586: tty->link->port->itty = NULL;
1587: if (tty->port)
1588: tty_buffer_cancel_work(tty->port);
1589: if (tty->link)
1590: tty_buffer_cancel_work(tty->link->port);
1591:
1592: tty_kref_put(tty->link);
1593: tty_kref_put(tty);
1594: }
SourceFile:drivers/tty/tty_io.c]
|
| 104/2 |
2026/05/18 03:12 |
llm |
expert |
0m
Model:
Tokens:
input: 70521
output: 42
thoughts: 1547
Thoughts: **Use-After-Free Vulnerability in Virtual Console TTY Release**
Okay, so here's what I've got. It seems like we have a nasty Use-After-Free (UAF) bug lurking in the virtual console code, specifically around how TTY structures are released in conjunction with keyboard event handling.
First, `release_tty` is called. It calls `tty->ops->shutdown(tty)` and then crucially sets `vc->port.tty = NULL` and decrements the TTY's kref. The problem comes down to `kbd_keycode` accessing the TTY after this nulling out. The `vc->port.tty` is read into a local variable, `tty`, in `kbd_keycode`. If this read happens BEFORE `con_shutdown` sets `vc->port.tty = NULL`, but then the TTY is freed by `release_tty` BEFORE it is used, we have a problem.
`kbd_keycode` gets called from `kbd_event`. Now, `kbd_event` takes the `kbd_event_lock`. The lock itself protects against preemption within the same CPU. However, `con_shutdown` does *not* hold this lock, and so it can run concurrently. So, if `kbd_keycode` reads the TTY pointer, `con_shutdown` NULLs it out, `release_tty` frees it, and then `kbd_keycode` calls `fn_hold`, the bug is triggered.
The core of the issue is in `fn_hold`, which is called from `kbd_keycode`. `fn_hold` reads `vc->port.tty`, but it doesn't appear to re-read it after the initial call to `kbd_keycode`, so a race is possible if `con_shutdown` runs in between the two reads!
`kbd_event` is called with interrupts *disabled*, which means the CPU will not be preempted, but another CPU could be running concurrently! Let's say CPU 0 is running `kbd_event`, and CPU 1 is running `tty_release_struct`, which leads to `release_tty` and eventually `con_shutdown`. In this scenario, CPU 0 reads `vc->port.tty` (which is not NULL). Meanwhile, CPU 1 sets `vc->port.tty = NULL` and frees the TTY structure. Then, on CPU 0, `fn_hold` accesses the already-freed `tty` pointer. Since `kbd_event` disables interrupts, it can't be preempted. This allows a scenario where the TTY structure is used *after* it has been freed. This creates a data race: `kbd_event` doesn't synchronize with `tty_release_struct`.
Specifically, `fn_hold` might access `tty->flow.stopped` after the TTY has been freed. Crucially, `fn_hold` calls `start_tty` or `stop_tty` which calls `__start_tty`. And in `__start_tty` it accesses `tty->flow.stopped`, and potentially `tty->ops->start(tty)`. This is where it gets bad.
In `__start_tty`, we have this flow:
1. Lock `tty->flow.lock` (a spinlock in the freed memory).
2. Read `tty->flow.stopped`, `tty->flow.tco_stopped`.
3. Write `tty->flow.stopped = false`.
4. Read `tty->ops`.
5. Call `tty->ops->start(tty)`.
If the TTY structure has been freed, any of these accesses could lead to a crash. But the real vulnerability is the call to `tty->ops->start(tty)`.
If an attacker can control the contents of the freed `tty_struct`, they can control `tty->ops`. This means an attacker can control the function pointer `tty->ops->start` and redirect execution to an attacker-controlled address. This leads to a textbook control-flow hijack.
So, yeah, it looks like this is EXPLOITABLE. A classic Use-After-Free, but with a potential for full control-flow hijacking. We need to look into this more deeply.
|
| 105/2 |
2026/05/18 03:12 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/tty/tty_io.c IncludeLines:true Name:__start_tty]
Results: map[SourceCode: 770: void __start_tty(struct tty_struct *tty)
771: {
772: if (!tty->flow.stopped || tty->flow.tco_stopped)
773: return;
774: tty->flow.stopped = false;
775: if (tty->ops->start)
776: tty->ops->start(tty);
777: tty_wakeup(tty);
778: }
SourceFile:drivers/tty/tty_io.c]
|
| 106/2 |
2026/05/18 03:12 |
llm |
expert |
0m
Model:
Tokens:
input: 73183
output: 44
thoughts: 2598
Thoughts: **My Analysis of a Potential Privilege Escalation Vulnerability**
Okay, so here's what I've got. The core issue is a Use-After-Free (UAF) vulnerability within the TTY subsystem, specifically in the `kbd_keycode` function. It seems that `tty->ops->start(tty)` can be exploited, which is concerning. The attacker can control this function pointer and gain code execution by spraying the `kmalloc-cg-2k` object with a fake `tty_struct` where `tty->ops` points to something malicious like a ROP gadget or even `system`. The fact that `tty` is the first argument (`rdi`) means I can fully control the execution. This is a big deal for local privilege escalation!
Now, how can this be triggered without special privileges? After some thought, I've determined that the bug requires a freed TTY and a concurrent keyboard event that calls `fn_hold`, the most convenient example of which would be the Scroll Lock key. Unprivileged users can open and close PTYs or VTs, but VTs might be easier. The foreground console `/dev/tty` might be accessible, and the key press is handled by the input subsystem.
My first thought was that unprivileged processes can't inject keyboard events. While normally `/dev/input/eventX` is root-only, anyone at the physical console *can* press Scroll Lock, making this a "Peripheral Trigger" scenario. This makes it possible from an unprivileged user with physical access.
PTYs are not vulnerable because `kbd_keycode` is specific to the VT keyboard driver. No remote triggering through network.
Can unprivileged processes do this? No, not normally. However, I can open and close `/dev/tty` (if it's a VT) and press the key. Closing the TTY requires the `tty_release_struct` function to be called, which happens when the last reference to the TTY is dropped. If I log in on a VT, my shell holds a reference to the VT's TTY.
I can't just close the VT myself because I need the background process. I need to be able to open `/dev/tty1`, fork a background process that keeps it open, then logout and have that background process close it. I think I can do that. I can then press Scroll Lock to trigger the vulnerability!
So, the answer to the prompt questions:
* Exploitable: Yes
* Denial of Service: Yes
* Accessible From Unprivileged Processes: Yes (open/close `/dev/tty` and press a key)
* Accessible From User Namespaces: Yes (it is reachable). Although userns processes don't have access to devices, this doesn't matter because it can be done from unprivileged, so it's a subset.
Regarding user namespaces and input events, even with all capabilities, it's not possible to create input device nodes. But this doesn't matter because the bug is triggered by the physical keyboard, which the user can press.
And what about a KVM Guest? A guest has a virtual keyboard, so they can use the VMM console to press Scroll Lock via VNC or SPICE. So, yes, it can be triggered in a KVM Guest!
Regarding VM Host Trigger in a Confidential Computing context, the Host controls the emulated keyboard and can inject arbitrary keystrokes, and trigger it that way. The host *can* force the `tty_struct` to be freed, though it's not super straightforward. The Host *can* reliably inject the keyboard interrupt, making this possible.
No on the Ethernet Network Trigger and Other Remote Trigger. And no on the Malicious Filesystem Trigger.
Also, it turns out that there is another control-flow hijack. If the attacker can control the contents of any TTY, even without pressing Scroll Lock. I can do this by holding down a key while a VT is closing. Then `tty_chars_in_buffer` will trigger the vulnerability. I don't even need Scroll Lock.
So, here's the race:
1. `kbd_keycode` reads `vc->port.tty` (not NULL).
2. `con_shutdown` sets `vc->port.tty = NULL`.
3. `release_tty` frees the `tty`.
4. `kbd_keycode` accesses `tty->termios.c_lflag` and `tty->ops`.
If `tty` is NULL, then it will bypass the vulnerability. The real problem is checking `kbd_keycode` preemption with `atomic_notifier_call_chain` calling external notifiers. It may cause problems. I must verify if `tty_struct` is freed by RCU. I will investigate `tty_kref
|
| 107/2 |
2026/05/18 03:13 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/tty/tty_io.c IncludeLines:true Name:tty_kref_put]
Results: map[SourceCode:1547: /**
1548: * tty_kref_put - release a tty kref
1549: * @tty: tty device
1550: *
1551: * Release a reference to the @tty device and if need be let the kref layer
1552: * destruct the object for us.
1553: */
1554: void tty_kref_put(struct tty_struct *tty)
1555: {
1556: if (tty)
1557: kref_put(&tty->kref, queue_release_one_tty);
1558: }
SourceFile:drivers/tty/tty_io.c]
|
| 108/2 |
2026/05/18 03:13 |
llm |
expert |
0m
Model:
Tokens:
input: 77057
output: 45
thoughts: 26
Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience:
**Analyzing `queue_release_one_tty`**
Okay, so we're looking at `queue_release_one_tty`. I immediately recognize the function name, it suggests a core interaction with the tty subsystem, specifically the release of a resource, likely a queue or similar structure associated with a particular tty device. My immediate thought is to delve into the implementation to understand the locking semantics involved, the context in which it's called, and what resources are actually being managed. Iβm thinking we'll probably see some interaction with a wait queue, maybe condition variables, and definitely some synchronization primitives like mutexes or spinlocks to ensure thread-safety. I want to see how this function integrates with the higher-level tty driver framework, and what the potential for race conditions or deadlocks might be, given it handles releasing resources that other parts of the system are probably waiting on. Let's see what the code reveals!
|
| 109/2 |
2026/05/18 03:13 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/tty/tty_io.c IncludeLines:true Name:queue_release_one_tty]
Results: map[SourceCode:1536: static void queue_release_one_tty(struct kref *kref)
1537: {
1538: struct tty_struct *tty = container_of(kref, struct tty_struct, kref);
1539:
1540: /* The hangup queue is now free so we can reuse it rather than
1541: * waste a chunk of memory for each port.
1542: */
1543: INIT_WORK(&tty->hangup_work, release_one_tty);
1544: schedule_work(&tty->hangup_work);
1545: }
SourceFile:drivers/tty/tty_io.c]
|
| 110/2 |
2026/05/18 03:13 |
llm |
expert |
0m
Model:
Tokens:
input: 77542
output: 43
thoughts: 40
Thoughts: Okay, let's see. My first thought is: **Hang on a second! I need to clarify something about how `tty_struct` is managed in the kernel.** I thought it was freed immediately, but that doesn't seem to be the case. Now I remember... it's actually freed asynchronously, using a workqueue. Okay, so `release_one_tty` is the key function. I need to take a closer look at that function to fully understand the release process and how it handles potential race conditions or resource cleanup. Let me examine `release_one_tty` more closely.
|
| 111/2 |
2026/05/18 03:13 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:drivers/tty/tty_io.c IncludeLines:true Name:release_one_tty]
Results: map[SourceCode:1499: /**
1500: * release_one_tty - release tty structure memory
1501: * @work: work of tty we are obliterating
1502: *
1503: * Releases memory associated with a tty structure, and clears out the
1504: * driver table slots. This function is called when a device is no longer
1505: * in use. It also gets called when setup of a device fails.
1506: *
1507: * Locking:
1508: * takes the file list lock internally when working on the list of ttys
1509: * that the driver keeps.
1510: *
1511: * This method gets called from a work queue so that the driver private
1512: * cleanup ops can sleep (needed for USB at least)
1513: */
1514: static void release_one_tty(struct work_struct *work)
1515: {
1516: struct tty_struct *tty =
1517: container_of(work, struct tty_struct, hangup_work);
1518: struct tty_driver *driver = tty->driver;
1519: struct module *owner = driver->owner;
1520:
1521: if (tty->ops->cleanup)
1522: tty->ops->cleanup(tty);
1523:
1524: tty_driver_kref_put(driver);
1525: module_put(owner);
1526:
1527: spin_lock(&tty->files_lock);
1528: list_del_init(&tty->tty_files);
1529: spin_unlock(&tty->files_lock);
1530:
1531: put_pid(tty->ctrl.pgrp);
1532: put_pid(tty->ctrl.session);
1533: free_tty_struct(tty);
1534: }
SourceFile:drivers/tty/tty_io.c]
|
| 112/2 |
2026/05/18 03:13 |
llm |
expert |
0m
Model:
Tokens:
input: 78318
output: 43
thoughts: 5292
Thoughts: **Analyzing a Virtual Terminal User-After-Free Vulnerability in a PREEMPT_RT Kernel**
Okay, so I'm digging into this UAF issue within the Linux kernel, specifically related to virtual terminals (`tty_struct`) and the `kbd_keycode` function. The core of the problem seems to be a race condition that's *much* worse under a PREEMPT_RT kernel.
I see that `tty_struct` is freed in a workqueue. This alone is a huge red flag because it means there's a significant time window where a race could happen. The process unfolds as follows: On CPU 0, `kbd_keycode` might read `vc->port.tty`. Concurrently, CPU 1 calls `tty_release_struct`, which leads to a call to `release_tty` and then `con_shutdown`, setting `vc->port.tty` to `NULL`. CPU 1 then schedules `release_one_tty` through `tty_kref_put`. Eventually, CPU 2 runs `release_one_tty`, which frees the `tty_struct`. Now, if CPU 0 is still in `kbd_keycode` at this point, accessing `tty->termios.c_lflag` or `tty->flow.stopped` results in a UAF.
Normally, the time window for this race should be small because `kbd_keycode` is generally fast. However, I realize `release_one_tty` is a workqueue item and can run on any CPU. So CPU 2 can indeed free the `tty_struct` *while* CPU 0 is inside `kbd_keycode`.
Then I realize it *cannot* be preempted on a standard kernel because of interrupts being disabled. However, this changes with PREEMPT_RT, because `kbd_event` is called with interrupts disabled.
In PREEMPT_RT, because `spin_lock_irqsave` *does not* actually disable interrupts, but only disables migration and acquires a mutex, the function is *fully* preemptible! This creates an *infinite* race window!
Here's where it gets interesting. `kbd_keycode` calls `atomic_notifier_call_chain`, which could be time-consuming. However, more likely, this race is hit during heavy fuzzing by syzkaller.
Let's dissect the exploit. An attacker can trigger the UAF by opening and closing `/dev/tty` while injecting keyboard events, and can read/write the freed `tty_struct` after the bug triggers. The call to `tty_chars_in_buffer(tty)` calls `tty->ops->chars_in_buffer(tty)` which is a function pointer call from the freed memory! It seems that spraying `kmalloc-cg-2k` with fake `tty_struct` objects and hijacking the control flow by controlling `tty->ops` to execute code with kernel privileges is possible.
I also wonder if `tty_chars_in_buffer` is the only UAF. The KASAN report and address offsets suggests the UAF can result on `tty->flow.lock` within `tty_struct`, which is protected by a spinlock. But in PREEMPT_RT, this spinlock is an `rt_mutex`.
And the stack trace makes me see that `kbd_event_lock` *is* unlocked, and because it is a global, the problem must be within `tty_struct`. Why doesn't the KASAN catch a read of `tty->flow.stopped`? Then I get it. Because `tty->flow.stopped` is only 1 byte in size, KASAN can miss it, but the lock is a larger region. This is why the UAF is caught within `__raw_spin_lock_irqsave`, because it's accessing this lock, but this code is called by `guard(spinlock_irqsave)` which calls `spin_lock_irqsave`, and that explains the vulnerability!
|
| 113/2 |
2026/05/18 03:14 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:kernel/locking/spinlock_rt.c IncludeLines:true Name:rt_spin_lock]
Results: map[SourceCode: 54: void __sched rt_spin_lock(spinlock_t *lock) __acquires(RCU)
55: {
56: spin_acquire(&lock->dep_map, 0, 0, _RET_IP_);
57: __rt_spin_lock(lock);
58: }
SourceFile:kernel/locking/spinlock_rt.c]
|
| 114/2 |
2026/05/18 03:14 |
llm |
expert |
0m
Model:
Tokens:
input: 84620
output: 66
thoughts: 1538
Thoughts: **A Deep Dive into a Nasty UAF Bug**
Okay, let's break this down. My initial thought was that the issue was in `rt_spin_lock`, but it turns out that's not the case. The crucial thing to understand is the KASAN report and the stack trace. The UAF is being triggered in `rt_mutex_slowunlock`, but it's happening during the *unlock* operation. This is key!
The KASAN report is happening when `kasan_check_byte` is called on `&lock->dep_map`, which happens inside `lock_acquire`, which is called within `spin_acquire`. The stack trace clearly shows the path: `lock_acquire` -> `__raw_spin_lock_irqsave` -> `rt_mutex_slowunlock`. So, the problem is not in the initial lock but in the unlock. This means the object was freed *after* it was locked, but *before* it was unlocked.
Initially, I looked at `kbd_event_lock`, but that's a global variable and thus never freed. Then, I considered the possibility of a lock associated with a `tty_struct` β specifically, `tty->flow.lock`. Aha! `start_tty` locks and unlocks `tty->flow.lock` within the same function.
The race condition clicked. CPU 0 calls `start_tty`, which locks `tty->flow.lock`. Then, CPU 1 calls `release_one_tty` and frees the `tty_struct` while CPU 0 is still holding `tty->flow.lock`. `release_one_tty` doesn't acquire `tty->flow.lock` before freeing the structure. Then, back in CPU 0, `start_tty` finishes and unlocks `tty->flow.lock`, triggering the UAF.
This confirms the issue is within `fn_hold` or some function like it. It's a classic missing reference count bug: `kbd_keycode` gets `tty = vc->port.tty` but doesn't take a reference (like `tty_kref_get`). Thus, the `tty` object can be freed concurrently.
This is exploitable! The attacker just needs to spray a new object at the freed memory location. Since `__start_tty` reads `tty->ops->start`, if the attacker sprays the memory *before* CPU 0 reads it, CPU 0 will jump to the attacker's payload. The attacker, via CPU 1, could free the `tty_struct`, reallocate the memory, and overwrite the `tty->ops` to point to malicious code. The subsequent read and execution by CPU 0 becomes a perfect control-flow hijack.
The bug is exploitable, unprivileged, user-namespace-compatible, VM-guest-triggerable, and VM-host-triggerable. The peripheral trigger is confirmed.
|
| 115/2 |
2026/05/18 03:14 |
tool |
set-results |
0m
Args: map[DenialOfService:true Exploitable:true FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:true RemoteTrigger:false Unprivileged:true UserNamespace:true VMGuestTrigger:true VMHostTrigger:true]
Results: map[DenialOfService:true Exploitable:true FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:true RemoteTrigger:false Unprivileged:true UserNamespace:true VMGuestTrigger:true VMHostTrigger:true]
|
| 116/2 |
2026/05/18 03:14 |
llm |
expert |
0m
Model:
Tokens:
input: 86909
output: 757
thoughts: 473
Thoughts: **Final Assessment & Response Formulation**
Okay, the dust has settled, the analysis is complete, and I've got a clear picture of what's going on. This is a classic Use-After-Free (UAF) bug, and it's located right in the heart of the VT keyboard driver, specifically in `drivers/tty/vt/keyboard.c`. It looks like the issue stems from `kbd_keycode` and its subordinate functions, like `fn_hold`, accessing the foreground console's TTY structure (`vc->port.tty`) without the proper safeguards. There's no reference count (`tty_kref_get`) taken, and crucially, no lock held to prevent the TTY from being released.
The race condition is the key here. While `fn_hold` is happily processing keyboard events, `tty_release_struct` could be called if all file descriptors to the VT are closed. This eventually calls `release_one_tty`, which is responsible for freeing the `tty_struct`. If the TTY is freed *while* `fn_hold` is still executing β let's say, while holding `tty->flow.lock` β we have a UAF. The provided crash report hits this exact issue, with the UAF detected when `start_tty` tries to unlock the `tty->flow.lock` after the memory has been reallocated.
The exploitability is, frankly, concerning. Inside `__start_tty`, which is called by `fn_hold`, the code reads `tty->ops->start` and calls it. If an attacker can control what that `tty->ops` pointer points to β which, given a freed object in a `kmalloc-cg-2k` cache, is entirely plausible β they can overwrite it with a pointer to a fake `tty_operations` structure. Thatβs a direct path to kernel privilege escalation. Itβs essentially arbitrary code execution.
The trigger vectors are also worrying:
* **Unprivileged access**: A local user, even without elevated privileges, can trigger this simply by opening and closing `/dev/tty` and then hitting Scroll Lock, or holding down a key to generate repeat events. That's a huge attack surface.
* **Peripheral injection**: A compromised USB keyboard could inject these keystrokes. Not ideal, but the implications are clear: the bug's accessibility is far reaching.
* **Virtual machines**: Both a VM guest and a host can trigger this. The ability for a host to inject keystrokes into a confidential guest is extremely concerning. This is not just a local privilege escalation; it's a cross-VM escape.
Now, I'm ready to craft the final response. It's going to emphasize the severity, the broad applicability, and the need for immediate mitigation.
|
| 117/1 |
2026/05/18 03:15 |
action |
format-explanation |
0m
Results: map[Explanation:Based on the analysis of the bug report and the kernel source code, here is the
assessment of the vulnerability:
### Root Cause Analysis
The bug is a Use-After-Free (UAF) in the Virtual Terminal (VT) keyboard driver
(`drivers/tty/vt/keyboard.c`).
When processing keyboard events, `kbd_keycode()` retrieves the foreground
console's TTY via `vc->port.tty` and passes it to various handlers (like
`fn_hold()` when the Scroll Lock key is pressed, or `tty_chars_in_buffer()` for
repeating keys). However, it does so without taking a reference count
(`tty_kref_get()`) or holding a lock that would prevent the TTY from being
concurrently destroyed.
If an unprivileged user closes all file descriptors associated with the VT,
`tty_release_struct()` is invoked, which eventually schedules
`release_one_tty()` in a workqueue to free the `tty_struct`. If the `tty_struct`
is freed while the keyboard handler is still using it (e.g., while holding
`tty->flow.lock` inside `start_tty()`), a UAF occurs. The KASAN report
specifically catches the UAF during the spinlock unlock path
(`rt_mutex_slowunlock` -> `raw_spin_lock_irqsave`) because the underlying memory
backing the lock was freed while the lock was held.
### Security Impact
* **Exploitable:** **Yes**. This UAF is highly exploitable for local privilege
escalation (LPE). While the `tty_struct` is freed, functions like
`__start_tty()` or `tty_chars_in_buffer()` dereference the `tty->ops` pointer
and perform indirect function calls (e.g., `tty->ops->start(tty)`). An attacker
can spray the `kmalloc-cg-2k` slab cache to reallocate the freed `tty_struct`
with attacker-controlled data, pointing `tty->ops` to a fake `tty_operations`
table. This allows for a direct control-flow hijack to execute arbitrary code
(e.g., a ROP chain) in the kernel context.
* **Denial Of Service:** **Yes**. If not successfully exploited for LPE, the
wild pointers and memory corruption will reliably crash the kernel.
* **Accessible From Unprivileged Processes:** **Yes**. A typical local
unprivileged user logged into a VT can open/close `/dev/tty` to trigger the
allocation and freeing of the `tty_struct`, while concurrently pressing keys
(like Scroll Lock) to hit the race condition.
* **Accessible From User Namespaces:** **Yes**. The bug doesn't strictly require
user namespaces, but a process within a user namespace that has access to a VT
can trigger it just the same.
* **Peripheral Trigger:** **Yes**. A malicious USB device acting as a keyboard
can precisely inject the necessary keystrokes (like Scroll Lock or rapid
repeating keys) to win the race condition against the TTY teardown.
* **VM Guest Trigger:** **Yes**. A user inside a KVM guest can trigger this
using the emulated virtual keyboard.
* **VM Host Trigger in The Confidential Computing Context:** **Yes**. A
malicious hypervisor can inject arbitrary keystrokes via the
paravirtualized/emulated keyboard device into a confidential guest to trigger
the UAF and hijack the guest kernel's control flow.
* **Network / Remote / Filesystem Trigger:** **No**. The bug is tied to the
local VT keyboard input subsystem and cannot be triggered via network packets or
filesystem parsing.]
|