| 0/0 |
2026/06/30 00:01 |
flow |
assessment-security |
53m
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:
**Bug Mechanism:**
The bug is a Denial of Service (DoS) caused by a long timeout while holding a
global mutex (`nfsd_mutex`).
When a user sends a netlink message to configure NFSD listeners via
`nfsd_nl_listener_set_doit`, the kernel may need to delete existing listeners.
This is done by calling `svc_xprt_destroy_all()`, which iterates over the
transports and calls `svc_delete_xprt()` for each one.
Before fully destroying the transport, `svc_delete_xprt()` attempts to
unregister the service from the local `rpcbind` daemon by calling
`svc_register()` -> `rpcb_v4_register()`. This function performs a synchronous
RPC call to the local `rpcbind` UNIX socket (`/var/run/rpcbind.sock`).
If a malicious user sets up a fake, unresponsive `rpcbind` server (e.g., by
mounting a tmpfs over `/var/run` and binding a UNIX socket to that path), the
RPC call will block until it times out. The default timeout for local RPC
transports is 30 seconds (10 seconds base timeout with 2 retries). If multiple
listeners are being deleted simultaneously, these timeouts accumulate
sequentially (e.g., 5 listeners * 30 seconds = 150 seconds).
Because `nfsd_nl_listener_set_doit()` holds `nfsd_mutex` during this entire
process, any other task attempting to acquire `nfsd_mutex` (such as
`nfsd_nl_cache_flush_doit` seen in the crash trace) will be blocked for an
extended period, eventually triggering the kernel's hung task panic (which
defaults to 143 seconds in syzkaller).
**Exploitability:**
This is a pure Denial of Service (DoS) vulnerability. There is no memory
corruption, out-of-bounds access, or use-after-free involved. It cannot be used
for privilege escalation or information leaks.
**Accessibility:**
The bug can be triggered from an unprivileged process, provided it can create a
new user and network namespace. The `nfsd_nl_listener_set_doit` netlink command
requires `CAP_NET_ADMIN`, which a user can acquire within a new user/network
namespace. Furthermore, creating the fake `rpcbind` socket requires
`CAP_SYS_ADMIN` in the user namespace to mount a tmpfs over `/var/run`. Both of
these are standard capabilities available to unprivileged users utilizing user
namespaces. Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:false UserNamespace:true VMGuestTrigger:false VMHostTrigger:false]
|
| 1/1 |
2026/06/30 00:01 |
action |
syz-repro-to-c-repro |
0m
Results:
|
| 2/1 |
2026/06/30 00:01 |
action |
kernel-checkouter |
1m
Results: map[KernelSrc:/app/workdir/cache/src/72e9398d06801817b6455bb095de90682d844660]
|
| 3/1 |
2026/06/30 00:03 |
action |
kernel-builder |
23m
Results: map[KernelObj:/app/workdir/cache/build/4b2222202bfa81101d0722ae86eb9ab9cd03d42f]
|
| 4/1 |
2026/06/30 00:27 |
action |
codesearch-prepare |
17m
Results: map[Index:codesearch-index]
|
| 5/1 |
2026/06/30 00:45 |
agent |
expert |
10m
Model:
Results: map[DenialOfService:true Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:false UserNamespace:true VMGuestTrigger:false VMHostTrigger:false]
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 grepping
".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).
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, elevated privileges, or an information leak.
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 completely 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 transfers, that 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 exploitability depends on how exactly the uninit value
is used in the code, and what it affects.
Information leaks are exploitable on their own and should be classified as such. A bug that copies kernel
memory contents to userspace (e.g. an out-of-bounds read whose result is returned to the caller, or
uninitialized stack/heap bytes written to a user buffer) is exploitable: it can reveal kernel pointer
values and defeat KASLR, expose sensitive data such as cryptographic keys or other processes' memory, and
serves as a necessary building block in most modern kernel privilege-escalation exploit chains. Do not classify
an information leak as non-exploitable solely because it does not directly cause a memory write or control-flow
hijack; the leak itself is the exploit primitive.
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 Confidential 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.
Don't make assumptions about the kernel source code (it may be different from what you assume it is).
Extensively use the provided code access tools (codesearch-*, git-*, grepper, etc)
to examine the actual source code, and confirm any assumptions.
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:
INFO: task syz.0.9187:975 blocked for more than 143 seconds.
Tainted: G L syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.0.9187 state:D stack:28296 pid:975 tgid:974 ppid:31983 task_flags:0x400140 flags:0x00080002
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5510 [inline]
__schedule+0x125c/0x6730 kernel/sched/core.c:7234
__schedule_loop kernel/sched/core.c:7311 [inline]
schedule+0xdd/0x2c0 kernel/sched/core.c:7326
schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:7383
__mutex_lock_common kernel/locking/mutex.c:726 [inline]
__mutex_lock+0xccc/0x1bd0 kernel/locking/mutex.c:821
nfsd_nl_cache_flush_doit+0x137/0x230 fs/nfsd/nfsctl.c:2236
genl_family_rcv_msg_doit+0x214/0x300 net/netlink/genetlink.c:1114
genl_family_rcv_msg net/netlink/genetlink.c:1194 [inline]
genl_rcv_msg+0x560/0x800 net/netlink/genetlink.c:1209
netlink_rcv_skb+0x159/0x420 net/netlink/af_netlink.c:2556
genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218
netlink_unicast_kernel net/netlink/af_netlink.c:1319 [inline]
netlink_unicast+0x585/0x850 net/netlink/af_netlink.c:1345
netlink_sendmsg+0x8b0/0xda0 net/netlink/af_netlink.c:1900
sock_sendmsg_nosec net/socket.c:775 [inline]
__sock_sendmsg net/socket.c:790 [inline]
____sys_sendmsg+0xa4d/0xbe0 net/socket.c:2684
___sys_sendmsg+0x190/0x1e0 net/socket.c:2738
__sys_sendmsg+0x160/0x210 net/socket.c:2770
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f850619ce59
RSP: 002b:00007f8507096028 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007f8506415fa0 RCX: 00007f850619ce59
RDX: 0000000004000080 RSI: 0000200000000100 RDI: 0000000000000003
RBP: 00007f8506232e6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f8506416038 R14: 00007f8506415fa0 R15: 00007ffc2ad67f38
</TASK>
Showing all locks held in the system:
1 lock held by khungtaskd/31:
#0: ffffffff8e9e60c0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
#0: ffffffff8e9e60c0 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:840 [inline]
#0: ffffffff8e9e60c0 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x3d/0x184 kernel/locking/lockdep.c:6775
2 locks held by getty/5375:
#0: ffff8880375710a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x24/0x80 drivers/tty/tty_ldisc.c:243
#1: ffffc900032332e8 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: n_tty_read+0x419/0x14e0 drivers/tty/n_tty.c:2211
3 locks held by kworker/1:10/5748:
#0: ffff88801f6c0940 ((wq_completion)usb_hub_wq){+.+.}-{0:0}, at: process_one_work+0x12b1/0x1940 kernel/workqueue.c:3297
#1: ffffc90004f5fd08 ((work_completion)(&hub->events)){+.+.}-{0:0}, at: process_one_work+0x988/0x1940 kernel/workqueue.c:3298
#2: ffff88802bf981d8 (&dev->mutex){....}-{4:4}, at: device_lock include/linux/device.h:1102 [inline]
#2: ffff88802bf981d8 (&dev->mutex){....}-{4:4}, at: hub_event+0x1bd/0x4af0 drivers/usb/core/hub.c:5899
3 locks held by kworker/u9:1/26677:
#0: ffff888052dc0140 ((wq_completion)hci4){+.+.}-{0:0}, at: process_one_work+0x12b1/0x1940 kernel/workqueue.c:3297
#1: ffffc90007067d08 ((work_completion)(&hdev->error_reset)){+.+.}-{0:0}, at: process_one_work+0x988/0x1940 kernel/workqueue.c:3298
#2: ffff888093044ea0 (&hdev->req_lock){+.+.}-{4:4}, at: hci_dev_do_open+0x22/0xb0 net/bluetooth/hci_core.c:426
2 locks held by syz.5.9015/469:
#0: ffffffff908ed2e8 (cb_lock){++++}-{4:4}, at: genl_rcv+0x19/0x40 net/netlink/genetlink.c:1217
#1: ffffffff8ee6ffc0 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_nl_listener_set_doit+0xd5/0x1a80 fs/nfsd/nfsctl.c:1964
2 locks held by syz.0.9187/975:
#0: ffffffff908ed2e8 (cb_lock){++++}-{4:4}, at: genl_rcv+0x19/0x40 net/netlink/genetlink.c:1217
#1: ffffffff8ee6ffc0 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_nl_cache_flush_doit+0x137/0x230 fs/nfsd/nfsctl.c:2236
=============================================
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 31 Comm: khungtaskd Tainted: G L syzkaller #0 PREEMPT(full)
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
nmi_cpu_backtrace.cold+0x12d/0x151 lib/nmi_backtrace.c:122
nmi_trigger_cpumask_backtrace+0x21c/0x2a0 lib/nmi_backtrace.c:65
trigger_all_cpu_backtrace include/linux/nmi.h:162 [inline]
__sys_info lib/sys_info.c:157 [inline]
sys_info+0x141/0x190 lib/sys_info.c:165
check_hung_uninterruptible_tasks kernel/hung_task.c:353 [inline]
watchdog+0xcb1/0x1030 kernel/hung_task.c:561
kthread+0x370/0x450 kernel/kthread.c:436
ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 0 Comm: swapper/1 Tainted: G L syzkaller #0 PREEMPT(full)
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
RIP: 0010:pv_native_safe_halt+0xf/0x20 arch/x86/kernel/paravirt.c:64
Code: b6 a4 02 c3 cc cc cc cc 0f 1f 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 66 90 0f 00 2d 63 b9 2e 00 fb f4 <e9> bc 48 03 00 66 2e 0f 1f 84 00 00 00 00 00 66 90 90 90 90 90 90
RSP: 0018:ffffc90000197e00 EFLAGS: 00000246
RAX: 000000000874e1d7 RBX: ffff88801ea92540 RCX: ffffffff8b9ce2d5
RDX: 0000000000000000 RSI: ffffffff8e15d8b0 RDI: ffffffff8c3e9b80
RBP: ffffed1003d524a8 R08: 0000000000000001 R09: ffffed10170a678d
R10: ffff8880b8533c6b R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 1ffff92000032fc4 R15: dffffc0000000000
FS: 0000000000000000(0000) GS:ffff8881241e0000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b2f511ff8 CR3: 000000002dd66000 CR4: 00000000003526f0
Call Trace:
<TASK>
arch_safe_halt arch/x86/include/asm/paravirt.h:62 [inline]
default_idle+0x9/0x10 arch/x86/kernel/process.c:768
default_idle_call+0x6c/0xb0 kernel/sched/idle.c:122
cpuidle_idle_call kernel/sched/idle.c:199 [inline]
do_idle+0x3a7/0x5b0 kernel/sched/idle.c:355
cpu_startup_entry+0x4f/0x60 kernel/sched/idle.c:454
start_secondary+0x21d/0x2d0 arch/x86/kernel/smpboot.c:312
common_startup_64+0x13e/0x158
</TASK>
Reply: Based on the analysis of the bug report and the kernel source code, here is the assessment of the vulnerability:
**Bug Mechanism:**
The bug is a Denial of Service (DoS) caused by a long timeout while holding a global mutex (`nfsd_mutex`).
When a user sends a netlink message to configure NFSD listeners via `nfsd_nl_listener_set_doit`, the kernel may need to delete existing listeners. This is done by calling `svc_xprt_destroy_all()`, which iterates over the transports and calls `svc_delete_xprt()` for each one.
Before fully destroying the transport, `svc_delete_xprt()` attempts to unregister the service from the local `rpcbind` daemon by calling `svc_register()` -> `rpcb_v4_register()`. This function performs a synchronous RPC call to the local `rpcbind` UNIX socket (`/var/run/rpcbind.sock`).
If a malicious user sets up a fake, unresponsive `rpcbind` server (e.g., by mounting a tmpfs over `/var/run` and binding a UNIX socket to that path), the RPC call will block until it times out. The default timeout for local RPC transports is 30 seconds (10 seconds base timeout with 2 retries). If multiple listeners are being deleted simultaneously, these timeouts accumulate sequentially (e.g., 5 listeners * 30 seconds = 150 seconds).
Because `nfsd_nl_listener_set_doit()` holds `nfsd_mutex` during this entire process, any other task attempting to acquire `nfsd_mutex` (such as `nfsd_nl_cache_flush_doit` seen in the crash trace) will be blocked for an extended period, eventually triggering the kernel's hung task panic (which defaults to 143 seconds in syzkaller).
**Exploitability:**
This is a pure Denial of Service (DoS) vulnerability. There is no memory corruption, out-of-bounds access, or use-after-free involved. It cannot be used for privilege escalation or information leaks.
**Accessibility:**
The bug can be triggered from an unprivileged process, provided it can create a new user and network namespace. The `nfsd_nl_listener_set_doit` netlink command requires `CAP_NET_ADMIN`, which a user can acquire within a new user/network namespace. Furthermore, creating the fake `rpcbind` socket requires `CAP_SYS_ADMIN` in the user namespace to mount a tmpfs over `/var/run`. Both of these are standard capabilities available to unprivileged users utilizing user namespaces.
|
| 6/2 |
2026/06/30 00:45 |
llm |
expert |
0m
Model:
Tokens:
input: 9464
output: 47
thoughts: 697
Thoughts: **Analyzing a Hung NFSd Task**
Okay, I've got a hung task report here. It looks like `syz.0.9187:975` has been blocked for over 143 seconds. That's definitely concerning. The call trace shows a pretty standard path through the scheduler, indicating the kernel is trying to context switch but can't, which is expected. The interesting point is where the blockage occurs: `nfsd_nl_cache_flush_doit` within `fs/nfsd/nfsctl.c`. The trace points to a mutex, specifically `__mutex_lock` is where the hold-up is occuring.
My initial assumption, given my experience, is that we've got a mutex contention issue. Since the blocking function is `nfsd_nl_cache_flush_doit` and it's holding up the task, it means something is holding the `nfsd_mutex` that this function needs. I need to dive into the code for `nfsd_nl_cache_flush_doit` in `fs/nfsd/nfsctl.c` to see what resources it's trying to access. I need to figure out what might be causing the lock to be held for an extended period, or if the thread that holds the lock is stuck. Let's see what's happening there.
|
| 7/2 |
2026/06/30 00:45 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/nfsd/nfsctl.c Name:nfsd_nl_cache_flush_doit]
Results: map[SourceCode:2216: /**
2217: * nfsd_nl_cache_flush_doit - flush nfsd caches via netlink
2218: * @skb: reply buffer
2219: * @info: netlink metadata and command arguments
2220: *
2221: * Flush the svc_export and/or expkey caches. If NFSD_A_CACHE_FLUSH_MASK
2222: * is provided, only flush the caches indicated by the bitmask (bit 0 =
2223: * svc_export, bit 1 = expkey). If omitted, flush both.
2224: *
2225: * Return 0 on success or a negative errno.
2226: */
2227: int nfsd_nl_cache_flush_doit(struct sk_buff *skb, struct genl_info *info)
2228: {
2229: struct net *net = genl_info_net(info);
2230: struct nfsd_net *nn = net_generic(net, nfsd_net_id);
2231: u32 mask = ~0U;
2232:
2233: if (info->attrs[NFSD_A_CACHE_FLUSH_MASK])
2234: mask = nla_get_u32(info->attrs[NFSD_A_CACHE_FLUSH_MASK]);
2235:
2236: mutex_lock(&nfsd_mutex);
2237:
2238: if ((mask & NFSD_CACHE_TYPE_SVC_EXPORT) &&
2239: nn->svc_export_cache)
2240: cache_purge(nn->svc_export_cache);
2241:
2242: if ((mask & NFSD_CACHE_TYPE_EXPKEY) &&
2243: nn->svc_expkey_cache)
2244: cache_purge(nn->svc_expkey_cache);
2245:
2246: mutex_unlock(&nfsd_mutex);
2247:
2248: return 0;
2249: }
SourceFile:fs/nfsd/nfsctl.c]
|
| 8/2 |
2026/06/30 00:45 |
llm |
expert |
0m
Model:
Tokens:
input: 11116
output: 47
thoughts: 397
Thoughts: **Analyzing the NFSd Mutex Block**
Okay, so I've hit a snag. The task is currently stalled, waiting on `mutex_lock(&nfsd_mutex)`. Time to figure out who's got their hands on it. The bug report is helpful, let's see... Aha! I see two processes currently holding the `nfsd_mutex`. They are `syz.5.9015/469` and `syz.0.9187/975`. Both appear to have the `cb_lock` as well. That doesn't seem that unusual, but why are they holding up nfsd?
Specifically, it looks like `syz.5.9015/469` is holding the mutex at `nfsd_nl_listener_set_doit+0xd5/0x1a80`. Alright, that's the key. I need to take a closer look at `nfsd_nl_listener_set_doit`. Let's dig into that function and see what's going on.
|
| 9/2 |
2026/06/30 00:45 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/nfsd/nfsctl.c Name:nfsd_nl_listener_set_doit]
Results: map[SourceCode:1946: /**
1947: * nfsd_nl_listener_set_doit - set the nfs running sockets
1948: * @skb: reply buffer
1949: * @info: netlink metadata and command arguments
1950: *
1951: * Return 0 on success or a negative errno.
1952: */
1953: int nfsd_nl_listener_set_doit(struct sk_buff *skb, struct genl_info *info)
1954: {
1955: struct net *net = genl_info_net(info);
1956: struct svc_xprt *xprt, *tmp;
1957: const struct nlattr *attr;
1958: struct svc_serv *serv;
1959: LIST_HEAD(permsocks);
1960: struct nfsd_net *nn;
1961: bool delete = false;
1962: int err, rem;
1963:
1964: mutex_lock(&nfsd_mutex);
1965:
1966: err = nfsd_create_serv(net);
1967: if (err) {
1968: mutex_unlock(&nfsd_mutex);
1969: return err;
1970: }
1971:
1972: nn = net_generic(net, nfsd_net_id);
1973: serv = nn->nfsd_serv;
1974:
1975: spin_lock_bh(&serv->sv_lock);
1976:
1977: /* Move all of the old listener sockets to a temp list */
1978: list_splice_init(&serv->sv_permsocks, &permsocks);
1979:
1980: /*
1981: * Walk the list of server_socks from userland and move any that match
1982: * back to sv_permsocks
1983: */
1984: nlmsg_for_each_attr_type(attr, NFSD_A_SERVER_SOCK_ADDR, info->nlhdr,
1985: GENL_HDRLEN, rem) {
1986: struct nlattr *tb[NFSD_A_SOCK_MAX + 1];
1987: const char *xcl_name;
1988: struct sockaddr *sa;
1989:
1990: if (nla_parse_nested(tb, NFSD_A_SOCK_MAX, attr,
1991: nfsd_sock_nl_policy, info->extack) < 0)
1992: continue;
1993:
1994: if (!tb[NFSD_A_SOCK_ADDR] || !tb[NFSD_A_SOCK_TRANSPORT_NAME])
1995: continue;
1996:
1997: if (nla_len(tb[NFSD_A_SOCK_ADDR]) < sizeof(*sa))
1998: continue;
1999:
2000: xcl_name = nla_data(tb[NFSD_A_SOCK_TRANSPORT_NAME]);
2001: sa = nla_data(tb[NFSD_A_SOCK_ADDR]);
2002:
2003: /* Put back any matching sockets */
2004: list_for_each_entry_safe(xprt, tmp, &permsocks, xpt_list) {
2005: /* This shouldn't be possible */
2006: if (WARN_ON_ONCE(xprt->xpt_net != net)) {
2007: list_move(&xprt->xpt_list, &serv->sv_permsocks);
2008: continue;
2009: }
2010:
2011: /* If everything matches, put it back */
2012: if (!strcmp(xprt->xpt_class->xcl_name, xcl_name) &&
2013: rpc_cmp_addr_port(sa, (struct sockaddr *)&xprt->xpt_local)) {
2014: list_move(&xprt->xpt_list, &serv->sv_permsocks);
2015: break;
2016: }
2017: }
2018: }
2019:
2020: /*
2021: * If there are listener transports remaining on the permsocks list,
2022: * it means we were asked to remove a listener.
2023: */
2024: if (!list_empty(&permsocks)) {
2025: list_splice_init(&permsocks, &serv->sv_permsocks);
2026: delete = true;
2027: }
2028: spin_unlock_bh(&serv->sv_lock);
2029:
2030: /* Do not remove listeners while there are active threads. */
2031: if (serv->sv_nrthreads) {
2032: err = -EBUSY;
2033: goto out_unlock_mtx;
2034: }
2035:
2036: /*
2037: * Since we can't delete an arbitrary llist entry, destroy the
2038: * remaining listeners and recreate the list.
2039: */
2040: if (delete)
2041: svc_xprt_destroy_all(serv, net, false);
2042:
2043: /* walk list of addrs again, open any that still don't exist */
2044: nlmsg_for_each_attr_type(attr, NFSD_A_SERVER_SOCK_ADDR, info->nlhdr,
2045: GENL_HDRLEN, rem) {
2046: struct nlattr *tb[NFSD_A_SOCK_MAX + 1];
2047: const char *xcl_name;
2048: struct sockaddr *sa;
2049: int ret;
2050:
2051: if (nla_parse_nested(tb, NFSD_A_SOCK_MAX, attr,
2052: nfsd_sock_nl_policy, info->extack) < 0)
2053: continue;
2054:
2055: if (!tb[NFSD_A_SOCK_ADDR] || !tb[NFSD_A_SOCK_TRANSPORT_NAME])
2056: continue;
2057:
2058: if (nla_len(tb[NFSD_A_SOCK_ADDR]) < sizeof(*sa))
2059: continue;
2060:
2061: xcl_name = nla_data(tb[NFSD_A_SOCK_TRANSPORT_NAME]);
2062: sa = nla_data(tb[NFSD_A_SOCK_ADDR]);
2063:
2064: xprt = svc_find_listener(serv, xcl_name, net, sa);
2065: if (xprt) {
2066: if (delete)
2067: WARN_ONCE(1, "Transport type=%s already exists\n",
2068: xcl_name);
2069: svc_xprt_put(xprt);
2070: continue;
2071: }
2072:
2073: ret = svc_xprt_create_from_sa(serv, xcl_name, net, sa, 0,
2074: current_cred());
2075: /* always save the latest error */
2076: if (ret < 0)
2077: err = ret;
2078: }
2079:
2080: if (!serv->sv_nrthreads && list_empty(&nn->nfsd_serv->sv_permsocks))
2081: nfsd_destroy_serv(net);
2082:
2083: out_unlock_mtx:
2084: mutex_unlock(&nfsd_mutex);
2085:
2086: return err;
2087: }
SourceFile:fs/nfsd/nfsctl.c]
|
| 10/2 |
2026/06/30 00:45 |
llm |
expert |
0m
Model:
Tokens:
input: 14054
output: 44
thoughts: 252
Thoughts: **Analyzing the Potential for a Denial-of-Service Vulnerability in `nfsd_nl_listener_set_doit`**
Okay, let's break this down. My initial thought is focused on a loop within the `nfsd_nl_listener_set_doit` function. Specifically, it uses `nlmsg_for_each_attr_type` to iterate through attributes related to server socket addresses. My first concern is always the potential for an infinite loop. But no, `nlmsg_for_each_attr_type` only iterates over attributes present in the netlink message, so that's not the worry.
The loop does `nla_parse_nested` and then, if a `delete` flag is set, it calls `svc_xprt_destroy_all(serv, net, false)`. Now, the key question becomes, could `svc_xprt_destroy_all` itself be a blocking call? That's where I need to dig deeper. If `svc_xprt_destroy_all` takes a significant amount of time to complete for each attribute in this loop, it might be possible to construct a netlink message that exploits this, causing a denial of service. The attacker sends a large number of attributes, triggering a massive destruction of transports.
|
| 11/2 |
2026/06/30 00:45 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/nfsd/nfsctl.c Name:svc_xprt_destroy_all]
Results: map[SourceCode:1209: /**
1210: * svc_xprt_destroy_all - Destroy transports associated with @serv
1211: * @serv: RPC service to be shut down
1212: * @net: target network namespace
1213: * @unregister: true if it is OK to unregister the destroyed xprts
1214: *
1215: * Server threads may still be running (especially in the case where the
1216: * service is still running in other network namespaces).
1217: *
1218: * So we shut down sockets the same way we would on a running server, by
1219: * setting XPT_CLOSE, enqueuing, and letting a thread pick it up to do
1220: * the close. In the case there are no such other threads,
1221: * threads running, svc_clean_up_xprts() does a simple version of a
1222: * server's main event loop, and in the case where there are other
1223: * threads, we may need to wait a little while and then check again to
1224: * see if they're done.
1225: */
1226: void svc_xprt_destroy_all(struct svc_serv *serv, struct net *net,
1227: bool unregister)
1228: {
1229: int delay = 0;
1230:
1231: while (svc_close_list(serv, &serv->sv_permsocks, net) +
1232: svc_close_list(serv, &serv->sv_tempsocks, net)) {
1233:
1234: svc_clean_up_xprts(serv, net);
1235: msleep(delay++);
1236: }
1237:
1238: if (unregister)
1239: svc_rpcb_cleanup(serv, net);
1240: }
SourceFile:net/sunrpc/svc_xprt.c]
|
| 12/2 |
2026/06/30 00:45 |
llm |
expert |
0m
Model:
Tokens:
input: 15192
output: 41
thoughts: 131
Thoughts: **Analyzing the `svc_xprt_destroy_all` Function**
Okay, so I'm looking at `svc_xprt_destroy_all` and immediately a red flag pops up. There's a `while` loop here:
```c
while (svc_close_list(serv, &serv->sv_permsocks, net) +
svc_close_list(serv, &serv->sv_tempsocks, net)) {
svc_clean_up_xprts(serv, net);
msleep(delay++);
}
```
My concern is that if those `svc_close_list` calls *always* return a value greater than zero, this thing is going to get stuck in an infinite loop, slowly increasing the sleep delay. That's a definite possibility for resource exhaustion, and potentially a denial-of-service vulnerability. My immediate thought is, I need to understand what causes `svc_close_list` to return a value greater than zero. Time to dive into that function and see what's going on.
|
| 13/2 |
2026/06/30 00:45 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/sunrpc/svc_xprt.c Name:svc_close_list]
Results: map[SourceCode:1169: static int svc_close_list(struct svc_serv *serv, struct list_head *xprt_list, struct net *net)
1170: {
1171: struct svc_xprt *xprt;
1172: int ret = 0;
1173:
1174: spin_lock_bh(&serv->sv_lock);
1175: list_for_each_entry(xprt, xprt_list, xpt_list) {
1176: if (xprt->xpt_net != net)
1177: continue;
1178: ret++;
1179: set_bit(XPT_CLOSE, &xprt->xpt_flags);
1180: svc_xprt_enqueue(xprt);
1181: }
1182: spin_unlock_bh(&serv->sv_lock);
1183: return ret;
1184: }
SourceFile:net/sunrpc/svc_xprt.c]
|
| 14/2 |
2026/06/30 00:45 |
llm |
expert |
0m
Model:
Tokens:
input: 15896
output: 45
thoughts: 51
Thoughts: Here's my take on those thoughts, from an expert's perspective:
**Closing Network Transports**
Okay, so `svc_close_list` is all about shutting down a specific set of transports. It's essentially a targeted clean-up operation, filtering by network. The function is designed to return a count of the transports that are going to be closed, specifically those that match the `net` argument, which likely represents a network address or network interface.
The key action here is twofold: setting the `XPT_CLOSE` flag β a clear signal that the transport needs to gracefully shut down. This would trigger the appropriate state transitions within the transport's state machine, hopefully ensuring a clean close. Then, enqueuing them. That's how this is going to be managed. The enqueue likely puts them on a queue for later processing. It's probably handled asynchronously to avoid blocking the calling thread.
Finally, we're calling `svc_clean_up_xprts`. This is the part that does the *actual* work of closing those transports. Given the naming conventions, it probably handles the resources, socket closure, and removal from any transport lists. This two-step process allows for efficient, and potentially safe, closing of transports. It makes sense, keep things tidy.
|
| 15/2 |
2026/06/30 00:45 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/sunrpc/svc_xprt.c Name:svc_clean_up_xprts]
Results: map[SourceCode:1186: static void svc_clean_up_xprts(struct svc_serv *serv, struct net *net)
1187: {
1188: struct svc_xprt *xprt;
1189: int i;
1190:
1191: for (i = 0; i < serv->sv_nrpools; i++) {
1192: struct svc_pool *pool = &serv->sv_pools[i];
1193: struct llist_node *q, **t1, *t2;
1194:
1195: q = lwq_dequeue_all(&pool->sp_xprts);
1196: lwq_for_each_safe(xprt, t1, t2, &q, xpt_ready) {
1197: if (xprt->xpt_net == net) {
1198: set_bit(XPT_CLOSE, &xprt->xpt_flags);
1199: svc_delete_xprt(xprt);
1200: xprt = NULL;
1201: }
1202: }
1203:
1204: if (q)
1205: lwq_enqueue_batch(q, &pool->sp_xprts);
1206: }
1207: }
SourceFile:net/sunrpc/svc_xprt.c]
|
| 16/2 |
2026/06/30 00:45 |
llm |
expert |
0m
Model:
Tokens:
input: 16666
output: 43
thoughts: 69
Thoughts: **Analyzing the Exported Transport Cleanup Process**
Okay, so I'm looking at this `svc_clean_up_xprts` function, and my initial thought is, "Wait a minute, this is dequeuing from the `pool->sp_xprts` structure." Right, that makes sense for cleaning up old or unused transports. But then I see this condition: `if (xprt->xpt_net == net)`. That's the crux of it. If the network of the transport matches a certain criteria (represented by `net`), then `svc_delete_xprt(xprt)` is called on it. Hmm, that's where the real action happens. So, the question now is, what's happening within `svc_delete_xprt`? That function is what will contain the mechanism by which the particular `xprt` is freed, and it's essential for me to understand the consequences of calling it. I need to dig into `svc_delete_xprt` and see what resources are cleaned up and the implications for the broader export system. Let's see what that function does.
|
| 17/2 |
2026/06/30 00:45 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/sunrpc/svc_xprt.c Name:svc_delete_xprt]
Results: map[SourceCode:1104: /*
1105: * Remove a dead transport
1106: */
1107: static void svc_delete_xprt(struct svc_xprt *xprt)
1108: {
1109: struct svc_serv *serv = xprt->xpt_server;
1110: struct svc_deferred_req *dr;
1111:
1112: /* unregister with rpcbind for when transport type is TCP or UDP.
1113: */
1114: if (test_bit(XPT_RPCB_UNREG, &xprt->xpt_flags)) {
1115: struct svc_sock *svsk = container_of(xprt, struct svc_sock,
1116: sk_xprt);
1117: struct socket *sock = svsk->sk_sock;
1118:
1119: if (svc_register(serv, xprt->xpt_net, sock->sk->sk_family,
1120: sock->sk->sk_protocol, 0) < 0)
1121: pr_warn("failed to unregister %s with rpcbind\n",
1122: xprt->xpt_class->xcl_name);
1123: }
1124:
1125: if (test_and_set_bit(XPT_DEAD, &xprt->xpt_flags))
1126: return;
1127:
1128: trace_svc_xprt_detach(xprt);
1129: xprt->xpt_ops->xpo_detach(xprt);
1130: if (xprt->xpt_bc_xprt)
1131: xprt->xpt_bc_xprt->ops->close(xprt->xpt_bc_xprt);
1132:
1133: spin_lock_bh(&serv->sv_lock);
1134: list_del_init(&xprt->xpt_list);
1135: if (test_bit(XPT_TEMP, &xprt->xpt_flags) &&
1136: !test_bit(XPT_PEER_VALID, &xprt->xpt_flags))
1137: serv->sv_tmpcnt--;
1138: spin_unlock_bh(&serv->sv_lock);
1139:
1140: while ((dr = svc_deferred_dequeue(xprt)) != NULL)
1141: free_deferred(xprt, dr);
1142:
1143: call_xpt_users(xprt);
1144: svc_xprt_put(xprt);
1145: }
SourceFile:net/sunrpc/svc_xprt.c]
|
| 18/2 |
2026/06/30 00:45 |
llm |
expert |
0m
Model:
Tokens:
input: 17810
output: 43
thoughts: 258
Thoughts: **Deconstructing the Transport Deletion Process**
Okay, let me think this through. `svc_delete_xprt` is clearly the function responsible for removing a transport, specifically by calling `list_del_init(&xprt->xpt_list)`. That's the core of it - it's being pulled from either `serv->sv_permsocks` or `serv->sv_tempsocks`, which makes sense.
But here's where it gets interesting. `svc_close_list` is the function that iterates over this list, right? The very list we're deleting from! If `svc_delete_xprt` is doing its job, eventually `svc_close_list` should hit an empty list and return 0, causing the loop in `svc_xprt_destroy_all` to terminate. So, why would it *ever* keep returning a value greater than 0? Something's missing from my understanding here.
Aha! Now I see it. It looks like `svc_clean_up_xprts` dequeues things from `pool->sp_xprts`. If the transport isn't *in* `pool->sp_xprts`, `svc_clean_up_xprts` won't find it and won't call `svc_delete_xprt` which keeps the iteration going! So, I need to understand how the transports end up in `pool->sp_xprts` in the first place. That's the missing link.
Right... got it. `svc_close_list` calls `svc_xprt_enqueue(xprt)`. So, that function is populating the `pool->sp_xprts` queue! Now the pieces are beginning to fit...
|
| 19/2 |
2026/06/30 00:45 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/sunrpc/svc_xprt.c Name:svc_xprt_enqueue]
Results: map[SourceCode: 502: /**
503: * svc_xprt_enqueue - Queue a transport on an idle nfsd thread
504: * @xprt: transport with data pending
505: *
506: */
507: void svc_xprt_enqueue(struct svc_xprt *xprt)
508: {
509: struct svc_pool *pool;
510:
511: if (!svc_xprt_ready(xprt))
512: return;
513:
514: /* Mark transport as busy. It will remain in this state until
515: * the provider calls svc_xprt_received. We update XPT_BUSY
516: * atomically because it also guards against trying to enqueue
517: * the transport twice.
518: */
519: if (test_and_set_bit(XPT_BUSY, &xprt->xpt_flags))
520: return;
521:
522: pool = svc_pool_for_cpu(xprt->xpt_server);
523:
524: percpu_counter_inc(&pool->sp_sockets_queued);
525: xprt->xpt_qtime = ktime_get();
526: lwq_enqueue(&xprt->xpt_ready, &pool->sp_xprts);
527:
528: svc_pool_wake_idle_thread(pool);
529: }
SourceFile:net/sunrpc/svc_xprt.c]
|
| 20/2 |
2026/06/30 00:45 |
llm |
expert |
0m
Model:
Tokens:
input: 18970
output: 58
thoughts: 473
Thoughts: **The Infinite Loop in Transport Destruction**
Okay, let's break this down. `svc_xprt_enqueue` uses `test_and_set_bit(XPT_BUSY, &xprt->xpt_flags)`. If `XPT_BUSY` is already set, it bails out *immediately* and doesn't add the transport to `pool->sp_xprts`. That makes sense; it's protecting against double-processing. But here's the kicker: who's responsible for clearing `XPT_BUSY`? It's the thread that's processing the transport, likely through a call to `svc_xprt_received` or a similar function.
But wait a minute... `nfsd_nl_listener_set_doit` has a crucial check: it prevents removal of listeners if `serv->sv_nrthreads` is non-zero. The code comments also claim there are "active threads". So, if `serv->sv_nrthreads` *is* zero, then no active threads are running.
The issue then becomes, if there are no active threads, who clears `XPT_BUSY`? Nobody! The transport remains in a "busy" state indefinitely. `svc_xprt_enqueue` will see the busy state and just return without enqueuing it. Consequently, `svc_clean_up_xprts` won't find it in `pool->sp_xprts` because it was never enqueued to begin with, so `svc_delete_xprt` won't be called.
Then, `svc_close_list` will find the transport again in `sv_permsocks` or `sv_tempsocks` and return 1, and the loop in `svc_xprt_destroy_all` will continue indefinitely. *That's* an infinite loop!
I need to confirm whether `XPT_BUSY` can even be set when `sv_nrthreads == 0`. When a transport is created, is `XPT_BUSY` set? I need to check the transport creation logic.
|
| 21/2 |
2026/06/30 00:45 |
tool |
codesearch-find-references |
0m
Error:
Args: map[ContextFile:net/sunrpc/svc_xprt.c IncludeSnippetLines:2 Name:XPT_BUSY SourceTreePrefix:net/sunrpc]
Results: map[References:<nil> TruncatedOutput:false]
|
| 22/2 |
2026/06/30 00:45 |
llm |
expert |
0m
Model:
Tokens:
input: 19983
output: 29
thoughts: 22
Thoughts: Here's my thought process, as if I were thinking it:
**Digging into that `XPT_BUSY` Thing**
Okay, hold on a second. `XPT_BUSY`... that's ringing a bell, but I need to be precise here. It's either a macro or an enum, and I can't just assume. I need to be sure before I go any further, especially if I'm planning to use or modify it. So, let's fire up the search tools and hunt down where `XPT_BUSY` is actually defined. I want to see its context, how it's used, and what it *actually* represents in this system. That will be the key to interpreting this piece of code.
|
| 23/2 |
2026/06/30 00:45 |
tool |
grepper |
0m
Args: map[Expression:XPT_BUSY PathPrefix:net/sunrpc]
Results: map[Output:net/sunrpc/svc_xprt.c=45=static LIST_HEAD(svc_xprt_class_list);
--
net/sunrpc/svc_xprt.c-54- *
net/sunrpc/svc_xprt.c:55: * The XPT_BUSY bit in xprt->xpt_flags prevents a transport being
net/sunrpc/svc_xprt.c-56- * enqueued multiply. During normal transport processing this bit
--
net/sunrpc/svc_xprt.c-71- * XPT_DEAD:
net/sunrpc/svc_xprt.c:72: * - Can only be set while XPT_BUSY is held which ensures
net/sunrpc/svc_xprt.c-73- * that no other thread will be using the transport or will
--
net/sunrpc/svc_xprt.c=195=void svc_xprt_init(struct net *net, struct svc_xprt_class *xcl,
--
net/sunrpc/svc_xprt.c-207- spin_lock_init(&xprt->xpt_lock);
net/sunrpc/svc_xprt.c:208: set_bit(XPT_BUSY, &xprt->xpt_flags);
net/sunrpc/svc_xprt.c-209- xprt->xpt_net = get_net_track(net, &xprt->ns_tracker, GFP_ATOMIC);
--
net/sunrpc/svc_xprt.c=212=EXPORT_SYMBOL_GPL(svc_xprt_init);
--
net/sunrpc/svc_xprt.c-217- *
net/sunrpc/svc_xprt.c:218: * The caller must hold the XPT_BUSY bit and must
net/sunrpc/svc_xprt.c-219- * not thereafter touch transport data.
--
net/sunrpc/svc_xprt.c=224=void svc_xprt_received(struct svc_xprt *xprt)
net/sunrpc/svc_xprt.c-225-{
net/sunrpc/svc_xprt.c:226: if (!test_bit(XPT_BUSY, &xprt->xpt_flags)) {
net/sunrpc/svc_xprt.c-227- WARN_ONCE(1, "xprt=0x%p already busy!", xprt);
--
net/sunrpc/svc_xprt.c-235- smp_mb__before_atomic();
net/sunrpc/svc_xprt.c:236: clear_bit(XPT_BUSY, &xprt->xpt_flags);
net/sunrpc/svc_xprt.c-237-
--
net/sunrpc/svc_xprt.c-242- * with this check, the producer's own enqueue observes
net/sunrpc/svc_xprt.c:243: * !XPT_BUSY and dispatches the transport.
net/sunrpc/svc_xprt.c-244- */
--
net/sunrpc/svc_xprt.c=452=static void svc_xprt_resource_released(struct svc_xprt *xprt)
--
net/sunrpc/svc_xprt.c-458- if (xpt_flags & (BIT(XPT_DATA) | BIT(XPT_DEFERRED)) &&
net/sunrpc/svc_xprt.c:459: !(xpt_flags & BIT(XPT_BUSY)))
net/sunrpc/svc_xprt.c-460- svc_xprt_enqueue(xprt);
--
net/sunrpc/svc_xprt.c=472=static bool svc_xprt_ready(struct svc_xprt *xprt)
--
net/sunrpc/svc_xprt.c-487- trace_svc_xprt_enqueue(xprt, xpt_flags);
net/sunrpc/svc_xprt.c:488: if (xpt_flags & BIT(XPT_BUSY))
net/sunrpc/svc_xprt.c-489- return false;
--
net/sunrpc/svc_xprt.c=507=void svc_xprt_enqueue(struct svc_xprt *xprt)
--
net/sunrpc/svc_xprt.c-514- /* Mark transport as busy. It will remain in this state until
net/sunrpc/svc_xprt.c:515: * the provider calls svc_xprt_received. We update XPT_BUSY
net/sunrpc/svc_xprt.c-516- * atomically because it also guards against trying to enqueue
--
net/sunrpc/svc_xprt.c-518- */
net/sunrpc/svc_xprt.c:519: if (test_and_set_bit(XPT_BUSY, &xprt->xpt_flags))
net/sunrpc/svc_xprt.c-520- return;
--
net/sunrpc/svc_xprt.c=832=static void svc_handle_xprt(struct svc_rqst *rqstp, struct svc_xprt *xprt)
--
net/sunrpc/svc_xprt.c-840- svc_delete_xprt(xprt);
net/sunrpc/svc_xprt.c:841: /* Leave XPT_BUSY set on the dead xprt: */
net/sunrpc/svc_xprt.c-842- goto out;
--
net/sunrpc/svc_xprt.c=1018=static void svc_age_temp_xprts(struct timer_list *t)
--
net/sunrpc/svc_xprt.c-1040- if (kref_read(&xprt->xpt_ref) > 1 ||
net/sunrpc/svc_xprt.c:1041: test_bit(XPT_BUSY, &xprt->xpt_flags))
net/sunrpc/svc_xprt.c-1042- continue;
--
net/sunrpc/svc_xprt.c=1152=void svc_xprt_close(struct svc_xprt *xprt)
--
net/sunrpc/svc_xprt.c-1155- set_bit(XPT_CLOSE, &xprt->xpt_flags);
net/sunrpc/svc_xprt.c:1156: if (test_and_set_bit(XPT_BUSY, &xprt->xpt_flags))
net/sunrpc/svc_xprt.c-1157- /* someone else will have to effect the close */
]
|
| 24/2 |
2026/06/30 00:45 |
llm |
expert |
0m
Model:
Tokens:
input: 21981
output: 47
thoughts: 231
Thoughts: **Analyzing the Lifecycle of `XPT_BUSY` in the NFS Server**
Okay, so `svc_xprt_init` kicks things off by setting the `XPT_BUSY` flag β pretty straightforward:
```c
set_bit(XPT_BUSY, &xprt->xpt_flags);
```
My immediate question is: *when* is this flag cleared? A quick scan reveals that `svc_xprt_received` seems to be responsible for unsetting it. That seems sensible, a received message implies the transport is no longer busy with initialization.
But hereβs where things get interesting. I see that `nfsd_nl_listener_set_doit` calls `svc_xprt_create_from_sa`. Now I have to pause. What happens to `XPT_BUSY` in this scenario? If `svc_xprt_create_from_sa` *fails* later, is `XPT_BUSY` cleared? What if it *succeeds*? Does it return a transport with `XPT_BUSY` set? I donβt think so. I suspect `svc_xprt_create_from_sa` likely clears it itself, or perhaps enqueues something that will eventually clear it.
I need to drill down into `svc_xprt_create_from_sa` to be certain. I need to understand its behavior around `XPT_BUSY`. Letβs go check the code.
|
| 25/2 |
2026/06/30 00:46 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/sunrpc/svc_xprt.c Name:svc_xprt_create_from_sa]
Results: map[SourceCode: 301: /**
302: * svc_xprt_create_from_sa - Add a new listener to @serv from socket address
303: * @serv: target RPC service
304: * @xprt_name: transport class name
305: * @net: network namespace
306: * @sap: socket address pointer
307: * @flags: SVC_SOCK flags
308: * @cred: credential to bind to this transport
309: *
310: * Return local xprt port on success or %-EPROTONOSUPPORT on failure
311: */
312: int svc_xprt_create_from_sa(struct svc_serv *serv, const char *xprt_name,
313: struct net *net, struct sockaddr *sap,
314: int flags, const struct cred *cred)
315: {
316: size_t len;
317: int err;
318:
319: switch (sap->sa_family) {
320: case AF_INET:
321: len = sizeof(struct sockaddr_in);
322: break;
323: #if IS_ENABLED(CONFIG_IPV6)
324: case AF_INET6:
325: len = sizeof(struct sockaddr_in6);
326: break;
327: #endif
328: default:
329: return -EAFNOSUPPORT;
330: }
331:
332: err = _svc_xprt_create(serv, xprt_name, net, sap, len, flags, cred);
333: if (err == -EPROTONOSUPPORT) {
334: request_module("svc%s", xprt_name);
335: err = _svc_xprt_create(serv, xprt_name, net, sap, len, flags,
336: cred);
337: }
338:
339: return err;
340: }
SourceFile:net/sunrpc/svc_xprt.c]
|
| 26/2 |
2026/06/30 00:46 |
llm |
expert |
0m
Model:
Tokens:
input: 23213
output: 44
thoughts: 14
Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience and written in the first person:
**Diving into `_svc_xprt_create`**
Alright, let's get down to brass tacks. I need to refresh my memory on the innards of this thing β specifically, `_svc_xprt_create`. My intuition is nudging me to examine the core transport creation logic. Whatβs the instantiation process look like here? Is it properly handling all the relevant parameters? I need to drill down into how it allocates and initializes resources for a new service transport. Are there any obvious potential vulnerabilities or areas for optimization jumping out? I'm anticipating that understanding the intricacies of transport creation is going to be key to debugging this particular issue. Gotta check the arguments, the memory management... and what about any potential race conditions? Let's get to it!
|
| 27/2 |
2026/06/30 00:46 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/sunrpc/svc_xprt.c Name:_svc_xprt_create]
Results: map[SourceCode: 263: static int _svc_xprt_create(struct svc_serv *serv, const char *xprt_name,
264: struct net *net, struct sockaddr *sap,
265: size_t len, int flags, const struct cred *cred)
266: {
267: struct svc_xprt_class *xcl;
268:
269: spin_lock(&svc_xprt_class_lock);
270: list_for_each_entry(xcl, &svc_xprt_class_list, xcl_list) {
271: struct svc_xprt *newxprt;
272: unsigned short newport;
273:
274: if (strcmp(xprt_name, xcl->xcl_name))
275: continue;
276:
277: if (!try_module_get(xcl->xcl_owner))
278: goto err;
279:
280: spin_unlock(&svc_xprt_class_lock);
281: newxprt = xcl->xcl_ops->xpo_create(serv, net, sap, len, flags);
282: if (IS_ERR(newxprt)) {
283: trace_svc_xprt_create_err(serv->sv_programs->pg_name,
284: xcl->xcl_name, sap, len,
285: newxprt);
286: module_put(xcl->xcl_owner);
287: return PTR_ERR(newxprt);
288: }
289: newxprt->xpt_cred = get_cred(cred);
290: svc_add_new_perm_xprt(serv, newxprt);
291: newport = svc_xprt_local_port(newxprt);
292: return newport;
293: }
294: err:
295: spin_unlock(&svc_xprt_class_lock);
296: /* This errno is exposed to user space. Provide a reasonable
297: * perror msg for a bad transport. */
298: return -EPROTONOSUPPORT;
299: }
SourceFile:net/sunrpc/svc_xprt.c]
|
| 28/2 |
2026/06/30 00:46 |
llm |
expert |
0m
Model:
Tokens:
input: 24141
output: 47
thoughts: 17
Thoughts: Okay, here's my attempt at summarizing that thought process, keeping in mind I'm speaking to a fellow expert:
**Diving into `svc_add_new_perm_xprt`**
Alright, time to dig into `svc_add_new_perm_xprt`. I'm going to take a look at how that function operates. It's a critical piece of the system, so I need to understand its behavior thoroughly, especially given the context of what we're working on. Let's see how it adds and manages new permissions. I'll focus on the data structures it uses, the locking it employs, and any potential race conditions that might exist. I'll need to remember any similar implementations I've worked with in the past to identify potential pitfalls quickly. Let's start with a systematic walkthrough and see where this takes us.
|
| 29/2 |
2026/06/30 00:46 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/sunrpc/svc_xprt.c Name:svc_add_new_perm_xprt]
Results: map[SourceCode: 254: void svc_add_new_perm_xprt(struct svc_serv *serv, struct svc_xprt *new)
255: {
256: clear_bit(XPT_TEMP, &new->xpt_flags);
257: spin_lock_bh(&serv->sv_lock);
258: list_add(&new->xpt_list, &serv->sv_permsocks);
259: spin_unlock_bh(&serv->sv_lock);
260: svc_xprt_received(new);
261: }
SourceFile:net/sunrpc/svc_xprt.c]
|
| 30/2 |
2026/06/30 00:46 |
llm |
expert |
0m
Model:
Tokens:
input: 24582
output: 43
thoughts: 688
Thoughts: **Debugging a Potential Infinite Loop**
Okay, let's break this down. My initial thought was, "Aha! `svc_add_new_perm_xprt` triggers `svc_xprt_received(new)`, which clears `XPT_BUSY`!". That's good. But, *wait*, if `XPT_BUSY` is cleared, then `svc_close_list` *should* set `XPT_CLOSE` and call `svc_xprt_enqueue`. Since the `XPT_BUSY` flag is clear, `svc_xprt_enqueue` should set `XPT_BUSY` and enqueue the transport to `pool->sp_xprts`. Then, the `svc_clean_up_xprts` function should come along, find the transport in `pool->sp_xprts` and call `svc_delete_xprt`. In theory, that *should* all work as expected!
But, something is clearly wrong, because I'm seeing `svc_xprt_destroy_all` loop forever. Time to dig deeper. I'm going to revisit `svc_close_list` code to see if the issue is there.
```c
static int svc_close_list(struct svc_serv *serv, struct list_head *xprt_list, struct net *net)
{
struct svc_xprt *xprt;
int ret = 0;
spin_lock_bh(&serv->sv_lock);
list_for_each_entry(xprt, xprt_list, xpt_list) {
if (xprt->xpt_net != net)
continue;
ret++;
set_bit(XPT_CLOSE, &xprt->xpt_flags);
svc_xprt_enqueue(xprt);
}
spin_unlock_bh(&serv->sv_lock);
return ret;
}
```
Okay, the loop itself *looks* sound. The issue must lie within `svc_xprt_enqueue` itself. If `svc_xprt_enqueue` fails to properly enqueue something, it could cause this infinite loop.
So, let's check `svc_xprt_enqueue` to see if there is an issue:
```c
void svc_xprt_enqueue(struct svc_xprt *xprt)
{
struct svc_pool *pool;
if (!svc_xprt_ready(xprt))
return;
/* Mark transport as busy. It will remain in this state until
* the provider calls svc_xprt_received. We update XPT_BUSY
* atomically because it also guards against trying to enqueue
* the transport twice.
*/
if (test_and_set_bit(XPT_BUSY, &xprt->xpt_flags))
return;
pool = svc_pool_for_cpu(xprt->xpt_server);
percpu_counter_inc(&pool->sp_sockets_queued);
xprt->xpt_qtime = ktime_get();
lwq_enqueue(&xprt->xpt_ready, &pool->sp_xprts);
svc_pool_wake_idle_thread(pool);
}
```
Ah! Got it! If `!svc_xprt_ready(xprt)` returns true, `svc_xprt_enqueue` immediately returns without enqueuing! That's the likely culprit for the infinite loop, I need to check the conditions within `svc_xprt_ready` and ensure that I am ready for the transport to be enqueued.
|
| 31/2 |
2026/06/30 00:46 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/sunrpc/svc_xprt.c Name:svc_xprt_ready]
Results: map[SourceCode: 472: static bool svc_xprt_ready(struct svc_xprt *xprt)
473: {
474: unsigned long xpt_flags;
475:
476: /*
477: * If another cpu has recently updated xpt_flags,
478: * sk_sock->flags, xpt_reserved, or xpt_nr_rqsts, we need to
479: * know about it; otherwise it's possible that both that cpu and
480: * this one could call svc_xprt_enqueue() without either
481: * svc_xprt_enqueue() recognizing that the conditions below
482: * are satisfied, and we could stall indefinitely:
483: */
484: smp_rmb();
485: xpt_flags = READ_ONCE(xprt->xpt_flags);
486:
487: trace_svc_xprt_enqueue(xprt, xpt_flags);
488: if (xpt_flags & BIT(XPT_BUSY))
489: return false;
490: if (xpt_flags & (BIT(XPT_CONN) | BIT(XPT_CLOSE) | BIT(XPT_HANDSHAKE)))
491: return true;
492: if (xpt_flags & (BIT(XPT_DATA) | BIT(XPT_DEFERRED))) {
493: if (xprt->xpt_ops->xpo_has_wspace(xprt) &&
494: svc_xprt_slots_in_range(xprt))
495: return true;
496: trace_svc_xprt_no_write_space(xprt);
497: return false;
498: }
499: return false;
500: }
SourceFile:net/sunrpc/svc_xprt.c]
|
| 32/2 |
2026/06/30 00:46 |
llm |
expert |
0m
Model:
Tokens:
input: 26711
output: 39
thoughts: 570
Thoughts: **Analyzing a Potential Infinite Loop in Transport Handling**
Okay, so I'm looking at this `svc_xprt_ready` function, and it's immediately clear that it returns `false` if the `XPT_BUSY` flag is set in `xpt_flags`. This makes sense, a busy transport shouldn't be considered "ready". So `svc_xprt_enqueue` will bail out right away if `XPT_BUSY` is true, which seems correct.
Now, if `XPT_BUSY` isn't set, `svc_xprt_ready` checks for `XPT_CLOSE`. `svc_close_list` *just* set `XPT_CLOSE`, so the check is going to return `true` this time. This is where it gets interesting... `svc_xprt_enqueue` sets `XPT_BUSY` and enqueues the transport. So, that flow seems fine when the transport isn't busy.
But what happens when `XPT_BUSY` *is* set? Well, `svc_xprt_ready` returns `false`, `svc_xprt_enqueue` does nothing. This means the transport *won't* be found by `svc_clean_up_xprts` in `pool->sp_xprts`, so it won't be deleted, it stays in the list.
Now, `svc_close_list` will find it again, see that `XPT_CLOSE` is already set, and call `svc_xprt_enqueue`. But `svc_xprt_enqueue` will, *again*, return immediately because `XPT_BUSY` is set! Bingo. This is an infinite loop right there! It keeps getting enqueued because the busy flag is not unset.
The core question now becomes: how can `XPT_BUSY` be set when `svc_xprt_destroy_all` is called? I see that `nfsd_nl_listener_set_doit` calls `svc_xprt_destroy_all(serv, net, false)`. And before calling this, it checks to see if any threads are active. If `serv->sv_nrthreads` is non-zero, it returns an error. So we're supposed to be in a situation where there are no active threads.
So, if there are no threads, could a transport somehow still have `XPT_BUSY` set? Let's see: maybe if a transport was created but not fully initialized? No. `svc_add_new_perm_xprt` clears `XPT_BUSY`. So that's not it.
What if a transport was enqueued to `pool->sp_xprts` previously, and a thread picked it up, set `XPT_BUSY`, but then the thread exited? Yes! When a thread picks up a transport, it sets `XPT_BUSY`. Looks like the flow in `svc_recv` needs some careful attention, I'm going to have to dive into that next.
|
| 33/2 |
2026/06/30 00:46 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/sunrpc/svc_xprt.c Name:svc_recv]
Results: map[SourceCode: 904: /**
905: * svc_recv - Receive and process the next request on any transport
906: * @rqstp: an idle RPC service thread
907: * @timeo: timeout (in jiffies) (0 means infinite timeout)
908: *
909: * This code is carefully organised not to touch any cachelines in
910: * the shared svc_serv structure, only cachelines in the local
911: * svc_pool.
912: *
913: * If the timeout is 0, then the sleep will never time out.
914: *
915: * Returns -ETIMEDOUT if idle for an extended period
916: * -EBUSY if there is more work to do than available threads
917: * 0 otherwise.
918: */
919: int svc_recv(struct svc_rqst *rqstp, long timeo)
920: {
921: struct svc_pool *pool = rqstp->rq_pool;
922: bool did_timeout;
923: int ret = 0;
924:
925: if (!svc_alloc_arg(rqstp))
926: return ret;
927:
928: did_timeout = svc_thread_wait_for_work(rqstp, timeo);
929:
930: if (did_timeout && svc_thread_should_sleep(rqstp) &&
931: pool->sp_nrthrmin && pool->sp_nrthreads > pool->sp_nrthrmin)
932: ret = -ETIMEDOUT;
933:
934: clear_bit(SP_TASK_PENDING, &pool->sp_flags);
935:
936: if (svc_thread_should_stop(rqstp)) {
937: svc_thread_wake_next(rqstp);
938: return ret;
939: }
940:
941: rqstp->rq_xprt = svc_xprt_dequeue(pool);
942: if (rqstp->rq_xprt) {
943: struct svc_xprt *xprt = rqstp->rq_xprt;
944:
945: svc_thread_wake_next(rqstp);
946: /* Normally we will wait up to 5 seconds for any required
947: * cache information to be provided. When there are no
948: * idle threads, we reduce the wait time.
949: */
950: if (pool->sp_idle_threads.first) {
951: rqstp->rq_chandle.thread_wait = 5 * HZ;
952: } else {
953: rqstp->rq_chandle.thread_wait = 1 * HZ;
954: /*
955: * No idle threads: signal -EBUSY so the caller
956: * can consider spawning another thread. Use
957: * SP_TASK_STARTING to limit this signal to one
958: * thread at a time; the caller clears this flag
959: * after starting a new thread.
960: */
961: if (!did_timeout && timeo &&
962: !test_and_set_bit(SP_TASK_STARTING,
963: &pool->sp_flags))
964: ret = -EBUSY;
965: }
966:
967: trace_svc_xprt_dequeue(rqstp);
968: svc_handle_xprt(rqstp, xprt);
969: }
970:
971: #if defined(CONFIG_SUNRPC_BACKCHANNEL)
972: if (svc_is_backchannel(rqstp)) {
973: struct svc_serv *serv = rqstp->rq_server;
974: struct rpc_rqst *req;
975:
976: req = lwq_dequeue(&serv->sv_cb_list,
977: struct rpc_rqst, rq_bc_list);
978: if (req) {
979: svc_thread_wake_next(rqstp);
980: svc_process_bc(req, rqstp);
981: }
982: }
983: #endif
984: return ret;
985: }
SourceFile:net/sunrpc/svc_xprt.c]
|
| 34/2 |
2026/06/30 00:46 |
llm |
expert |
0m
Model:
Tokens:
input: 29296
output: 43
thoughts: 82
Thoughts: Okay, let me think this through.
**Deconstructing the `svc_xprt_dequeue` Function**
Right, so `svc_xprt_dequeue` is responsible for removing a transport from `pool->sp_xprts`. My initial thought is, does it handle clearing the `XPT_BUSY` flag? The documentation isn't immediately clear on this. Ah, no, that doesn't seem to be the case. I recall now that `XPT_BUSY` is actually handled either in `svc_xprt_received` or potentially `svc_handle_xprt`. It makes sense the state would be managed at the receiving or handling stage. Let's dig into `svc_handle_xprt` to confirm. I think that's where I need to look to be absolutely sure. I need to refresh my memory on the flow of control.
|
| 35/2 |
2026/06/30 00:46 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/sunrpc/svc_xprt.c Name:svc_handle_xprt]
Results: map[SourceCode: 832: static void svc_handle_xprt(struct svc_rqst *rqstp, struct svc_xprt *xprt)
833: {
834: struct svc_serv *serv = rqstp->rq_server;
835: int len = 0;
836:
837: if (test_bit(XPT_CLOSE, &xprt->xpt_flags)) {
838: if (test_and_clear_bit(XPT_KILL_TEMP, &xprt->xpt_flags))
839: xprt->xpt_ops->xpo_kill_temp_xprt(xprt);
840: svc_delete_xprt(xprt);
841: /* Leave XPT_BUSY set on the dead xprt: */
842: goto out;
843: }
844: if (test_bit(XPT_LISTENER, &xprt->xpt_flags)) {
845: struct svc_xprt *newxpt;
846: /*
847: * We know this module_get will succeed because the
848: * listener holds a reference too
849: */
850: __module_get(xprt->xpt_class->xcl_owner);
851: svc_check_conn_limits(xprt->xpt_server);
852: newxpt = xprt->xpt_ops->xpo_accept(xprt);
853: if (newxpt) {
854: newxpt->xpt_cred = get_cred(xprt->xpt_cred);
855: svc_add_new_temp_xprt(serv, newxpt);
856: trace_svc_xprt_accept(newxpt, serv->sv_name);
857: } else {
858: module_put(xprt->xpt_class->xcl_owner);
859: }
860: svc_xprt_received(xprt);
861: } else if (test_bit(XPT_HANDSHAKE, &xprt->xpt_flags)) {
862: xprt->xpt_ops->xpo_handshake(xprt);
863: svc_xprt_received(xprt);
864: } else if (svc_xprt_reserve_slot(rqstp, xprt)) {
865: /* XPT_DATA|XPT_DEFERRED case: */
866: rqstp->rq_deferred = svc_deferred_dequeue(xprt);
867: if (rqstp->rq_deferred)
868: len = svc_deferred_recv(rqstp);
869: else
870: len = xprt->xpt_ops->xpo_recvfrom(rqstp);
871: rqstp->rq_reserved = serv->sv_max_mesg;
872: atomic_add(rqstp->rq_reserved, &xprt->xpt_reserved);
873: if (len <= 0)
874: goto out;
875:
876: trace_svc_xdr_recvfrom(&rqstp->rq_arg);
877:
878: clear_bit(XPT_OLD, &xprt->xpt_flags);
879:
880: rqstp->rq_chandle.defer = svc_defer;
881:
882: if (serv->sv_stats)
883: serv->sv_stats->netcnt++;
884: percpu_counter_inc(&rqstp->rq_pool->sp_messages_arrived);
885: rqstp->rq_stime = ktime_get();
886: svc_process(rqstp);
887: } else
888: svc_xprt_received(xprt);
889:
890: out:
891: rqstp->rq_res.len = 0;
892: svc_xprt_release(rqstp);
893: }
SourceFile:net/sunrpc/svc_xprt.c]
|
| 36/2 |
2026/06/30 00:46 |
llm |
expert |
0m
Model:
Tokens:
input: 30795
output: 42
thoughts: 367
Thoughts: **Analyzing Transport Closure in NFSd**
Okay, so I'm looking at this `svc_handle_xprt` function, specifically this section here. If the `XPT_CLOSE` flag is set on the transport, it triggers `svc_delete_xprt(xprt)`. The code indicates that `XPT_BUSY` is deliberately left set after this deletion.
Now, `svc_delete_xprt` removes the transport from the `sv_permsocks` and `sv_tempsocks` lists. That's fine, it makes sense. It means `svc_close_list` won't find it anymore, which is what we expect. But something about this is nagging at me.
What happens if a transport was enqueued in `pool->sp_xprts` *before* the `XPT_CLOSE` flag was set, indicating work for it to do, but no thread ever actually picked it up? Essentially `XPT_BUSY` is set, but no thread processes it. This could happen due to a race condition.
And what if, after it's enqueued (so `XPT_BUSY` is set), *all* threads are stopped? That would make `sv_nrthreads` zero, but the transport is still sitting there. Then `svc_delete_xprt` is called on that transport with `XPT_BUSY` still set!
The question is, when threads are stopped, does the system clear the `pool->sp_xprts` queue? I'm not seeing any explicit cleanup here. This scenario could lead to a dangling transport. I need to investigate the `nfsd_destroy_serv` function or the thread stopping routines to confirm whether `pool->sp_xprts` is properly handled during thread shutdown. Otherwise, this might be a potential resource leak or a source of unexpected behavior.
|
| 37/2 |
2026/06/30 00:46 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/nfsd/nfsctl.c Name:nfsd_destroy_serv]
Results: map[SourceCode: 498: /**
499: * nfsd_destroy_serv - tear down NFSD's svc_serv for a namespace
500: * @net: network namespace the NFS service is associated with
501: */
502: void nfsd_destroy_serv(struct net *net)
503: {
504: struct nfsd_net *nn = net_generic(net, nfsd_net_id);
505: struct svc_serv *serv = nn->nfsd_serv;
506:
507: lockdep_assert_held(&nfsd_mutex);
508:
509: spin_lock(&nfsd_notifier_lock);
510: nn->nfsd_serv = NULL;
511: spin_unlock(&nfsd_notifier_lock);
512:
513: /* check if the notifier still has clients */
514: if (atomic_dec_return(&nfsd_notifier_refcount) == 0) {
515: unregister_inetaddr_notifier(&nfsd_inetaddr_notifier);
516: #if IS_ENABLED(CONFIG_IPV6)
517: unregister_inet6addr_notifier(&nfsd_inet6addr_notifier);
518: #endif
519: }
520:
521: /*
522: * write_ports can create the server without actually starting
523: * any threads. If we get shut down before any threads are
524: * started, then nfsd_destroy_serv will be run before any of this
525: * other initialization has been done except the rpcb information.
526: */
527: svc_xprt_destroy_all(serv, net, true);
528: nfsd_shutdown_net(net);
529: svc_destroy(&serv);
530: }
SourceFile:fs/nfsd/nfssvc.c]
|
| 38/2 |
2026/06/30 00:46 |
llm |
expert |
0m
Model:
Tokens:
input: 32181
output: 44
thoughts: 617
Thoughts: **Analyzing a Potential NFS Server Hang**
Okay, so I'm diving into this `nfsd_destroy_serv` function, and it's calling `svc_xprt_destroy_all` with this `serv` and `net` parameter, along with a `true` flag. I immediately notice that if `sv_nrthreads` is zero, we're definitely hitting `svc_xprt_destroy_all`. That's my starting point.
Now, my mind starts racing. The code comments mention a potential problem: if transports within `sv_permsocks` have `XPT_BUSY` set, *but* they aren't in `pool->sp_xprts`, we can get an infinite loop in `svc_xprt_destroy_all`. That's a nasty condition. So, I need to figure out how that situation *could* happen.
Let's dissect it. First, `svc_xprt_init` sets `XPT_BUSY`, so newly initialized transports have this flag set. However, `svc_add_new_perm_xprt` *clears* `XPT_BUSY` by calling `svc_xprt_received(new)`. So, a freshly created transport *doesn't* have `XPT_BUSY` set initially. Got it.
But what if `svc_xprt_enqueue` comes into play? Ah, yes! `svc_xprt_enqueue` *does* set `XPT_BUSY` and, crucially, enqueues the transport to `pool->sp_xprts`. If it's *in* `pool->sp_xprts`, the `svc_clean_up_xprts` function should find it, set `XPT_CLOSE`, and then call `svc_delete_xprt`, which will remove it from `sv_permsocks`. So, under normal operation, it *should* be removed.
Hold on, there's a wrinkle! What if `svc_clean_up_xprts` *dequeues* a transport from `pool->sp_xprts`, but its `xprt->xpt_net` is *not* equal to `net`? The code block is crucial here:
```c
q = lwq_dequeue_all(&pool->sp_xprts);
lwq_for_each_safe(xprt, t1, t2, &q, xpt_ready) {
if (xprt->xpt_net == net) {
set_bit(XPT_CLOSE, &xprt->xpt_flags);
svc_delete_xprt(xprt);
xprt = NULL;
}
}
if (q)
lwq_enqueue_batch(q, &pool->sp_xprts);
```
Okay, the code dequeues everything to `q`. Then, it iterates, and if the network matches (`xprt->xpt_net == net`), it marks it for closure and removes it. But if the network doesn't match it leaves it in `q` and enqueues the contents of `q` *back* to `pool->sp_xprts`. That sounds potentially problematic...
But wait! `lwq_for_each_safe` iterates over `q`. And if `xprt->xpt_net == net`, it sets `xprt = NULL`. This means it *should* be removed. Okay, time to check how that `lwq_for_each_safe` macro works under the hood because that part is still a little fuzzy, and I need to make *sure* it handles the NULL assignment correctly. Let me pull that up...
|
| 39/2 |
2026/06/30 00:46 |
tool |
codesearch-definition-source |
0m
Error:
Args: map[ContextFile:net/sunrpc/svc_xprt.c Name:lwq_for_each_safe]
Results: map[SourceCode: SourceFile:]
|
| 40/2 |
2026/06/30 00:46 |
llm |
expert |
0m
Model:
Tokens:
input: 33704
output: 28
thoughts: 15
Thoughts: Okay, here's my attempt at summarizing that thought process, keeping in mind I'm supposed to speak as a seasoned expert:
**Investigating `lwq_for_each_safe`**
Right, let's dive into this. The mental checklist starts with, "Okay, `lwq_for_each_safe`β¦ what's the context?" Immediately, my mind is searching for the likely application. Given the naming convention, I'm already anticipating this is going to be some form of a linked list or container iteration, likely within the kernel or a low-level system component. The "safe" aspect is crucial; that screams out "concurrent modification avoidance" at me. My intuition is that this is the mechanism being used to traverse a data structure where the structure itself could be modified by another thread or process *during* the traversal. We need a way to ensure we don't end up with dangling pointers or corrupted iteration, so `for_each_safe` is the tell. Now I'm mentally formulating a mental search strategy... I need to find the definition, where it's used, and the accompanying synchronization primitives, so I can analyze whether this is implemented correctly. It's time to start searching.
|
| 41/2 |
2026/06/30 00:46 |
tool |
grepper |
0m
Args: map[Expression:lwq_for_each_safe PathPrefix:]
Results: map[Output:.clang-format=71=ForEachMacros:
--
.clang-format-574- - 'llist_for_each_safe'
.clang-format:575: - 'lwq_for_each_safe'
.clang-format-576- - 'map__for_each_symbol'
--
include/linux/lwq.h=69=struct llist_node *lwq_dequeue_all(struct lwq *q);
--
include/linux/lwq.h-71-/**
include/linux/lwq.h:72: * lwq_for_each_safe - iterate over detached queue allowing deletion
include/linux/lwq.h-73- * @_n: iterator variable
--
include/linux/lwq.h-81- */
include/linux/lwq.h:82:#define lwq_for_each_safe(_n, _t1, _t2, _l, _member) \
include/linux/lwq.h-83- for (_t1 = (_l); \
--
lib/lwq.c=99=static int lwq_test(void)
--
lib/lwq.c-137- l = lwq_dequeue_all(&q);
lib/lwq.c:138: printk(KERN_INFO " lwq: delete the multiples of 3 (test lwq_for_each_safe())\n");
lib/lwq.c:139: lwq_for_each_safe(t, t1, t2, &l, n) {
lib/lwq.c-140- if ((t->i % 3) == 0) {
--
net/sunrpc/svc_xprt.c=1186=static void svc_clean_up_xprts(struct svc_serv *serv, struct net *net)
--
net/sunrpc/svc_xprt.c-1195- q = lwq_dequeue_all(&pool->sp_xprts);
net/sunrpc/svc_xprt.c:1196: lwq_for_each_safe(xprt, t1, t2, &q, xpt_ready) {
net/sunrpc/svc_xprt.c-1197- if (xprt->xpt_net == net) {
]
|
| 42/2 |
2026/06/30 00:46 |
llm |
expert |
0m
Model:
Tokens:
input: 34595
output: 40
thoughts: 25
Thoughts: Here's my attempt at summarizing the thought process, tailored for an expert audience:
**Diving into the Lightweight Workqueue Implementation**
Okay, so I need to jog my memory on the specifics of the `lwq_for_each_safe` macro, specifically within the lightweight workqueue implementation. My first instinct, given my familiarity with the kernel's architecture, is to go directly to the source. Let's see... `include/linux/lwq.h` should be the most logical place to find the definition and relevant context for that particular macro, so let's start there. I'm going to look up `lwq_for_each_safe` in that header file to refresh my knowledge of the loop's structure and any subtleties of its implementation. Hopefully it's implemented inline or simply included. From there I'll be looking for relevant data structures and any interactions with the workqueue's internal mechanisms. The goal is to either recall the details, or refresh my memory.
|
| 43/2 |
2026/06/30 00:46 |
tool |
codesearch-definition-source |
0m
Error:
Args: map[ContextFile:include/linux/lwq.h Name:lwq_for_each_safe]
Results: map[SourceCode: SourceFile:]
|
| 44/2 |
2026/06/30 00:46 |
llm |
expert |
0m
Model:
Tokens:
input: 34892
output: 35
thoughts: 30
Thoughts: Okay, here's my interpretation of that thought process, from an expert's perspective:
**Diving into the Lightweight Workqueue Macro**
Right, so this is definitely a macro. I need to get a handle on what it's doing, and quickly. Forget wading through the general documentation right now; I need to see the implementation. Let's jump straight to the source. Specifically, I need to read lines 70 through 90 in `include/linux/lwq.h`. That's where the heart of this macro should be. Knowing what I already do about LWQs, that's likely where the core functionality, or at least the definition, will be located. Time to get my hands dirty and see how this thing is actually built.
|
| 45/2 |
2026/06/30 00:47 |
tool |
read-file |
0m
Args: map[File:include/linux/lwq.h FirstLine:70 LineCount:20]
Results: map[Contents: 70:
71: /**
72: * lwq_for_each_safe - iterate over detached queue allowing deletion
73: * @_n: iterator variable
74: * @_t1: temporary struct llist_node **
75: * @_t2: temporary struct llist_node *
76: * @_l: address of llist_node pointer from lwq_dequeue_all()
77: * @_member: member in _n where lwq_node is found.
78: *
79: * Iterate over members in a dequeued list. If the iterator variable
80: * is set to NULL, the iterator removes that entry from the queue.
81: */
82: #define lwq_for_each_safe(_n, _t1, _t2, _l, _member) \
83: for (_t1 = (_l); \
84: *(_t1) ? (_n = container_of(*(_t1), typeof(*(_n)), _member.node),\
85: _t2 = ((*_t1)->next), \
86: true) \
87: : false; \
88: (_n) ? (_t1 = &(_n)->_member.node.next, 0) \
89: : ((*(_t1) = (_t2)), 0))
]
|
| 46/2 |
2026/06/30 00:47 |
llm |
expert |
0m
Model:
Tokens:
input: 35503
output: 39
thoughts: 4809
Thoughts: **Analyzing a Potential NFSd Listener Hang**
Okay, here's the breakdown of my thinking. I'm focusing on a potential hang in the NFSd network listener shutdown path, specifically related to the interaction between `svc_clean_up_xprts`, `svc_close_list`, and the transport data structure.
First, I see the use of `lwq_for_each_safe` and the crucial line `xprt = NULL` within the loop. This clears a transport from the local work queue (`q`), and subsequent calls will correctly dequeue it from the list. The loop uses a safe iterator and correctly handles the removal of list elements during traversal.
The key question is the lifecycle of `xprt`: When is it in `sv_permsocks` and when is it in `pool->sp_xprts` (the work queue)? I know `svc_delete_xprt` removes it from `sv_permsocks`. I'm concerned about a race condition where a transport might be in `sv_permsocks`, have `XPT_BUSY` set (indicating an active operation on it), but *not* be in `pool->sp_xprts`. This is the crux of the issue.
`svc_xprt_enqueue` is the function responsible for putting the transport on the `sp_xprts` queue. It first checks and sets `XPT_BUSY`. Critically, the enqueue happens *after* `XPT_BUSY` is set atomically, thus preventing double enqueue. If a concurrent call to `svc_close_list` sets `XPT_CLOSE` *before* `svc_xprt_enqueue` gets a chance to run, the `svc_xprt_enqueue` will see the BUSY flag and return. This, on its own, seems safe.
Now, I consider concurrency between `svc_xprt_enqueue` and `svc_clean_up_xprts`. `svc_clean_up_xprts` calls `lwq_dequeue_all`, which should atomically dequeue all items on the list. I have to think about ordering again here. If a transport is enqueued, and `svc_clean_up_xprts` is called concurrently, it will dequeue and close them. This seems correct, if there's an `XPT_CLOSE` flag set. What if a thread is *actively processing* the transport? Then `XPT_BUSY` is set, and the transport is not in the queue. `svc_close_list` is called and sees the BUSY flag, it returns immediately and *doesn't* enqueue it. This is okay, the processing thread will eventually finish and call `svc_xprt_received`, which clears `XPT_BUSY`, sets the CLOSE flag and enqueues the transport.
However, the code in `nfsd_nl_listener_set_doit` seems to invalidate that conclusion. It explicitly checks `serv->sv_nrthreads`. If the number of threads is zero, then no thread could have an active transport. If no thread is active, and if the transport isn't in `sp_xprts`, then it's in a problematic state! A transport could be in `pool->sp_xprts` but not be deleted because it is assigned to the wrong pool, but `svc_pool_for_cpu` should prevent this. The code enqueues the sockets into the correct pool.
Let's trace: the transport could be enqueued, and `svc_clean_up_xprts` might fail to delete it, but this seems unlikely. The `lwq_enqueue` and `lwq_dequeue_all` functions are atomic. Now the scenario of `svc_xprt_enqueue` being called twice. The second call should return immediately due to the `XPT_BUSY` flag. The enqueuing is guarded by the busy flag.
What about a race condition? If `svc_clean_up_xprts` dequeues the item, but then its `xpt_net != net`, so the function ignores the xprt, but enqueues it back to the work queue, `XPT_BUSY` remains set, as designed. `svc_close_list` with a different net will ignore it.
Okay, let's look at `svc_delete_xprt`. I see it calls `list_del_init`. However, `test_and_set_bit(XPT_DEAD, &xprt->xpt_flags)` might cause `svc_delete_xprt` to return immediately *without* removing it. This
|
| 47/2 |
2026/06/30 00:47 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/sunrpc/svc_xprt.c Name:svc_recv]
Results: map[SourceCode: 904: /**
905: * svc_recv - Receive and process the next request on any transport
906: * @rqstp: an idle RPC service thread
907: * @timeo: timeout (in jiffies) (0 means infinite timeout)
908: *
909: * This code is carefully organised not to touch any cachelines in
910: * the shared svc_serv structure, only cachelines in the local
911: * svc_pool.
912: *
913: * If the timeout is 0, then the sleep will never time out.
914: *
915: * Returns -ETIMEDOUT if idle for an extended period
916: * -EBUSY if there is more work to do than available threads
917: * 0 otherwise.
918: */
919: int svc_recv(struct svc_rqst *rqstp, long timeo)
920: {
921: struct svc_pool *pool = rqstp->rq_pool;
922: bool did_timeout;
923: int ret = 0;
924:
925: if (!svc_alloc_arg(rqstp))
926: return ret;
927:
928: did_timeout = svc_thread_wait_for_work(rqstp, timeo);
929:
930: if (did_timeout && svc_thread_should_sleep(rqstp) &&
931: pool->sp_nrthrmin && pool->sp_nrthreads > pool->sp_nrthrmin)
932: ret = -ETIMEDOUT;
933:
934: clear_bit(SP_TASK_PENDING, &pool->sp_flags);
935:
936: if (svc_thread_should_stop(rqstp)) {
937: svc_thread_wake_next(rqstp);
938: return ret;
939: }
940:
941: rqstp->rq_xprt = svc_xprt_dequeue(pool);
942: if (rqstp->rq_xprt) {
943: struct svc_xprt *xprt = rqstp->rq_xprt;
944:
945: svc_thread_wake_next(rqstp);
946: /* Normally we will wait up to 5 seconds for any required
947: * cache information to be provided. When there are no
948: * idle threads, we reduce the wait time.
949: */
950: if (pool->sp_idle_threads.first) {
951: rqstp->rq_chandle.thread_wait = 5 * HZ;
952: } else {
953: rqstp->rq_chandle.thread_wait = 1 * HZ;
954: /*
955: * No idle threads: signal -EBUSY so the caller
956: * can consider spawning another thread. Use
957: * SP_TASK_STARTING to limit this signal to one
958: * thread at a time; the caller clears this flag
959: * after starting a new thread.
960: */
961: if (!did_timeout && timeo &&
962: !test_and_set_bit(SP_TASK_STARTING,
963: &pool->sp_flags))
964: ret = -EBUSY;
965: }
966:
967: trace_svc_xprt_dequeue(rqstp);
968: svc_handle_xprt(rqstp, xprt);
969: }
970:
971: #if defined(CONFIG_SUNRPC_BACKCHANNEL)
972: if (svc_is_backchannel(rqstp)) {
973: struct svc_serv *serv = rqstp->rq_server;
974: struct rpc_rqst *req;
975:
976: req = lwq_dequeue(&serv->sv_cb_list,
977: struct rpc_rqst, rq_bc_list);
978: if (req) {
979: svc_thread_wake_next(rqstp);
980: svc_process_bc(req, rqstp);
981: }
982: }
983: #endif
984: return ret;
985: }
SourceFile:net/sunrpc/svc_xprt.c]
|
| 48/2 |
2026/06/30 00:47 |
llm |
expert |
0m
Model:
Tokens:
input: 42678
output: 60
thoughts: 1675
Thoughts: **Analyzing Transport Destruction and Busy States**
Okay, let's break this down systematically. My initial understanding is that if `svc_thread_should_stop` returns, the thread bails, but *doesn't* dequeue or process a transport, which is key. The normal flow involves `svc_handle_xprt` processing and eventually calling either `svc_xprt_received` or `svc_delete_xprt`. The thread shouldn't exit with a busy transport.
Hmm, but what if `svc_handle_xprt` calls `svc_delete_xprt` and somehow leaves `XPT_BUSY` set? The code shows that if `XPT_CLOSE` is set and `XPT_KILL_TEMP` too, it calls the kill function, then calls `svc_delete_xprt` *but* can leave `XPT_BUSY` set. However, `svc_delete_xprt` *should* remove it from `sv_permsocks`, right? The code confirms that with `list_del_init`. So, the transport shouldn't be in `sv_permsocks` anymore. Then `svc_close_list` wouldn't find it. Good.
The critical question is, are there other ways a transport could be in `sv_permsocks` with `XPT_BUSY`? What about `svc_xprt_enqueue` failing after setting `XPT_BUSY`? It can't fail, because it uses a linked list, so enqueue failures aren't an issue.
Then, what about a transport being created but never added to `sv_permsocks` via `svc_add_new_perm_xprt`? If it's not added, it's not in the list. Okay.
What if `svc_xprt_init` sets `XPT_BUSY`, and something else adds it to `sv_permsocks`? `svc_add_new_perm_xprt` clears `XPT_TEMP`, adds to `sv_permsocks`, and then calls `svc_xprt_received(new)`. `svc_xprt_received` clears `XPT_BUSY`. So it should be cleared.
Could there be a race? If `svc_xprt_received` clears `XPT_BUSY`, but then `svc_xprt_enqueue` is called concurrently? `svc_xprt_enqueue` would set `XPT_BUSY` and enqueue it. It's fine.
Okay, let's look at `svc_xprt_destroy_all`. Could a transport be in `pool->sp_xprts` but not be deleted in `svc_clean_up_xprts`? I need to review `svc_clean_up_xprts`. The code dequeues ALL elements from `pool->sp_xprts`. It iterates through them. If `xprt->xpt_net == net`, it calls `svc_delete_xprt(xprt)` and *also* sets the pointer to NULL. After all that it enqueues the remaining elements.
But wait, what if `svc_delete_xprt` doesn't *actually* remove it from `sv_permsocks`? It calls `list_del_init`, but there's a crucial check with `XPT_DEAD`. If `XPT_DEAD` is already set, it returns immediately! So the transport *isn't* removed from `sv_permsocks`. I now see the pattern.
If `XPT_DEAD` is already set, another `svc_delete_xprt` already ran. Because `XPT_DEAD` is only set in `svc_delete_xprt`, a previous call MUST have removed the transport from `sv_permsocks`. The first caller sets `XPT_DEAD` and does `list_del_init`. A subsequent call finds `XPT_DEAD` set and returns. So it WILL be removed. Got it.
Okay, now the real race condition scenario: could `svc_delete_xprt` be called, set `XPT_DEAD`, but BEFORE taking the lock and removing from `sv_permsocks`, `svc_close_list` *takes* the lock and iterates over the list? Bingo!
`svc_close_list` finds the transport, sets `XPT_CLOSE`, and calls `svc_xprt_enqueue`. This sets `XPT_BUSY` (if not already set) and enqueues.
BUT, let's see, `svc_xprt_destroy_all` is called from `n
|
| 49/2 |
2026/06/30 00:47 |
tool |
codesearch-find-references |
0m
Args: map[ContextFile:net/sunrpc/svc_xprt.c IncludeSnippetLines:2 Name:svc_delete_xprt SourceTreePrefix:net/sunrpc]
Results: map[References:[map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:svc_clean_up_xprts SourceFile:net/sunrpc/svc_xprt.c SourceLine:1199 SourceSnippet:1197: if (xprt->xpt_net == net) {
1198: set_bit(XPT_CLOSE, &xprt->xpt_flags);
1199: svc_delete_xprt(xprt);
1200: xprt = NULL;
1201: }
] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:svc_handle_xprt SourceFile:net/sunrpc/svc_xprt.c SourceLine:840 SourceSnippet: 838: if (test_and_clear_bit(XPT_KILL_TEMP, &xprt->xpt_flags))
839: xprt->xpt_ops->xpo_kill_temp_xprt(xprt);
840: svc_delete_xprt(xprt);
841: /* Leave XPT_BUSY set on the dead xprt: */
842: goto out;
] map[ReferenceKind:calls ReferencingEntityKind:function ReferencingEntityName:svc_xprt_close SourceFile:net/sunrpc/svc_xprt.c SourceLine:1165 SourceSnippet:1163: * it ourself:
1164: */
1165: svc_delete_xprt(xprt);
1166: }
]] TruncatedOutput:false]
|
| 50/2 |
2026/06/30 00:47 |
llm |
expert |
0m
Model:
Tokens:
input: 45899
output: 49
thoughts: 5380
Thoughts: **Analyzing a Potential NFS Server Deadlock**
Alright, let's break this down. My initial thought process revolves around `svc_xprt_close` and its interaction with `svc_delete_xprt`. I see that `svc_xprt_close` is designed to handle closing a transport, with `svc_delete_xprt` doing the actual removal. The important part is the `XPT_BUSY` flag. If a transport is busy, the close is deferred. I need to figure out the calling context of `svc_xprt_close`.
My mind immediately jumps to `svc_xprt_destroy_all` but that calls `svc_close_list`, which is a key observation. Now I see that `svc_close_list` *enqueues* the transport using `svc_xprt_enqueue`. Here's where it gets interesting: `svc_xprt_enqueue` has a return if `XPT_BUSY` is set! If it returns, the transport is NOT enqueued. `svc_clean_up_xprts` will not find it!
This leads me to a critical point: If a transport is busy (`XPT_BUSY` is set) but not enqueued to the clean up list, `svc_clean_up_xprts` will miss it, and `svc_close_list` will encounter it again, leading to an infinite loop, or so I believe.
My next step is to find out how a transport could possibly have its `XPT_BUSY` flag set but not be in the clean-up list. Digging deeper I see `nfsd_nl_listener_set_doit` which manages transports, and I note that it moves existing transports to a `permsocks` list, checks the network sockets, and then moves some of them *back* to `sv_permsocks`, and ultimately calls `svc_xprt_destroy_all`. But what's really happening during the transition? I must check the flags and conditions.
Aha! `nfsd_nl_listener_set_doit` initially creates a bunch of listeners and puts them in `permsocks`, and then moves some to the main server list and potentially destroys the rest. My concern is, what if `svc_xprt_create_from_sa` fails partway through creating the new listener, leaving it in a weird state? But then I remember `svc_xprt_create_from_sa` calls `svc_add_new_perm_xprt` which clears `XPT_BUSY`. This does not seem likely.
Now, I consider an asynchronous context, perhaps a callback or timer. Could `svc_xprt_enqueue` be triggered by the network stack, such as via `svc_udp_data_ready` or `svc_tcp_data_ready`? Yes! Now, it makes sense: a packet arrives, `svc_xprt_enqueue` is called, and sets `XPT_BUSY`. This seems normal: a network event.
Now, if `svc_xprt_enqueue` sets `XPT_BUSY` but `lwq_enqueue` is not called, there is a chance of this happening. But then again, this must happen within the same function calls and therefore there can be no blocking.
Alright, so `svc_recv` will dequeue it, call `svc_handle_xprt`, which might clear `XPT_BUSY` or delete the transport. But, `nfsd_nl_listener_set_doit` checks if there are threads and only calls `svc_xprt_destroy_all` if `sv_nrthreads` is 0. If `serv->sv_nrthreads` is 0, no threads should be active, so `svc_recv` can't be in the middle of processing. I am now confused, where am I going wrong?
I revisit `svc_xprt_close`. If `svc_xprt_close` is called and `XPT_BUSY` is already set, it simply returns. Who calls `svc_xprt_close`? `svc_close_list` does NOT call `svc_xprt_close`. `svc_close_list` sets `XPT_CLOSE` and calls `svc_xprt_enqueue`, which means we return and therefore avoid enqueuing.
What I am missing is `svc_xprt_ready` which is called by `svc_xprt_enqueue`. If the transport is NOT `svc_xprt_ready` it returns WITHOUT setting `XPT_BUSY`. And if `svc_xpr
|
| 51/2 |
2026/06/30 00:48 |
tool |
git-log |
0m
Error:
Args: map[Count:1 PathPrefix:fs/nfsd/nfsctl.c SymbolName:nfsd_nl_listener_set_doit]
Results:
|
| 52/2 |
2026/06/30 00:48 |
llm |
expert |
0m
Model:
Tokens:
input: 52375
output: 49
thoughts: 8
Thoughts: Okay, here's the summary, rendered as a first-person thought process assuming the user is an expert.
**The SourcePath Strategy**
Right, so I'm thinking about the approach for this. Hmm, the initial setup is in place, I believe. Given the problem at hand, itβs clear I should leverage SourcePath for the solution here. Itβs the obvious choice, really, considering the specific constraints and the nature of the data involved. No need to overcomplicate things; SourcePath provides the directness and efficiency I require. Let's make this work.
|
| 53/2 |
2026/06/30 00:48 |
tool |
git-log |
0m
Args: map[Count:1 SourcePath:fs/nfsd/nfsctl.c SymbolName:nfsd_nl_listener_set_doit]
Results: map[Output:92978c83bb4e nfsd: Fix cred ref leak in nfsd_nl_listener_set_doit().
]
|
| 54/2 |
2026/06/30 00:48 |
llm |
expert |
0m
Model:
Tokens:
input: 52603
output: 43
thoughts: 1079
Thoughts: **Debugging a Potential NFSd Hang**
Alright, let's dive back into this `nfsd_nl_listener_set_doit` function and see if we can finally get to the bottom of this hang. I see we're holding `nfsd_mutex` and then calling `nfsd_create_serv`. If that fails, we return early. But the code path I'm interested in is where everything seems to work, and we end up with this mutex held indefinitely.
If `svc_xprt_destroy_all` is looping, it's very likely sleeping with `msleep`. We know the hung task timeout is 143 seconds. The core issue is, *why* is `svc_close_list` not returning 0? It looks like we've got transports stuck in `sv_permsocks` that aren't being cleaned up by `svc_clean_up_xprts`. Why aren't they being deleted? Because they aren't in `pool->sp_xprts`. This means `svc_xprt_enqueue` never enqueued them.
And why did `svc_xprt_enqueue` not enqueue them? `svc_xprt_ready(xprt)` returned `false`. So, *why* is `svc_xprt_ready` returning `false`? Because the `XPT_BUSY` flag was ALREADY set! How can that be? The transport wasn't in `pool->sp_xprts`.
This is the critical question. Let's trace the lifecycle of a transport.
1. `svc_xprt_create_from_sa` -> `_svc_xprt_create` -> `svc_xprt_init`. `svc_xprt_init` *sets* `XPT_BUSY`. This is the first place we see it.
2. `_svc_xprt_create` calls `xcl->xcl_ops->xpo_create`, for example, `svc_tcp_create`, where a socket is created and callbacks are set up.
3. `_svc_xprt_create` then calls `svc_add_new_perm_xprt`. This function adds the transport to `sv_permsocks` *and* calls `svc_xprt_received`.
4. `svc_xprt_received` *clears* `XPT_BUSY`. If `XPT_CLOSE` is set, it calls `svc_xprt_enqueue`.
Okay, what are the failure paths here? What if `xcl->xcl_ops->xpo_create` FAILS? If it fails, it returns an error pointer, `ERR_PTR`, and `_svc_xprt_create` returns that error. The transport is then freed and never makes it into `sv_permsocks`, and thus, isn't part of our problem. So, not this path.
What if `xpo_create` succeeds, but something interrupts the process after `svc_add_new_perm_xprt` is called? The problem is `svc_add_new_perm_xprt` CLEARS `XPT_BUSY` as part of its operations, so this should be fine.
Aha! What if a network packet arrives *before* `svc_add_new_perm_xprt` is called? The socket callbacks are setup in `xpo_create`. If a packet arrives, the callback (like `svc_tcp_data_ready`) is called. That callback calls `svc_xprt_enqueue`, which, crucially, calls `svc_xprt_ready`. Since `XPT_BUSY` is STILL SET (because `svc_add_new_perm_xprt` hasn't cleared it yet), `svc_xprt_ready` returns `false`, and `svc_xprt_enqueue` *does nothing*. This makes sense! `svc_add_new_perm_xprt` is going to call `svc_xprt_received` which is supposed to clear `XPT_BUSY` and enqueue any pending transport calls. But what *does* it check? It checks if `XPT_CLOSE` is set, calls `svc_xprt_enqueue`. Oh, wait! If data has arrived `XPT_DATA` will be set. But does `svc_xprt_received` check it?
Let me check `svc_xprt_received`.
|
| 55/2 |
2026/06/30 00:48 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/sunrpc/svc_xprt.c Name:svc_xprt_received]
Results: map[SourceCode: 214: /**
215: * svc_xprt_received - start next receiver thread
216: * @xprt: controlling transport
217: *
218: * The caller must hold the XPT_BUSY bit and must
219: * not thereafter touch transport data.
220: *
221: * Note: XPT_DATA only gets cleared when a read-attempt finds no (or
222: * insufficient) data.
223: */
224: void svc_xprt_received(struct svc_xprt *xprt)
225: {
226: if (!test_bit(XPT_BUSY, &xprt->xpt_flags)) {
227: WARN_ONCE(1, "xprt=0x%p already busy!", xprt);
228: return;
229: }
230:
231: /* As soon as we clear busy, the xprt could be closed and
232: * 'put', so we need a reference to call svc_xprt_enqueue with:
233: */
234: svc_xprt_get(xprt);
235: smp_mb__before_atomic();
236: clear_bit(XPT_BUSY, &xprt->xpt_flags);
237:
238: /*
239: * Skip the enqueue when no actionable flags are set.
240: * Each producer both sets its flag (XPT_DATA, XPT_CLOSE,
241: * etc.) and calls svc_xprt_enqueue(); if a set_bit races
242: * with this check, the producer's own enqueue observes
243: * !XPT_BUSY and dispatches the transport.
244: */
245: if (READ_ONCE(xprt->xpt_flags) &
246: (BIT(XPT_CONN) | BIT(XPT_CLOSE) | BIT(XPT_HANDSHAKE) |
247: BIT(XPT_DATA) | BIT(XPT_DEFERRED)))
248: svc_xprt_enqueue(xprt);
249:
250: svc_xprt_put(xprt);
251: }
SourceFile:net/sunrpc/svc_xprt.c]
|
| 56/2 |
2026/06/30 00:48 |
llm |
expert |
1m
Model:
Tokens:
input: 55403
output: 34
thoughts: 1477
Thoughts: **Analyzing the Transport Lifecycle**
Okay, so `svc_xprt_received` *does* check `XPT_DATA` and enqueues using `svc_xprt_enqueue`. That part seems sound.
But, a thought keeps nagging: what if `svc_xprt_enqueue` sets `XPT_BUSY` and enqueues to the `pool->sp_xprts`, but `svc_clean_up_xprts` *somehow* misses it? We know `xprt->xpt_net == net` for our cases. Could `svc_pool_for_cpu` return a pool not checked by `svc_clean_up_xprts`? No, because `svc_pool_for_cpu` returns one of the server's pools, which `svc_clean_up_xprts` iterates through.
Right, `svc_clean_up_xprts` *does* call `svc_delete_xprt` after dequeuing, which should remove it from the list. `svc_delete_xprt` then calls `list_del_init` on `xpt_list`. But wait! `svc_close_list` iterates through `sv_permsocks` using `list_for_each_entry`.
If `svc_close_list` sets `XPT_CLOSE` and *then* calls `svc_xprt_enqueue`, which sets `XPT_BUSY` and enqueues, and then unlocks the lock, and then `svc_clean_up_xprts` is called... it should work perfectly. `svc_clean_up_xprts` dequeues, calls `svc_delete_xprt` and the list is cleaned. So, why the hang?
Is there *any* case where `svc_xprt_enqueue` *doesn't* enqueue? Yes, if `!svc_xprt_ready(xprt)`. When does `svc_xprt_ready` return false? If `XPT_BUSY` is set, or if `XPT_CONN`, `XPT_CLOSE`, `XPT_HANDSHAKE` are *not* set, AND `XPT_DATA`, `XPT_DEFERRED` are *not* set. But `svc_close_list` just *set* `XPT_CLOSE`! So unless `XPT_BUSY` is already set, `svc_xprt_ready` *should* return true.
The *only* way `svc_xprt_enqueue` does *not* enqueue it is if `XPT_BUSY` is already set! Where would `XPT_BUSY` *already* be set?
1. `svc_xprt_init` (but it's cleared by `svc_add_new_perm_xprt`).
2. `svc_xprt_enqueue` (called by *someone else*).
If `svc_xprt_enqueue` was called by someone else, it *must* have enqueued it to `pool->sp_xprts`. If it's in `pool->sp_xprts`, `svc_clean_up_xprts` *will* find it and delete it. Wait! What if `svc_clean_up_xprts` DOES NOT find it in `pool->sp_xprts`?
How could it not be there? If it was dequeued by `svc_recv`. But `sv_nrthreads` is 0, so no threads are running `svc_recv`.
Wait, what if `sv_nrthreads` WAS 0, but a thread WAS running, dequeued it, and then EXITED? If a thread exits, it calls `svc_exit_thread`. Does it put the transport back?
Let's check `svc_recv`. If a thread dequeues it, it *always* calls `svc_handle_xprt`. `svc_handle_xprt` *always* calls `svc_xprt_received` or `svc_delete_xprt`. So, it *always* clears `XPT_BUSY` or deletes it. So a thread *cannot* exit with `XPT_BUSY` set!
Wait! What if `svc_handle_xprt` calls `svc_xprt_received`, which clears `XPT_BUSY`, and then the thread exits. Now `XPT_BUSY` is 0. So `svc_close_list` *will* enqueue it!
Is there any other
|
| 57/2 |
2026/06/30 00:50 |
tool |
grepper |
0m
Args: map[Expression:lwq_dequeue.*sp_xprts PathPrefix:net/sunrpc]
Results: map[Output:net/sunrpc/svc_xprt.c=535=static struct svc_xprt *svc_xprt_dequeue(struct svc_pool *pool)
--
net/sunrpc/svc_xprt.c-538-
net/sunrpc/svc_xprt.c:539: xprt = lwq_dequeue(&pool->sp_xprts, struct svc_xprt, xpt_ready);
net/sunrpc/svc_xprt.c-540- if (xprt)
--
net/sunrpc/svc_xprt.c=1186=static void svc_clean_up_xprts(struct svc_serv *serv, struct net *net)
--
net/sunrpc/svc_xprt.c-1194-
net/sunrpc/svc_xprt.c:1195: q = lwq_dequeue_all(&pool->sp_xprts);
net/sunrpc/svc_xprt.c-1196- lwq_for_each_safe(xprt, t1, t2, &q, xpt_ready) {
]
|
| 58/2 |
2026/06/30 00:50 |
llm |
expert |
0m
Model:
Tokens:
input: 58236
output: 43
thoughts: 776
Thoughts: **Analyzing Transport Dequeueing and Destruction**
Okay, let's break this down. My initial observation is that only `svc_xprt_dequeue` and `svc_clean_up_xprts` are involved in dequeuing from `sp_xprts`. `svc_xprt_dequeue` is called by `svc_recv`, so only those two functions have the power to do this.
Now, I'm thinking about the enqueueing process. If `svc_xprt_enqueue` is called and sets `XPT_BUSY` before enqueuing, and `svc_clean_up_xprts` later dequeues it, what scenarios exist? `svc_clean_up_xprts` checks `xprt->xpt_net == net`. If it *doesn't* match, the transport is re-enqueued. But, what if the network is the same, *and* `svc_delete_xprt` doesn't remove it from `sv_permsocks`? I remember we checked that: `svc_delete_xprt` calls `list_del_init(&xprt->xpt_list)`.
Wait, what if `svc_delete_xprt` is called, but `XPT_DEAD` is *already* set? If `XPT_DEAD` is already set, that means `svc_delete_xprt` was already called, meaning it was already removed from `sv_permsocks`, it CANNOT be there.
Hmm... is it even possible for `list_del_init` to be called and for the transport to *still* be in `sv_permsocks`? No, that can't happen, `list_del_init` does the removal.
Aha! Let's revisit `nfsd_nl_listener_set_doit`. If a transport is moved to `sv_permsocks`, it *is* in `sv_permsocks`. I now see that `svc_xprt_destroy_all` is called after this. That then calls `svc_close_list`, which sets `XPT_CLOSE` and calls `svc_xprt_enqueue`. Subsequently, `svc_clean_up_xprts` dequeues it and then calls `svc_delete_xprt`. Crucially, `svc_delete_xprt` sets `XPT_DEAD` and calls `list_del_init(&xprt->xpt_list)`. So, it *is* removed from `sv_permsocks`.
One last thing, what if `svc_delete_xprt` is called, but it somehow *doesn't* call `list_del_init`? I'd better double-check `svc_delete_xprt` again, just to be sure.
|
| 59/2 |
2026/06/30 00:50 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/sunrpc/svc_xprt.c Name:svc_delete_xprt]
Results: map[SourceCode:1104: /*
1105: * Remove a dead transport
1106: */
1107: static void svc_delete_xprt(struct svc_xprt *xprt)
1108: {
1109: struct svc_serv *serv = xprt->xpt_server;
1110: struct svc_deferred_req *dr;
1111:
1112: /* unregister with rpcbind for when transport type is TCP or UDP.
1113: */
1114: if (test_bit(XPT_RPCB_UNREG, &xprt->xpt_flags)) {
1115: struct svc_sock *svsk = container_of(xprt, struct svc_sock,
1116: sk_xprt);
1117: struct socket *sock = svsk->sk_sock;
1118:
1119: if (svc_register(serv, xprt->xpt_net, sock->sk->sk_family,
1120: sock->sk->sk_protocol, 0) < 0)
1121: pr_warn("failed to unregister %s with rpcbind\n",
1122: xprt->xpt_class->xcl_name);
1123: }
1124:
1125: if (test_and_set_bit(XPT_DEAD, &xprt->xpt_flags))
1126: return;
1127:
1128: trace_svc_xprt_detach(xprt);
1129: xprt->xpt_ops->xpo_detach(xprt);
1130: if (xprt->xpt_bc_xprt)
1131: xprt->xpt_bc_xprt->ops->close(xprt->xpt_bc_xprt);
1132:
1133: spin_lock_bh(&serv->sv_lock);
1134: list_del_init(&xprt->xpt_list);
1135: if (test_bit(XPT_TEMP, &xprt->xpt_flags) &&
1136: !test_bit(XPT_PEER_VALID, &xprt->xpt_flags))
1137: serv->sv_tmpcnt--;
1138: spin_unlock_bh(&serv->sv_lock);
1139:
1140: while ((dr = svc_deferred_dequeue(xprt)) != NULL)
1141: free_deferred(xprt, dr);
1142:
1143: call_xpt_users(xprt);
1144: svc_xprt_put(xprt);
1145: }
SourceFile:net/sunrpc/svc_xprt.c]
|
| 60/2 |
2026/06/30 00:50 |
llm |
expert |
0m
Model:
Tokens:
input: 60463
output: 39
thoughts: 146
Thoughts: **Investigating Potential Blocking in `svc_register`**
Okay, here's what's running through my head. I'm wondering about a potential blocking issue within `svc_register`. Specifically, my concern centers around the fact that `svc_register` likely calls `rpcb_v4_register` or a similar function, which almost certainly involves making an RPC call. And that, of course, could lead to blocking. RPC calls are notorious for introducing potential delays due to network latency, server availability, etc.
But hang on⦠I need to consider the context. I remember that `svc_xprt_destroy_all` is called while holding `nfsd_mutex`. If `svc_register` were to block indefinitely, that would be a serious problem and likely lead to a deadlock. However, if it were blocking, it would simply sleep, not loop forever.
My next thought is about the hung task timeout. That's currently set at 143 seconds. If `svc_register` *did* block for that long, the system would detect the hung task and trigger a warning.
Wait a second, let's go back and be sure: Does `svc_register` make an RPC call? I think I need to trace through the code. I need to dive into `svc_register` itself to be completely certain. I need to be sure that I am understanding all aspects of this function.
|
| 61/2 |
2026/06/30 00:50 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/sunrpc/svc_xprt.c Name:svc_register]
Results: map[SourceCode:1214: /**
1215: * svc_register - register an RPC service with the local portmapper
1216: * @serv: svc_serv struct for the service to register
1217: * @net: net namespace for the service to register
1218: * @family: protocol family of service's listener socket
1219: * @proto: transport protocol number to advertise
1220: * @port: port to advertise
1221: *
1222: * Service is registered for any address in the passed-in protocol family
1223: */
1224: int svc_register(const struct svc_serv *serv, struct net *net,
1225: const int family, const unsigned short proto,
1226: const unsigned short port)
1227: {
1228: unsigned int p, i;
1229: int error = 0;
1230:
1231: WARN_ON_ONCE(proto == 0 && port == 0);
1232: if (proto == 0 && port == 0)
1233: return -EINVAL;
1234:
1235: for (p = 0; p < serv->sv_nprogs; p++) {
1236: struct svc_program *progp = &serv->sv_programs[p];
1237:
1238: for (i = 0; i < progp->pg_nvers; i++) {
1239:
1240: error = progp->pg_rpcbind_set(net, progp, i,
1241: family, proto, port);
1242: if (error < 0) {
1243: printk(KERN_WARNING "svc: failed to register "
1244: "%sv%u RPC service (errno %d).\n",
1245: progp->pg_name, i, -error);
1246: break;
1247: }
1248: }
1249: }
1250:
1251: return error;
1252: }
SourceFile:net/sunrpc/svc.c]
|
| 62/2 |
2026/06/30 00:50 |
llm |
expert |
0m
Model:
Tokens:
input: 61554
output: 31
thoughts: 31
Thoughts: Okay, here's my summary, presented as a stream of thought:
**Checking RPC Binding Methods for NFS Integration**
Alright, I need to look into how we're handling RPC binding in this context. Let me make sure I'm using the right configuration method. For PostgreSQL, I'd typically be looking at something like `pg_rpcbind_set`, or something similar. But this is NFS, so it's a different beast. Right, for NFS, it's likely a similar concept, probably named `nfsd_rpcbind_set`, or something along those lines. I need to track down the correct documentation or configuration option for this specific NFS implementation, to ensure RPC is being bound correctly. Itβs important to find the right variable and make sure itβs configured the way I need it to be.
|
| 63/2 |
2026/06/30 00:50 |
tool |
grepper |
0m
Args: map[Expression:pg_rpcbind_set PathPrefix:fs/nfsd]
Results: map[Output:fs/nfsd/nfssvc.c=107=struct svc_program nfsd_programs[] = {
--
fs/nfsd/nfssvc.c-115- .pg_init_request = nfsd_init_request,
fs/nfsd/nfssvc.c:116: .pg_rpcbind_set = nfsd_rpcbind_set,
fs/nfsd/nfssvc.c-117- },
--
fs/nfsd/nfssvc.c-126- .pg_init_request = nfsd_acl_init_request,
fs/nfsd/nfssvc.c:127: .pg_rpcbind_set = nfsd_acl_rpcbind_set,
fs/nfsd/nfssvc.c-128- },
--
fs/nfsd/nfssvc.c-138- .pg_init_request = svc_generic_init_request,
fs/nfsd/nfssvc.c:139: .pg_rpcbind_set = svc_generic_rpcbind_set,
fs/nfsd/nfssvc.c-140- }
]
|
| 64/2 |
2026/06/30 00:50 |
llm |
expert |
0m
Model:
Tokens:
input: 62110
output: 43
thoughts: 14
Thoughts: Okay, here's my take on those thoughts, tailored for an expert audience:
**Analyzing the `nfsd_rpcbind_set` Function Call**
Alright, let's dive into this. My initial instinct is to go straight to `nfsd_rpcbind_set`. I need to figure out what's happening there. I'm assuming we're dealing with NFS and rpcbind, so my immediate questions are centered around how the NFS server is interacting with the rpcbind daemon. Is this a registration? Deregistration? A binding update? The function name itself suggests some kind of setup or configuration related to rpcbind, but the specifics are where the devil lives. I'll need to look into how that function interacts with the kernel's NFS daemon and the rpcbind infrastructure. Is it a user-space call, a kernel call, or something else entirely? What data structures are involved? What security implications are in play? Time to get to work.
|
| 65/2 |
2026/06/30 00:50 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/nfsd/nfssvc.c Name:nfsd_rpcbind_set]
Results: map[SourceCode: 838: static int
839: nfsd_rpcbind_set(struct net *net, const struct svc_program *progp,
840: u32 version, int family, unsigned short proto,
841: unsigned short port)
842: {
843: if (!nfsd_vers(net_generic(net, nfsd_net_id), version, NFSD_TEST))
844: return 0;
845: return svc_generic_rpcbind_set(net, progp, version, family,
846: proto, port);
847: }
SourceFile:fs/nfsd/nfssvc.c]
|
| 66/2 |
2026/06/30 00:50 |
llm |
expert |
0m
Model:
Tokens:
input: 62579
output: 43
thoughts: 14
Thoughts: Okay, let's dive into this. Here's my thought process on what we're looking at, summarized from that prompt:
**Analyzing `svc_generic_rpcbind_set`**
Alright, time to get to work. First, I need to understand what we're dealing with. The prompt has just given me `svc_generic_rpcbind_set`. I need to figure out how this function fits into the bigger picture. I'm immediately thinking, "What exactly is this? What is its purpose in the system?" I'm assuming it's related to the `rpcbind` process, which, based on the function name, is probably the case, but I have to verify. The "set" part strongly suggests that it's related to configuring or registering something. I need to understand its parameters. It's likely involved in setting up or modifying the way a service is exposed through the network. What kind of data is it operating on? What's its interaction with the broader RPC infrastructure? I need to look it up, read the documentation, examine its source code and usage patterns, and start connecting the dots to get a thorough understanding.
|
| 67/2 |
2026/06/30 00:50 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/nfsd/nfssvc.c Name:svc_generic_rpcbind_set]
Results: map[SourceCode:1182: int svc_generic_rpcbind_set(struct net *net,
1183: const struct svc_program *progp,
1184: u32 version, int family,
1185: unsigned short proto,
1186: unsigned short port)
1187: {
1188: const struct svc_version *vers = progp->pg_vers[version];
1189: int error;
1190:
1191: if (vers == NULL)
1192: return 0;
1193:
1194: if (vers->vs_hidden) {
1195: trace_svc_noregister(progp->pg_name, version, proto,
1196: port, family, 0);
1197: return 0;
1198: }
1199:
1200: /*
1201: * Don't register a UDP port if we need congestion
1202: * control.
1203: */
1204: if (vers->vs_need_cong_ctrl && proto == IPPROTO_UDP)
1205: return 0;
1206:
1207: error = svc_rpcbind_set_version(net, progp, version,
1208: family, proto, port);
1209:
1210: return (vers->vs_rpcb_optnl) ? 0 : error;
1211: }
SourceFile:net/sunrpc/svc.c]
|
| 68/2 |
2026/06/30 00:50 |
llm |
expert |
0m
Model:
Tokens:
input: 63321
output: 40
thoughts: 14
Thoughts: Okay, here's my take on those thoughts, tailored for an expert audience:
**Analyzing `svc_rpcbind_set_version`**
Right, let's dive into this. I'm thinking, "Okay, `svc_rpcbind_set_version`... what's the context here?" Immediately, I'm considering its role within the broader RPC ecosystem. I'm recalling the importance of versioning in distributed systems β maintaining compatibility and allowing for graceful upgrades. I'm mentally parsing the function name itself. The "svc_" prefix typically signifies a server-side service function, the "rpcbind" component strongly suggests interaction with the portmapper or similar service registry, and "set_version" points toward the core function of declaring or modifying the RPC version being advertised or supported.
My primary concern right now is how *robust* is the handling of version conflicts or downgrades? Am I potentially opening any security vulnerabilities by allowing a client to specify an outdated, potentially compromised, version? And, what about interoperability? Does this function play nice with various RPC implementations or protocols? Specifically, I'm wondering if there are any subtle race conditions or concurrent access issues involved in changing the version. We all know how insidious those can be.
Further, I'm thinking about the implications for security. Is there proper validation of input versions? Are there any potential buffer overflows or format string vulnerabilities lurking within the implementation of this function? Am I sure it properly handles the case where the requested version is higher than the server supports or unavailable? These are all burning questions I'd be running through in my head. Ultimately, I'm attempting to deconstruct the likely function's usage, its limitations, and to assess whether it poses any immediate threats.
|
| 69/2 |
2026/06/30 00:50 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/sunrpc/svc.c Name:svc_rpcbind_set_version]
Results: map[SourceCode:1170: static
1171: int svc_rpcbind_set_version(struct net *net,
1172: const struct svc_program *progp,
1173: u32 version, int family,
1174: unsigned short proto,
1175: unsigned short port)
1176: {
1177: return __svc_register(net, progp->pg_name, progp->pg_prog,
1178: version, family, proto, port);
1179:
1180: }
SourceFile:net/sunrpc/svc.c]
|
| 70/2 |
2026/06/30 00:50 |
llm |
expert |
1m
Model:
Tokens:
input: 63925
output: 36
thoughts: 10
Thoughts: Okay, here's my take on those thoughts, tailored for an expert audience:
**Analyzing the Registration Process**
Right, let's dive straight in. My immediate thought is to check out the `__svc_register` function. It's the lynchpin, isn't it? Everything service-related starts with understanding that registration process. I need to figure out the exact mechanisms here. Where does it reside? Is it in the kernel or perhaps in some lower-level library? What data structures are involved? I need to understand how the services identify and communicate. What kind of hooks or callbacks are established? Any potential race conditions during registration that I need to look out for? Specifically, I'm thinking about the order of registration and how this could relate to dependency injection, and security. What are the permission controls involved with registering services? The more granular understanding I can get, the better.
|
| 71/2 |
2026/06/30 00:51 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/sunrpc/svc.c Name:__svc_register]
Results: map[SourceCode:1140: /*
1141: * Register a kernel RPC service via rpcbind version 4.
1142: *
1143: * Returns zero on success; a negative errno value is returned
1144: * if any error occurs.
1145: */
1146: static int __svc_register(struct net *net, const char *progname,
1147: const u32 program, const u32 version,
1148: const int family,
1149: const unsigned short protocol,
1150: const unsigned short port)
1151: {
1152: int error = -EAFNOSUPPORT;
1153:
1154: switch (family) {
1155: case PF_INET:
1156: error = __svc_rpcb_register4(net, program, version,
1157: protocol, port);
1158: break;
1159: #if IS_ENABLED(CONFIG_IPV6)
1160: case PF_INET6:
1161: error = __svc_rpcb_register6(net, program, version,
1162: protocol, port);
1163: #endif
1164: }
1165:
1166: trace_svc_register(progname, version, family, protocol, port, error);
1167: return error;
1168: }
SourceFile:net/sunrpc/svc.c]
|
| 72/2 |
2026/06/30 00:51 |
llm |
expert |
0m
Model:
Tokens:
input: 64584
output: 40
thoughts: 14
Thoughts: Okay, here's my interpretation of that thought process, assuming I'm deeply familiar with distributed systems and RPC mechanisms:
**Analyzing `__svc_rpcb_register4`**
Alright, let's dive into this. The fact that the thought immediately jumped to `__svc_rpcb_register4` means there's a strong context of RPC and service registration at play here. It's likely I'm debugging something, perhaps troubleshooting a connection issue in an RPC-based distributed application, or maybe I'm reviewing code related to a service discovery process. My expertise means I can quickly infer a lot just from that function name. `__svc` suggests it's likely a system-level or kernel-level function related to the RPC binder service. The `rpcb` part is a dead giveaway - this deals with the RPC binder, which handles service registration and lookup. The `register4` suffix probably refers to a version of the RPC protocol, specifically version 4. Given the prevalence of versioning in distributed systems, the version number is key. I need to be sure I understand the protocol and its implications. Perhaps a client can't find a server, or a server isn't registering properly, and that's why this function is the focus. This function is the pivotal point. Iβll need to understand its behavior, input parameters, what itβs supposed to do, and whether it's executing correctly. I'll need to know if the version is supported, how the call is constructed, and whether it's returning the expected registration status. I'll be looking for potential errors in the process - incorrect program or version numbers, invalid network addresses, authentication issues, or the RPC binder service itself might be having a problem. Time to dig in.
|
| 73/2 |
2026/06/30 00:51 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/sunrpc/svc.c Name:__svc_rpcb_register4]
Results: map[SourceCode:1044: /*
1045: * Register an "inet" protocol family netid with the local
1046: * rpcbind daemon via an rpcbind v4 SET request.
1047: *
1048: * No netconfig infrastructure is available in the kernel, so
1049: * we map IP_ protocol numbers to netids by hand.
1050: *
1051: * Returns zero on success; a negative errno value is returned
1052: * if any error occurs.
1053: */
1054: static int __svc_rpcb_register4(struct net *net, const u32 program,
1055: const u32 version,
1056: const unsigned short protocol,
1057: const unsigned short port)
1058: {
1059: const struct sockaddr_in sin = {
1060: .sin_family = AF_INET,
1061: .sin_addr.s_addr = htonl(INADDR_ANY),
1062: .sin_port = htons(port),
1063: };
1064: const char *netid;
1065: int error;
1066:
1067: switch (protocol) {
1068: case IPPROTO_UDP:
1069: netid = RPCBIND_NETID_UDP;
1070: break;
1071: case IPPROTO_TCP:
1072: netid = RPCBIND_NETID_TCP;
1073: break;
1074: default:
1075: return -ENOPROTOOPT;
1076: }
1077:
1078: error = rpcb_v4_register(net, program, version,
1079: (const struct sockaddr *)&sin, netid);
1080:
1081: /*
1082: * User space didn't support rpcbind v4, so retry this
1083: * registration request with the legacy rpcbind v2 protocol.
1084: */
1085: if (error == -EPROTONOSUPPORT)
1086: error = rpcb_register(net, program, version, protocol, port);
1087:
1088: return error;
1089: }
SourceFile:net/sunrpc/svc.c]
|
| 74/2 |
2026/06/30 00:51 |
llm |
expert |
0m
Model:
Tokens:
input: 65679
output: 39
thoughts: 256
Thoughts: **The Blocking RPC and the Hung Task Mystery**
Okay, so I'm digging into this issue and it's starting to make sense. The `rpcb_v4_register` function, as the name suggests, makes an RPC call. And the problem is that if `rpcbind` isn't running or if it's somehow hung, that RPC call could block. And if it blocks, it blocks the *thread* that's doing the calling.
Now, here's where it gets interesting. I know that `svc_delete_xprt` is called from `svc_clean_up_xprts`, which itself is called from `svc_xprt_destroy_all`. And that `svc_xprt_destroy_all` is called from `nfsd_nl_listener_set_doit`. So, if `rpcb_v4_register` blocks, it effectively blocks `nfsd_nl_listener_set_doit`.
Wait a minute... *that* function, `nfsd_nl_listener_set_doit`, it holds `nfsd_mutex`! So if `rpcb_v4_register` blocks for 143 seconds, that would trigger the hung task timeout, right? And that's exactly what we're seeing!
And further, `nfsd_nl_cache_flush_doit` is *waiting* for `nfsd_mutex`! The pieces are all fitting together. So this potential block in the RPC call completely explains the hung task.
Let's verify this, can `rpcb_v4_register` block indefinitely? I need to check the code to be sure.
|
| 75/2 |
2026/06/30 00:52 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/sunrpc/svc.c Name:rpcb_v4_register]
Results: map[SourceCode: 544: /**
545: * rpcb_v4_register - set or unset a port registration with the local rpcbind
546: * @net: target network namespace
547: * @program: RPC program number of service to (un)register
548: * @version: RPC version number of service to (un)register
549: * @address: address family, IP address, and port to (un)register
550: * @netid: netid of transport protocol to (un)register
551: *
552: * Returns zero if the registration request was dispatched successfully
553: * and the rpcbind daemon returned success. Otherwise, returns an errno
554: * value that reflects the nature of the error (request could not be
555: * dispatched, timed out, or rpcbind returned an error).
556: *
557: * RPC services invoke this function to advertise their contact
558: * information via the system's rpcbind daemon. RPC services
559: * invoke this function once for each [program, version, address,
560: * netid] tuple they wish to advertise.
561: *
562: * Callers may also unregister RPC services that are registered at a
563: * specific address by setting the port number in @address to zero.
564: * They may unregister all registered protocol families at once for
565: * a service by passing a NULL @address argument. If @netid is ""
566: * then all netids for [program, version, address] are unregistered.
567: *
568: * This function uses rpcbind protocol version 4 to contact the
569: * local rpcbind daemon. The local rpcbind daemon must support
570: * version 4 of the rpcbind protocol in order for these functions
571: * to register a service successfully.
572: *
573: * Supported netids include "udp" and "tcp" for UDP and TCP over
574: * IPv4, and "udp6" and "tcp6" for UDP and TCP over IPv6,
575: * respectively.
576: *
577: * The contents of @address determine the address family and the
578: * port to be registered. The usual practice is to pass INADDR_ANY
579: * as the raw address, but specifying a non-zero address is also
580: * supported by this API if the caller wishes to advertise an RPC
581: * service on a specific network interface.
582: *
583: * Note that passing in INADDR_ANY does not create the same service
584: * registration as IN6ADDR_ANY. The former advertises an RPC
585: * service on any IPv4 address, but not on IPv6. The latter
586: * advertises the service on all IPv4 and IPv6 addresses.
587: */
588: int rpcb_v4_register(struct net *net, const u32 program, const u32 version,
589: const struct sockaddr *address, const char *netid)
590: {
591: struct rpcbind_args map = {
592: .r_prog = program,
593: .r_vers = version,
594: .r_netid = netid,
595: .r_owner = RPCB_OWNER_STRING,
596: };
597: struct rpc_message msg = {
598: .rpc_argp = &map,
599: };
600: struct sunrpc_net *sn = net_generic(net, sunrpc_net_id);
601:
602: if (sn->rpcb_local_clnt4 == NULL)
603: return -EPROTONOSUPPORT;
604:
605: if (address == NULL)
606: return rpcb_unregister_all_protofamilies(sn, &msg);
607:
608: trace_rpcb_register(map.r_prog, map.r_vers, map.r_addr, map.r_netid);
609:
610: switch (address->sa_family) {
611: case AF_INET:
612: return rpcb_register_inet4(sn, address, &msg);
613: case AF_INET6:
614: return rpcb_register_inet6(sn, address, &msg);
615: }
616:
617: return -EAFNOSUPPORT;
618: }
SourceFile:net/sunrpc/rpcb_clnt.c]
|
| 76/2 |
2026/06/30 00:52 |
llm |
expert |
0m
Model:
Tokens:
input: 67672
output: 42
thoughts: 128
Thoughts: **Investigating Synchronous RPC Call Behavior**
Okay, so I'm tracing the flow from `rpcb_register_inet4` and it looks like it funnels down through `rpcb_register_call` and then into `rpc_call_sync`. Right, so `rpc_call_sync` is doing a synchronous RPC call, which makes sense. The crucial point here is that if the RPC server, specifically `rpcbind`, isn't responding, we're going to wait. That's fine in principle, but `rpcbind` is local, which raises some flags.
A local daemon not responding usually means it's either crashed, blocked, or in a tight loop. So if `rpcbind` is down, we're likely hitting a timeout, and not just hanging forever. But I need to know *what* timeout we're dealing with. I need to figure out what timeout is set for calls to `rpcbind` in this path. The next step is to examine how `rpcb_local_clnt4` is created. That's where the timeout might be defined. Let's dig into that and see what we can find.
|
| 77/2 |
2026/06/30 00:52 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/sunrpc/rpcb_clnt.c Name:rpcb_create_local]
Results: map[SourceCode: 341: /*
342: * Returns zero on success, otherwise a negative errno value
343: * is returned.
344: */
345: int rpcb_create_local(struct net *net)
346: {
347: static DEFINE_MUTEX(rpcb_create_local_mutex);
348: int result = 0;
349:
350: if (rpcb_get_local(net))
351: return result;
352:
353: mutex_lock(&rpcb_create_local_mutex);
354: if (rpcb_get_local(net))
355: goto out;
356:
357: if (rpcb_create_local_abstract(net) != 0 &&
358: rpcb_create_local_unix(net) != 0)
359: result = rpcb_create_local_net(net);
360:
361: out:
362: mutex_unlock(&rpcb_create_local_mutex);
363: return result;
364: }
SourceFile:net/sunrpc/rpcb_clnt.c]
|
| 78/2 |
2026/06/30 00:52 |
llm |
expert |
0m
Model:
Tokens:
input: 68455
output: 44
thoughts: 596
Thoughts: **Analyzing a Potential Hung Task Timeout in RPC Transport Destruction**
Okay, so I'm looking at this code and trying to understand a possible performance issue during the teardown of RPC transports. My initial thought is that we're creating a local RPC client, probably for some kind of deregistration with rpcbind. The typical timeout for these local clients is usually on the order of 60 seconds. That's fine in isolation, but... hang on. I see `svc_delete_xprt` being called in a loop, and inside that, it's calling `svc_register`. And the purpose of `svc_register` in *this* context is to *unregister* the service! But it might be the reason for the 60 second delay!
Specifically, this snippet is concerning:
```c
if (test_bit(XPT_RPCB_UNREG, &xprt->xpt_flags)) {
struct svc_sock *svsk = container_of(xprt, struct svc_sock,
sk_xprt);
struct socket *sock = svsk->sk_sock;
if (svc_register(serv, xprt->xpt_net, sock->sk->sk_family,
sock->sk->sk_protocol, 0) < 0)
pr_warn("failed to unregister %s with rpcbind\n",
xprt->xpt_class->xcl_name);
}
```
If that `svc_register` call blocks for 60 seconds *per* transport, and we have multiple transports, this becomes a major problem. `svc_xprt_destroy_all` is the culprit. If there are, say, three transports, and each unregister call takes 60 seconds, we are looking at 180 seconds to fully shut down. That's *well* above the usual hung task timeout.
The big question is: Why would `svc_register` block for so long? The answer: `rpcbind` is either unavailable, or, more concerning, dropping packets. It could be that `rpcbind` is not running at all, or perhaps the packet losses are caused by network congestion. However, because we are talking about a local RPC client, it *could* be using a UNIX socket (`rpcb_create_local_unix`) or a loopback connection (`rpcb_create_local_net`). A UNIX socket *shouldn't* drop packets, but...
Here's the kicker: Syzkaller! If syzkaller is fuzzing and has created a *fake* `rpcbind` that just sleeps and doesn't respond, we are *screwed*. Syzkaller can easily bind to the rpcbind port or the UNIX socket, effectively holding the connection open without replying. Then `rpc_call_sync` will timeout. This 60 second timeout could occur because the rpcb client will try to connect, and then fail after a certain period of time. Then this is done for *each* transport sequentially.
I need to confirm the exact timeout value for `rpcb_local_clnt4` to get a handle on this.
|
| 79/2 |
2026/06/30 00:52 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/sunrpc/rpcb_clnt.c Name:rpcb_create_local_unix]
Results: map[SourceCode: 284: static int rpcb_create_local_unix(struct net *net)
285: {
286: static const struct sockaddr_un rpcb_localaddr_unix = {
287: .sun_family = AF_LOCAL,
288: .sun_path = RPCBIND_SOCK_PATHNAME,
289: };
290:
291: return rpcb_create_af_local(net, &rpcb_localaddr_unix);
292: }
SourceFile:net/sunrpc/rpcb_clnt.c]
|
| 80/2 |
2026/06/30 00:52 |
llm |
expert |
1m
Model:
Tokens:
input: 69970
output: 44
thoughts: 14
Thoughts: Okay, let's dive into this. Here's my take on those thoughts, as if they're mine:
**Checking `rpcb_create_af_local`**
Alright, time to focus. I'm thinking, "Let's check `rpcb_create_af_local`." This isn't just a casual glance; I need to really dig into this function. I'm already formulating a mental checklist β what are the key aspects? I'm anticipating questions I'll need to answer about its implementation, any potential gotchas, and any recent modifications that might be relevant. My expertise allows me to quickly prioritize the important aspects. I need to understand its behavior thoroughly, especially concerning any interactions with the underlying OS or hardware. This check is crucial for the task at hand, likely related to networking or inter-process communication, given the function's name. Let's get to work.
|
| 81/2 |
2026/06/30 00:53 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/sunrpc/rpcb_clnt.c Name:rpcb_create_af_local]
Results: map[SourceCode: 224: /*
225: * Returns zero on success, otherwise a negative errno value
226: * is returned.
227: */
228: static int rpcb_create_af_local(struct net *net,
229: const struct sockaddr_un *addr)
230: {
231: struct rpc_create_args args = {
232: .net = net,
233: .protocol = XPRT_TRANSPORT_LOCAL,
234: .address = (struct sockaddr *)addr,
235: .addrsize = SUN_LEN(addr),
236: .servername = "localhost",
237: .program = &rpcb_program,
238: .version = RPCBVERS_2,
239: .authflavor = RPC_AUTH_NULL,
240: .cred = current_cred(),
241: /*
242: * We turn off the idle timeout to prevent the kernel
243: * from automatically disconnecting the socket.
244: * Otherwise, we'd have to cache the mount namespace
245: * of the caller and somehow pass that to the socket
246: * reconnect code.
247: */
248: .flags = RPC_CLNT_CREATE_NO_IDLE_TIMEOUT,
249: };
250: struct rpc_clnt *clnt, *clnt4;
251: int result = 0;
252:
253: /*
254: * Because we requested an RPC PING at transport creation time,
255: * this works only if the user space portmapper is rpcbind, and
256: * it's listening on AF_LOCAL on the named socket.
257: */
258: clnt = rpc_create(&args);
259: if (IS_ERR(clnt)) {
260: result = PTR_ERR(clnt);
261: goto out;
262: }
263:
264: clnt4 = rpc_bind_new_program(clnt, &rpcb_program, RPCBVERS_4);
265: if (IS_ERR(clnt4))
266: clnt4 = NULL;
267:
268: rpcb_set_local(net, clnt, clnt4, true);
269:
270: out:
271: return result;
272: }
SourceFile:net/sunrpc/rpcb_clnt.c]
|
| 82/2 |
2026/06/30 00:53 |
llm |
expert |
0m
Model:
Tokens:
input: 70971
output: 40
thoughts: 127
Thoughts: **Analyzing Potential `rpcbind` Vulnerability**
Okay, so if this `rpc_create` call is successful, that tells me the socket is up and someone's actually listening, right? Now, if Syzkaller's playing a trick and created a fake `rpcbind` on `/var/run/rpcbind.sock` β a "dummy" server, if you will β it could accept the connection without actually doing anything useful.
Then, when `svc_register` kicks off and calls `rpcb_v4_register`, it shoots out an RPC request and just sits there waiting for a response. Since our fake `rpcbind` is configured to just sit on its hands, the whole thing would eventually time out. So, the key question now becomes, what's the timeout value for `XPRT_TRANSPORT_LOCAL`? I need to get that value. Let's dig into `xs_local_setup` and see what it reveals.
|
| 83/2 |
2026/06/30 00:53 |
tool |
codesearch-definition-source |
0m
Error:
Args: map[ContextFile:net/sunrpc/xprtsock.c Name:xs_local_setup]
Results: map[SourceCode: SourceFile:]
|
| 84/2 |
2026/06/30 00:53 |
llm |
expert |
0m
Model:
Tokens:
input: 71364
output: 38
thoughts: 28
Thoughts: Okay, here's my take on those thoughts, framed as an expert's internal monologue:
**Investigating `XPRT_TRANSPORT_LOCAL` in `xprtsock.c`**
Alright, let's dive into this. The immediate goal is to understand what's going on with `XPRT_TRANSPORT_LOCAL`. Given the context of `net/sunrpc/xprtsock.c`, I'm assuming we're dealing with the socket transport implementation within the SunRPC framework, likely focusing on interactions with the network and its underlying transport mechanisms. I need to figure out what functionality or aspects of the `XPRT` (transport) layer utilize the `_LOCAL` designation. Is it related to loopback, inter-process communication within the same host, or something else entirely? A quick search for that specific identifier within the code will hopefully illuminate its purpose and how it's handled. I'm expecting this will define how the RPC framework handles local socket-based communication, which, if I recall correctly, is essential for efficiency gains when the client and server reside on the same machine. Iβll be looking for references to this flag in function calls, conditional branches, or data structures. The file likely contains details on how the network sockets are set up, how data is marshaled, and the process of client-server interaction on a single host. I'm curious if this has any implications for security or performance considerations, particularly around inter-process communication versus network sockets. So, let's get the search going and see what we find.
|
| 85/2 |
2026/06/30 00:53 |
tool |
grepper |
0m
Args: map[Expression:XPRT_TRANSPORT_LOCAL PathPrefix:net/sunrpc/xprtsock.c]
Results: map[Output:net/sunrpc/xprtsock.c=3625=static struct xprt_class xs_local_transport = {
--
net/sunrpc/xprtsock.c-3628- .owner = THIS_MODULE,
net/sunrpc/xprtsock.c:3629: .ident = XPRT_TRANSPORT_LOCAL,
net/sunrpc/xprtsock.c-3630- .setup = xs_setup_local,
]
|
| 86/2 |
2026/06/30 00:53 |
llm |
expert |
0m
Model:
Tokens:
input: 71894
output: 40
thoughts: 11
Thoughts: Okay, let's dive into this. Here's how I'd approach summarizing the prompt, given my expertise:
**Checking `xs_setup_local`**
Alright, the instruction is to essentially "think aloud" about the implied task of checking `xs_setup_local`. It's a pretty open-ended directive, and that's good. In my line of work, that means I'll need to start by understanding what's *implied*. `xs_setup_local`... that suggests it's likely a configuration or initialization script, probably related to a local environment. It's probably part of some larger system, likely a build or deployment process, maybe for testing or development. I should start by looking for context cues. What system is this script a part of? I'll probably need to know the relevant technologies and their integrations. The wording suggests *local*, so I'd infer this isn't a production setup. I'll need to use that context to figure out what kind of system will use it and how that might affect how it's written and what's important. This means I will begin by thinking about the relevant assumptions and considerations. From there, I'll need to figure out what's important to look for and where I'd start.
|
| 87/2 |
2026/06/30 00:53 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/sunrpc/xprtsock.c Name:xs_setup_local]
Results: map[SourceCode:3228: /**
3229: * xs_setup_local - Set up transport to use an AF_LOCAL socket
3230: * @args: rpc transport creation arguments
3231: *
3232: * AF_LOCAL is a "tpi_cots_ord" transport, just like TCP
3233: */
3234: static struct rpc_xprt *xs_setup_local(struct xprt_create *args)
3235: {
3236: struct sockaddr_un *sun = (struct sockaddr_un *)args->dstaddr;
3237: struct sock_xprt *transport;
3238: struct rpc_xprt *xprt;
3239: struct rpc_xprt *ret;
3240:
3241: xprt = xs_setup_xprt(args, xprt_tcp_slot_table_entries,
3242: xprt_max_tcp_slot_table_entries);
3243: if (IS_ERR(xprt))
3244: return xprt;
3245: transport = container_of(xprt, struct sock_xprt, xprt);
3246:
3247: xprt->prot = 0;
3248: xprt->xprt_class = &xs_local_transport;
3249: xprt->max_payload = RPC_MAX_FRAGMENT_SIZE;
3250:
3251: xprt->bind_timeout = XS_BIND_TO;
3252: xprt->reestablish_timeout = XS_TCP_INIT_REEST_TO;
3253: xprt->idle_timeout = XS_IDLE_DISC_TO;
3254:
3255: xprt->ops = &xs_local_ops;
3256: xprt->timeout = &xs_local_default_timeout;
3257:
3258: INIT_WORK(&transport->recv_worker, xs_stream_data_receive_workfn);
3259: INIT_WORK(&transport->error_worker, xs_error_handle);
3260: INIT_DELAYED_WORK(&transport->connect_worker, xs_dummy_setup_socket);
3261:
3262: switch (sun->sun_family) {
3263: case AF_LOCAL:
3264: if (sun->sun_path[0] != '/' && sun->sun_path[0] != '\0') {
3265: dprintk("RPC: bad AF_LOCAL address: %s\n",
3266: sun->sun_path);
3267: ret = ERR_PTR(-EINVAL);
3268: goto out_err;
3269: }
3270: xprt_set_bound(xprt);
3271: xs_format_peer_addresses(xprt, "local", RPCBIND_NETID_LOCAL);
3272: break;
3273: default:
3274: ret = ERR_PTR(-EAFNOSUPPORT);
3275: goto out_err;
3276: }
3277:
3278: dprintk("RPC: set up xprt to %s via AF_LOCAL\n",
3279: xprt->address_strings[RPC_DISPLAY_ADDR]);
3280:
3281: if (try_module_get(THIS_MODULE))
3282: return xprt;
3283: ret = ERR_PTR(-EINVAL);
3284: out_err:
3285: xs_xprt_free(xprt);
3286: return ret;
3287: }
SourceFile:net/sunrpc/xprtsock.c]
|
| 88/2 |
2026/06/30 00:53 |
llm |
expert |
0m
Model:
Tokens:
input: 73269
output: 42
thoughts: 13
Thoughts: Here's my take on those thoughts:
**Checking a Key Configuration Setting**
Okay, let's zero in on this `xs_local_default_timeout` setting. I need to quickly refresh my memory on what this controls and its implications. I know its important, but I need to make sure I understand the scope of its control and what it impacts. I wonder if any recent changes have been made. My gut tells me this will be an important setting to keep a close eye on.
|
| 89/2 |
2026/06/30 00:53 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:net/sunrpc/xprtsock.c Name:xs_local_default_timeout]
Results: map[SourceCode:3222: static const struct rpc_timeout xs_local_default_timeout = {
3223: .to_initval = 10 * HZ,
3224: .to_maxval = 10 * HZ,
3225: .to_retries = 2,
3226: };
SourceFile:net/sunrpc/xprtsock.c]
|
| 90/2 |
2026/06/30 00:53 |
llm |
expert |
1m
Model:
Tokens:
input: 73549
output: 65
thoughts: 729
Thoughts: **The Hung Task Mystery Solved**
Okay, let's break this down. The problem seems to be a classic race condition causing a hung task, and I think I've figured out why. The timeout for an RPC call is 10 seconds, with two retries. Thatβs a total of 30 seconds per call. If we're talking about unregistering 5 transports, that's a total of 150 seconds. That's longer than the hung task timeout (143 seconds). Bingo.
The key seems to be a crafty exploit using a fake `rpcbind`. If `syzkaller` creates a dummy `rpcbind` on `/var/run/rpcbind.sock`, and then makes 5 NFS listeners, and then deletes them, it *should* block for 150 seconds, while holding the `nfsd_mutex` lock. That duration would be what caused the hung task error.
Now, can we actually create a fake `rpcbind`? Yes, any process with appropriate permissions can bind to a UNIX socket. The problem is `/var/run/rpcbind.sock` is normally in `/var/run`, which is root-owned. But wait, `syzkaller` runs in a user namespace, where it can mount a tmpfs on `/var/run`! That's the loophole.
I need to confirm if `rpcb_create_local_unix` uses the network namespace's `/var/run` or the host's. It's hardcoded to `/var/run/rpcbind.sock`. So, if syzkaller mounts a tmpfs on `/var/run` inside its mount namespace, it can create the socket, and then `rpcb_create_local_unix` will connect to it. `syzkaller` then just accepts the connection and sleeps.
Now, call `nfsd_nl_listener_set_doit` to create 5 listeners. Then again, delete them. This calls `svc_xprt_destroy_all` that then calls `svc_delete_xprt`. Each `svc_delete_xprt` then calls `svc_register` to unregister. This leads to `rpcb_v4_register`, which triggers an RPC call, and that's the slow, blocking part. That RPC call timeouts after 30 seconds.
Five listeners * 30 seconds = 150 seconds of holding `nfsd_mutex`. In the meantime, another thread calls `nfsd_nl_cache_flush_doit` which tries to acquire the same `nfsd_mutex`. This second thread will block, because of the 150 second lock, and triggers the hung task.
So, this is a clear denial-of-service vulnerability using a fake rpcbind and lengthy timeouts. Fortunately, it's just a timeout, not a more dangerous exploit. It's accessible from unprivileged processes because `syzkaller` runs as a non-privileged user in a user namespace. The exploit needs `CAP_SYS_ADMIN` in the user namespace to mount a tmpfs on `/var/run` and create the socket. It also requires `CAP_NET_ADMIN` to configure netlink, since `nfsd_nl_listener_set_doit` is a genetlink command. Let's make sure that `nfsd_nl_listener_set_doit` truly requires `CAP_NET_ADMIN` by checking the policy.
|
| 91/2 |
2026/06/30 00:54 |
tool |
codesearch-find-references |
0m
Args: map[ContextFile:fs/nfsd/nfsctl.c IncludeSnippetLines:2 Name:nfsd_nl_listener_set_doit SourceTreePrefix:fs/nfsd]
Results: map[References:[map[ReferenceKind:takes-address-of ReferencingEntityKind:global_variable ReferencingEntityName:nfsd_nl_ops SourceFile:fs/nfsd/netlink.c SourceLine:154 SourceSnippet: 152: {
153: .cmd = NFSD_CMD_LISTENER_SET,
154: .doit = nfsd_nl_listener_set_doit,
155: .policy = nfsd_listener_set_nl_policy,
156: .maxattr = NFSD_A_SERVER_SOCK_ADDR,
]] TruncatedOutput:false]
|
| 92/2 |
2026/06/30 00:54 |
llm |
expert |
0m
Model:
Tokens:
input: 75284
output: 41
thoughts: 26
Thoughts: Okay, let's dive into this. Here's my thought process on what I'm about to do, from my perspective as an expert in the field:
**Investigating `nfsd_nl_ops`**
Right, so I'm thinking I need to understand something related to NFS and netlink. The place to start, given my experience, is almost certainly `fs/nfsd/netlink.c`. I expect to find some of the core netlink operations pertaining to the NFS daemon there. Specifically, I need to understand how the netlink interfaces are set up. Iβm thinking there will be a structure defining the netlink operations; most likely named `nfsd_nl_ops`, that manages all of the interactions. I'm going to carefully read this section and get a full understanding of what's going on.
|
| 93/2 |
2026/06/30 00:54 |
tool |
codesearch-definition-source |
0m
Args: map[ContextFile:fs/nfsd/netlink.c Name:nfsd_nl_ops]
Results: map[SourceCode: 121: /* Ops table for nfsd */
122: static const struct genl_split_ops nfsd_nl_ops[] = {
123: {
124: .cmd = NFSD_CMD_RPC_STATUS_GET,
125: .dumpit = nfsd_nl_rpc_status_get_dumpit,
126: .flags = GENL_CMD_CAP_DUMP,
127: },
128: {
129: .cmd = NFSD_CMD_THREADS_SET,
130: .doit = nfsd_nl_threads_set_doit,
131: .policy = nfsd_threads_set_nl_policy,
132: .maxattr = NFSD_A_SERVER_FH_KEY,
133: .flags = GENL_ADMIN_PERM | GENL_CMD_CAP_DO,
134: },
135: {
136: .cmd = NFSD_CMD_THREADS_GET,
137: .doit = nfsd_nl_threads_get_doit,
138: .flags = GENL_CMD_CAP_DO,
139: },
140: {
141: .cmd = NFSD_CMD_VERSION_SET,
142: .doit = nfsd_nl_version_set_doit,
143: .policy = nfsd_version_set_nl_policy,
144: .maxattr = NFSD_A_SERVER_PROTO_VERSION,
145: .flags = GENL_ADMIN_PERM | GENL_CMD_CAP_DO,
146: },
147: {
148: .cmd = NFSD_CMD_VERSION_GET,
149: .doit = nfsd_nl_version_get_doit,
150: .flags = GENL_CMD_CAP_DO,
151: },
152: {
153: .cmd = NFSD_CMD_LISTENER_SET,
154: .doit = nfsd_nl_listener_set_doit,
155: .policy = nfsd_listener_set_nl_policy,
156: .maxattr = NFSD_A_SERVER_SOCK_ADDR,
157: .flags = GENL_ADMIN_PERM | GENL_CMD_CAP_DO,
158: },
159: {
160: .cmd = NFSD_CMD_LISTENER_GET,
161: .doit = nfsd_nl_listener_get_doit,
162: .flags = GENL_CMD_CAP_DO,
163: },
164: {
165: .cmd = NFSD_CMD_POOL_MODE_SET,
166: .doit = nfsd_nl_pool_mode_set_doit,
167: .policy = nfsd_pool_mode_set_nl_policy,
168: .maxattr = NFSD_A_POOL_MODE_MODE,
169: .flags = GENL_ADMIN_PERM | GENL_CMD_CAP_DO,
170: },
171: {
172: .cmd = NFSD_CMD_POOL_MODE_GET,
173: .doit = nfsd_nl_pool_mode_get_doit,
174: .flags = GENL_CMD_CAP_DO,
175: },
176: {
177: .cmd = NFSD_CMD_SVC_EXPORT_GET_REQS,
178: .dumpit = nfsd_nl_svc_export_get_reqs_dumpit,
179: .flags = GENL_ADMIN_PERM | GENL_CMD_CAP_DUMP,
180: },
181: {
182: .cmd = NFSD_CMD_SVC_EXPORT_SET_REQS,
183: .doit = nfsd_nl_svc_export_set_reqs_doit,
184: .policy = nfsd_svc_export_set_reqs_nl_policy,
185: .maxattr = NFSD_A_SVC_EXPORT_REQS_REQUESTS,
186: .flags = GENL_ADMIN_PERM | GENL_CMD_CAP_DO,
187: },
188: {
189: .cmd = NFSD_CMD_EXPKEY_GET_REQS,
190: .dumpit = nfsd_nl_expkey_get_reqs_dumpit,
191: .flags = GENL_ADMIN_PERM | GENL_CMD_CAP_DUMP,
192: },
193: {
194: .cmd = NFSD_CMD_EXPKEY_SET_REQS,
195: .doit = nfsd_nl_expkey_set_reqs_doit,
196: .policy = nfsd_expkey_set_reqs_nl_policy,
197: .maxattr = NFSD_A_EXPKEY_REQS_REQUESTS,
198: .flags = GENL_ADMIN_PERM | GENL_CMD_CAP_DO,
199: },
200: {
201: .cmd = NFSD_CMD_CACHE_FLUSH,
202: .doit = nfsd_nl_cache_flush_doit,
203: .policy = nfsd_cache_flush_nl_policy,
204: .maxattr = NFSD_A_CACHE_FLUSH_MASK,
205: .flags = GENL_ADMIN_PERM | GENL_CMD_CAP_DO,
206: },
207: {
208: .cmd = NFSD_CMD_UNLOCK_IP,
209: .doit = nfsd_nl_unlock_ip_doit,
210: .policy = nfsd_unlock_ip_nl_policy,
211: .maxattr = NFSD_A_UNLOCK_IP_ADDRESS,
212: .flags = GENL_ADMIN_PERM | GENL_CMD_CAP_DO,
213: },
214: {
215: .cmd = NFSD_CMD_UNLOCK_FILESYSTEM,
216: .doit = nfsd_nl_unlock_filesystem_doit,
217: .policy = nfsd_unlock_filesystem_nl_policy,
218: .maxattr = NFSD_A_UNLOCK_FILESYSTEM_PATH,
219: .flags = GENL_ADMIN_PERM | GENL_CMD_CAP_DO,
220: },
221: {
222: .cmd = NFSD_CMD_UNLOCK_EXPORT,
223: .doit = nfsd_nl_unlock_export_doit,
224: .policy = nfsd_unlock_export_nl_policy,
225: .maxattr = NFSD_A_UNLOCK_EXPORT_PATH,
226: .flags = GENL_ADMIN_PERM | GENL_CMD_CAP_DO,
227: },
228: };
SourceFile:fs/nfsd/netlink.c]
|
| 94/2 |
2026/06/30 00:54 |
llm |
expert |
0m
Model:
Tokens:
input: 77624
output: 66
thoughts: 1948
Thoughts: **Analysis of the NFSD_CMD_LISTENER_SET Vulnerability**
Okay, let's break this down. `NFSD_CMD_LISTENER_SET` has permissions that include `GENL_ADMIN_PERM`, meaning it requires `CAP_NET_ADMIN`. Since syzkaller can run in a user namespace, and has `CAP_NET_ADMIN` in that namespace, this vulnerability *is* accessible from user namespaces.
Initially, I suspected this was a Denial of Service (DoS) due to a hung task timeout, potentially caused by the `nfsd_mutex` being held for an extended period, blocking NFS operations. The concern, as with any hung task, is that it can affect the local nfsd instance and in the worst-case, trigger a system panic if the hung task timeout is configured that way. The immediate impact is a DoS.
My initial thought was to rule out any memory corruption, but it became clear that the issue wasn't related to memory. It seemed to involve a long loop or sleep while holding a mutex, but I needed to understand the mechanics further.
Initially, I considered an infinite loop if `svc_xprt_destroy_all` looped forever because `svc_close_list` kept returning > 0. I traced this flow. It starts with the transport being busy. `XPT_BUSY` means `svc_xprt_enqueue` returns immediately. Then, `svc_clean_up_xprts` doesn't find it. But, then `svc_close_list` *does* find it, sets `XPT_CLOSE`, calls `svc_xprt_enqueue` (which returns immediately) and `svc_close_list` returns 1. After that `svc_xprt_destroy_all` calls `svc_clean_up_xprts` (which does nothing), and `msleep(delay++)` which loops again.
I was getting closer, but I needed to understand why the loop continued. I realised that this looked like an infinite loop because `XPT_BUSY` was *never* cleared! And why? Because there were NO active threads (`sv_nrthreads == 0`) and the transport wasn't in `pool->sp_xprts`. I was expecting the transport to be enqueued from `svc_xprt_enqueue` (setting `XPT_BUSY` and enqueuing) but then `svc_clean_up_xprts` dequeued it, but didn't delete it. I checked the code. `svc_clean_up_xprts` deletes a transport if `xprt->xpt_net != net`.
The `nfsd_nl_listener_set_doit` code only puts transports that have `xprt->xpt_net == net` in `sv_permsocks`, but, wait, there's a problem:
```c
/* Put back any matching sockets */
list_for_each_entry_safe(xprt, tmp, &permsocks, xpt_list) {
/* This shouldn't be possible */
if (WARN_ON_ONCE(xprt->xpt_net != net)) {
list_move(&xprt->xpt_list, &serv->sv_permsocks);
continue;
}
```
If `xprt->xpt_net != net`, the transport gets moved back to `sv_permsocks`!
Now `svc_xprt_destroy_all(serv, net, false)` is called, and `svc_close_list` iterates over `sv_permsocks`. I found that if `xprt->xpt_net != net`, `svc_close_list` just ignores it.
Then I had to consider the scenario where `svc_delete_xprt` is called, but returns early because `XPT_DEAD` is already set. If `XPT_DEAD` is set, `svc_delete_xprt` *has already* been called and the transport was removed from `sv_permsocks`. But there was one important corner case: what if `svc_delete_xprt` blocks in `svc_register`?
If it blocked, it would mean `XPT_DEAD` would *not yet* be set and the transport would still be in `sv_permsocks`! Crucially, `svc_register` is called *before* `test_and_set_bit(XPT_DEAD)`! This means the transport can remain in `sv_permsocks` until the call completes. `svc_delete_xprt` is called from `svc_clean
|
| 95/2 |
2026/06/30 00:55 |
tool |
set-results |
0m
Args: map[DenialOfService:true Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:false UserNamespace:true VMGuestTrigger:false VMHostTrigger:false]
Results: map[DenialOfService:true Exploitable:false FilesystemTrigger:false NetworkTrigger:false PeripheralTrigger:false RemoteTrigger:false Unprivileged:false UserNamespace:true VMGuestTrigger:false VMHostTrigger:false]
|
| 96/2 |
2026/06/30 00:55 |
llm |
expert |
0m
Model:
Tokens:
input: 80727
output: 576
thoughts: 419
Thoughts: **Final Thoughts on the DoS Bug**
Okay, the analysis is complete, and it's time to craft the final response. My findings are definitive: we're looking at a Denial of Service vulnerability, and the root cause is a lengthy timeout issue. It all boils down to a prolonged wait within `rpcb_v4_register` while the critical `nfsd_mutex` is held.
Here's the breakdown: When we're removing listeners using `nfsd_nl_listener_set_doit`, it calls `svc_xprt_destroy_all`. This, in turn, iterates through each listener, triggering `svc_delete_xprt` for each. Now, here's where the problem arises: `svc_delete_xprt` attempts to unregister the service with `rpcbind`, and that involves a chain of calls: `svc_register` -> `__svc_register` -> `__svc_rpcb_register4` -> `rpcb_v4_register`.
The exploit is relatively straightforward. A malicious user can craft a fake `rpcbind` server. We can imagine them mounting a `tmpfs` over `/var/run` and then binding a UNIX socket to `/var/run/rpcbind.sock`. Now they can accept connections and just sit on them. They can choose to just ignore all the requests. The RPC client is stuck waiting for a response that will never arrive. On local transports, this timeout is a hefty 30 seconds.
The situation becomes critical when multiple listeners are being removed simultaneously. Those timeouts stack up, so 5 listeners result in 150 seconds of waiting. This exceeds the hung task timeout of 143 seconds. Because `nfsd_nl_listener_set_doit` is stubbornly holding that `nfsd_mutex` lock, any other task wanting that lock, say `nfsd_nl_cache_flush_doit`, will block indefinitely. This blockage will, of course, lead to a hung task panic.
The worrying aspect is that this is exploitable from a user namespace. The `nfsd_nl_listener_set_doit` function is triggered by a netlink command. Critically, to use this command you need the `CAP_NET_ADMIN` capability. But, a user/network namespace can provide this to a user, which means they can run this code in their own isolated environment and trigger the DoS.
Thankfully, this isn't a memory corruption issue or privilege escalation β it's just a reliable Denial of Service.
|
| 97/1 |
2026/06/30 00:55 |
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:
**Bug Mechanism:**
The bug is a Denial of Service (DoS) caused by a long timeout while holding a
global mutex (`nfsd_mutex`).
When a user sends a netlink message to configure NFSD listeners via
`nfsd_nl_listener_set_doit`, the kernel may need to delete existing listeners.
This is done by calling `svc_xprt_destroy_all()`, which iterates over the
transports and calls `svc_delete_xprt()` for each one.
Before fully destroying the transport, `svc_delete_xprt()` attempts to
unregister the service from the local `rpcbind` daemon by calling
`svc_register()` -> `rpcb_v4_register()`. This function performs a synchronous
RPC call to the local `rpcbind` UNIX socket (`/var/run/rpcbind.sock`).
If a malicious user sets up a fake, unresponsive `rpcbind` server (e.g., by
mounting a tmpfs over `/var/run` and binding a UNIX socket to that path), the
RPC call will block until it times out. The default timeout for local RPC
transports is 30 seconds (10 seconds base timeout with 2 retries). If multiple
listeners are being deleted simultaneously, these timeouts accumulate
sequentially (e.g., 5 listeners * 30 seconds = 150 seconds).
Because `nfsd_nl_listener_set_doit()` holds `nfsd_mutex` during this entire
process, any other task attempting to acquire `nfsd_mutex` (such as
`nfsd_nl_cache_flush_doit` seen in the crash trace) will be blocked for an
extended period, eventually triggering the kernel's hung task panic (which
defaults to 143 seconds in syzkaller).
**Exploitability:**
This is a pure Denial of Service (DoS) vulnerability. There is no memory
corruption, out-of-bounds access, or use-after-free involved. It cannot be used
for privilege escalation or information leaks.
**Accessibility:**
The bug can be triggered from an unprivileged process, provided it can create a
new user and network namespace. The `nfsd_nl_listener_set_doit` netlink command
requires `CAP_NET_ADMIN`, which a user can acquire within a new user/network
namespace. Furthermore, creating the fake `rpcbind` socket requires
`CAP_SYS_ADMIN` in the user namespace to mount a tmpfs over `/var/run`. Both of
these are standard capabilities available to unprivileged users utilizing user
namespaces.]
|