KASAN: slab-use-after-free Read in check_tty_count

Status: premoderation: reported syz repro on 2026/08/11 15:00
Bug presence: origin:upstream
[Documentation on labels]
Reported-by: syzbot+717091956325d5178e56@syzkaller.appspotmail.com
First crash: 7d00h, last: 6d23h
▶ ▼ Bug presence (2)
Date Name Commit Repro Result
2026/08/17 lts (merge base) 8c9d5557c8e6 syz [report] KASAN: slab-use-after-free Read in check_tty_count
2026/08/17 upstream (ToT) 8d3ae59288f1 syz [report] KASAN: slab-use-after-free Read in check_tty_count
▶ ▼ Similar bugs (4)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KASAN: slab-use-after-free Read in check_tty_count serial prio:normal 19 syz, C error 2 4d10h 1d02h 0/29 upstream: reported C repro on 2026/08/17 13:05
android-5-15 KASAN: use-after-free Read in check_tty_count 19 syz, C 1 5d11h 5d11h 0/2 upstream: reported C repro on 2026/08/13 03:54
android-6-1 KASAN: use-after-free Read in check_tty_count 19 syz, C 3 8d03h 8d04h 0/2 upstream: reported C repro on 2026/08/10 10:56
android-5-10 KASAN: use-after-free Read in check_tty_count 19 syz, C 2 8d12h 8d12h 0/2 upstream: reported C repro on 2026/08/10 02:57

Sample crash report:
==================================================================
BUG: KASAN: slab-use-after-free in instrument_atomic_read include/linux/instrumented.h:68 [inline]
BUG: KASAN: slab-use-after-free in _test_bit include/asm-generic/bitops/instrumented-non-atomic.h:141 [inline]
BUG: KASAN: slab-use-after-free in tty_port_kopened include/linux/tty_port.h:229 [inline]
BUG: KASAN: slab-use-after-free in check_tty_count+0x1a5/0x330 drivers/tty/tty_io.c:288
Read of size 8 at addr ffff888104b58100 by task syz.4.17/408

CPU: 0 UID: 0 PID: 408 Comm: syz.4.17 Not tainted syzkaller #0 55bf8b22bdada172f4c106b01602b1dfb2209583
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 <TASK>
 __dump_stack+0x21/0x30 lib/dump_stack.c:94
 dump_stack_lvl+0x140/0x1c0 lib/dump_stack.c:120
 print_address_description+0x71/0x210 mm/kasan/report.c:377
 print_report+0x4a/0x70 mm/kasan/report.c:481
 kasan_report+0x162/0x1a0 mm/kasan/report.c:594
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x25a/0x2b0 mm/kasan/generic.c:189
 __kasan_check_read+0x15/0x20 mm/kasan/shadow.c:31
 instrument_atomic_read include/linux/instrumented.h:68 [inline]
 _test_bit include/asm-generic/bitops/instrumented-non-atomic.h:141 [inline]
 tty_port_kopened include/linux/tty_port.h:229 [inline]
 check_tty_count+0x1a5/0x330 drivers/tty/tty_io.c:288
 tty_release+0x89/0x11e0 drivers/tty/tty_io.c:1737
 __fput+0x208/0xa30 fs/file_table.c:447
 ____fput+0x20/0x30 fs/file_table.c:475
 task_work_run+0x1e8/0x260 kernel/task_work.c:246
 ptrace_notify+0x25a/0x290 kernel/signal.c:2419
 ptrace_report_syscall include/linux/ptrace.h:415 [inline]
 ptrace_report_syscall_exit include/linux/ptrace.h:477 [inline]
 syscall_exit_work+0x84/0x150 kernel/entry/common.c:173
 syscall_exit_to_user_mode_prepare+0x21/0x40 kernel/entry/common.c:200
 __syscall_exit_to_user_mode_work kernel/entry/common.c:205 [inline]
 syscall_exit_to_user_mode+0x15/0xb0 kernel/entry/common.c:218
 do_syscall_64+0x63/0xf0 arch/x86/entry/common.c:84
 entry_SYSCALL_64_after_hwframe+0x76/0x7e
RIP: 0033:0x7fe8d4b9e0d9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffd499d7d08 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 00007fe8d4e27da0 RCX: 00007fe8d4b9e0d9
RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
RBP: 00007fe8d4e27da0 R08: 00007fe8d4e26038 R09: 0000000000000000
R10: 000000000003fda0 R11: 0000000000000246 R12: 0000000000011987
R13: 00007fe8d4e25fac R14: 00000000000116da R15: 00007ffd499d7e10
 </TASK>

Allocated by task 409:
 kasan_save_stack mm/kasan/common.c:49 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:70
 kasan_save_alloc_info+0x3a/0x50 mm/kasan/generic.c:565
 poison_kmalloc_redzone mm/kasan/common.c:379 [inline]
 __kasan_kmalloc+0x96/0xb0 mm/kasan/common.c:396
 kasan_kmalloc include/linux/kasan.h:261 [inline]
 __kmalloc_cache_noprof+0x23c/0x470 mm/slub.c:4426
 kmalloc_noprof include/linux/slab.h:881 [inline]
 kzalloc_noprof include/linux/slab.h:1017 [inline]
 gs_port_alloc drivers/usb/gadget/function/u_serial.c:1181 [inline]
 gserial_alloc_line_no_console+0x245/0x770 drivers/usb/gadget/function/u_serial.c:1261
 gserial_alloc_line+0x19/0x30 drivers/usb/gadget/function/u_serial.c:1295
 acm_alloc_instance+0xd7/0x1e0 drivers/usb/gadget/function/f_acm.c:891
 try_get_usb_function_instance drivers/usb/gadget/functions.c:28 [inline]
 usb_get_function_instance+0xfa/0x320 drivers/usb/gadget/functions.c:44
 function_make+0x125/0x370 drivers/usb/gadget/configfs.c:631
 configfs_mkdir+0x526/0xb70 fs/configfs/dir.c:1339
 vfs_mkdir+0x591/0x810 fs/namei.c:4265
 do_mkdirat+0x240/0x530 fs/namei.c:4288
 __do_sys_mkdirat fs/namei.c:4303 [inline]
 __se_sys_mkdirat fs/namei.c:4301 [inline]
 __x64_sys_mkdirat+0x8b/0xa0 fs/namei.c:4301
 x64_sys_call+0x2ba8/0x2ee0 arch/x86/include/generated/asm/syscalls_64.h:259
 do_syscall_x64 arch/x86/entry/common.c:47 [inline]
 do_syscall_64+0x57/0xf0 arch/x86/entry/common.c:78
 entry_SYSCALL_64_after_hwframe+0x76/0x7e

Freed by task 409:
 kasan_save_stack mm/kasan/common.c:49 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:70
 kasan_save_free_info+0x44/0x50 mm/kasan/generic.c:579
 poison_slab_object mm/kasan/common.c:249 [inline]
 __kasan_slab_free+0x5f/0x80 mm/kasan/common.c:266
 kasan_slab_free include/linux/kasan.h:234 [inline]
 slab_free_hook mm/slub.c:2445 [inline]
 slab_free mm/slub.c:4714 [inline]
 kfree+0x158/0x440 mm/slub.c:4875
 gserial_free_port+0x244/0x2e0 drivers/usb/gadget/function/u_serial.c:1225
 gserial_free_line+0x9f/0x1b0 drivers/usb/gadget/function/u_serial.c:1242
 acm_free_instance+0x3d/0x60 drivers/usb/gadget/function/f_acm.c:875
 usb_put_function_instance+0x9f/0xc0 drivers/usb/gadget/functions.c:77
 acm_attr_release+0x19/0x30 drivers/usb/gadget/function/f_acm.c:793
 config_item_cleanup fs/configfs/item.c:128 [inline]
 config_item_release fs/configfs/item.c:137 [inline]
 kref_put include/linux/kref.h:65 [inline]
 config_item_put+0x178/0x240 fs/configfs/item.c:149
 configfs_rmdir+0x8e8/0x9b0 fs/configfs/dir.c:1550
 vfs_rmdir+0x3de/0x560 fs/namei.c:4348
 do_rmdir+0x29a/0x590 fs/namei.c:4407
 __do_sys_rmdir fs/namei.c:4426 [inline]
 __se_sys_rmdir fs/namei.c:4424 [inline]
 __x64_sys_rmdir+0x4b/0x60 fs/namei.c:4424
 x64_sys_call+0xaf7/0x2ee0 arch/x86/include/generated/asm/syscalls_64.h:85
 do_syscall_x64 arch/x86/entry/common.c:47 [inline]
 do_syscall_64+0x57/0xf0 arch/x86/entry/common.c:78
 entry_SYSCALL_64_after_hwframe+0x76/0x7e

The buggy address belongs to the object at ffff888104b58000
 which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 256 bytes inside of
 freed 1024-byte region [ffff888104b58000, ffff888104b58400)

The buggy address belongs to the physical page:
page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x104b58
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0x4000000000000040(head|zone=1)
page_type: f5(slab)
raw: 4000000000000040 ffff888100041dc0 ffffea00040ffc00 0000000000000002
raw: 0000000000000000 0000000000100010 00000001f5000000 0000000000000000
head: 4000000000000040 ffff888100041dc0 ffffea00040ffc00 0000000000000002
head: 0000000000000000 0000000000100010 00000001f5000000 0000000000000000
head: 4000000000000003 ffffea000412d601 ffffffffffffffff 0000000000000000
head: 0000000000000008 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0x252800(GFP_NOWAIT|__GFP_NORETRY|__GFP_COMP|__GFP_THISNODE), pid 46, tgid 46 (kworker/u8:2), ts 3402457909, free_ts 0
 set_page_owner include/linux/page_owner.h:35 [inline]
 post_alloc_hook+0x37d/0x3b0 mm/page_alloc.c:1863
 prep_new_page+0x2d/0x180 mm/page_alloc.c:1871
 get_page_from_freelist+0x4aea/0x4ba0 mm/page_alloc.c:3948
 __alloc_pages_noprof+0x35a/0x7e0 mm/page_alloc.c:5315
 alloc_slab_page+0x6b/0x1e0 mm/slub.c:-1
 allocate_slab+0x69/0x430 mm/slub.c:2687
 new_slab mm/slub.c:2741 [inline]
 ___slab_alloc+0x591/0x8c0 mm/slub.c:3934
 __slab_alloc mm/slub.c:4025 [inline]
 __slab_alloc_node mm/slub.c:4078 [inline]
 slab_alloc_node mm/slub.c:4239 [inline]
 __kmalloc_cache_node_noprof+0x2ae/0x430 mm/slub.c:4434
 kmalloc_node_noprof include/linux/slab.h:904 [inline]
 blk_mq_alloc_hctx block/blk-mq.c:4043 [inline]
 blk_mq_alloc_and_init_hctx+0x1b4/0x1060 block/blk-mq.c:4545
 blk_mq_realloc_hw_ctxs+0x19f/0x940 block/blk-mq.c:4578
 blk_mq_init_allocated_queue+0x3e1/0x1700 block/blk-mq.c:4632
 blk_mq_alloc_queue+0x1c7/0x2f0 block/blk-mq.c:4445
 scsi_alloc_sdev+0x75d/0xcc0 drivers/scsi/scsi_scan.c:337
 scsi_probe_and_add_lun+0x1e9/0x3e60 drivers/scsi/scsi_scan.c:1207
 __scsi_scan_target+0x1f1/0xc20 drivers/scsi/scsi_scan.c:1754
 scsi_scan_channel drivers/scsi/scsi_scan.c:1842 [inline]
 scsi_scan_host_selected+0x352/0x610 drivers/scsi/scsi_scan.c:1871
page_owner free stack trace missing

Memory state around the buggy address:
 ffff888104b58000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888104b58080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888104b58100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff888104b58180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888104b58200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
------------[ cut here ]------------
WARNING: CPU: 0 PID: 408 at drivers/usb/gadget/function/u_serial.c:691 gs_close+0x181/0x9c0 drivers/usb/gadget/function/u_serial.c:691
Modules linked in:
CPU: 0 UID: 0 PID: 408 Comm: syz.4.17 Tainted: G    B              syzkaller #0 55bf8b22bdada172f4c106b01602b1dfb2209583
Tainted: [B]=BAD_PAGE
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:gs_close+0x181/0x9c0 drivers/usb/gadget/function/u_serial.c:691
Code: 62 cc fd 41 ff cc 42 0f b6 04 2b 84 c0 0f 85 da 06 00 00 48 8b 44 24 20 44 89 20 48 8b 5c 24 38 e9 d1 02 00 00 e8 7f 62 cc fd <0f> 0b 48 8b 5c 24 38 e9 c0 02 00 00 e8 6e 62 cc fd 49 8d bf 78 02
RSP: 0018:ffffc900011afa60 EFLAGS: 00010093
RAX: ffffffff83bb0f41 RBX: 1ffff1102096b018 RCX: ffff888117401300
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc900011afb80 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff52000235f3c R12: 0000000000000000
R13: dffffc0000000000 R14: 1ffff92000235f54 R15: ffff888104b58000
FS:  000055556dfb2500(0000) GS:ffff8881f6e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055556db20958 CR3: 00000001217da000 CR4: 00000000003526b0
Call Trace:
 <TASK>
 tty_release+0x32f/0x11e0 drivers/tty/tty_io.c:1754
 __fput+0x208/0xa30 fs/file_table.c:447
 ____fput+0x20/0x30 fs/file_table.c:475
 task_work_run+0x1e8/0x260 kernel/task_work.c:246
 ptrace_notify+0x25a/0x290 kernel/signal.c:2419
 ptrace_report_syscall include/linux/ptrace.h:415 [inline]
 ptrace_report_syscall_exit include/linux/ptrace.h:477 [inline]
 syscall_exit_work+0x84/0x150 kernel/entry/common.c:173
 syscall_exit_to_user_mode_prepare+0x21/0x40 kernel/entry/common.c:200
 __syscall_exit_to_user_mode_work kernel/entry/common.c:205 [inline]
 syscall_exit_to_user_mode+0x15/0xb0 kernel/entry/common.c:218
 do_syscall_64+0x63/0xf0 arch/x86/entry/common.c:84
 entry_SYSCALL_64_after_hwframe+0x76/0x7e
RIP: 0033:0x7fe8d4b9e0d9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffd499d7d08 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 00007fe8d4e27da0 RCX: 00007fe8d4b9e0d9
RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
RBP: 00007fe8d4e27da0 R08: 00007fe8d4e26038 R09: 0000000000000000
R10: 000000000003fda0 R11: 0000000000000246 R12: 0000000000011987
R13: 00007fe8d4e25fac R14: 00000000000116da R15: 00007ffd499d7e10
 </TASK>
---[ end trace 0000000000000000 ]---

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/11 16:00 android16-6.12 42b03373f376 71790083 .config strace log report syz / log [disk image] [vmlinux] [kernel image] ci2-android-6-12-rust KASAN: slab-use-after-free Read in check_tty_count
2026/08/11 14:59 android16-6.12 42b03373f376 71790083 .config strace log report syz / log [disk image] [vmlinux] [kernel image] ci2-android-6-12-rust KASAN: slab-use-after-free Read in check_tty_count
* Struck through repros no longer work on HEAD.