KASAN: use-after-free Write in nfsd_shutdown_threads

Status: upstream: reported C repro on 2026/07/27 08:38
Bug presence: origin:lts-only
[Documentation on labels]
Reported-by: syzbot+ae02940eff06b915b7ab@syzkaller.appspotmail.com
First crash: 13d, last: 20h25m
▶ ▼ Bug presence (2)
Date Name Commit Repro Result
2026/07/30 linux-5.15.y (ToT) 6e2fd6534337 C [report] KASAN: use-after-free Write in nfsd_shutdown_threads
2026/07/30 upstream (ToT) 11028ab62899 C Didn't crash
▶ ▼ Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.1 KASAN: use-after-free Write in nfsd_shutdown_threads 22 22 2d18h 13d 0/3 upstream: reported on 2026/07/27 08:48
linux-6.6 KASAN: slab-use-after-free Write in nfsd_shutdown_threads 22 7 4d18h 12d 0/2 upstream: reported on 2026/07/27 20:29

Sample crash report:
==================================================================
BUG: KASAN: use-after-free in instrument_atomic_read_write include/linux/instrumented.h:101 [inline]
BUG: KASAN: use-after-free in atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:111 [inline]
BUG: KASAN: use-after-free in __refcount_add include/linux/refcount.h:193 [inline]
BUG: KASAN: use-after-free in __refcount_inc include/linux/refcount.h:250 [inline]
BUG: KASAN: use-after-free in refcount_inc include/linux/refcount.h:267 [inline]
BUG: KASAN: use-after-free in kref_get include/linux/kref.h:45 [inline]
BUG: KASAN: use-after-free in svc_get include/linux/sunrpc/svc.h:108 [inline]
BUG: KASAN: use-after-free in nfsd_shutdown_threads+0x89/0x1a0 fs/nfsd/nfssvc.c:641
Write of size 4 at addr ffff88801fc9cc50 by task syz-executor/4339

CPU: 1 PID: 4339 Comm: syz-executor Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
 print_address_description+0x60/0x2d0 mm/kasan/report.c:248
 __kasan_report mm/kasan/report.c:434 [inline]
 kasan_report+0xdf/0x130 mm/kasan/report.c:451
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x235/0x290 mm/kasan/generic.c:189
 instrument_atomic_read_write include/linux/instrumented.h:101 [inline]
 atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:111 [inline]
 __refcount_add include/linux/refcount.h:193 [inline]
 __refcount_inc include/linux/refcount.h:250 [inline]
 refcount_inc include/linux/refcount.h:267 [inline]
 kref_get include/linux/kref.h:45 [inline]
 svc_get include/linux/sunrpc/svc.h:108 [inline]
 nfsd_shutdown_threads+0x89/0x1a0 fs/nfsd/nfssvc.c:641
 nfsd_umount+0x3e/0xc0 fs/nfsd/nfsctl.c:1411
 deactivate_locked_super+0x93/0xf0 fs/super.c:335
 cleanup_mnt+0x426/0x4d0 fs/namespace.c:1148
 task_work_run+0x125/0x1a0 kernel/task_work.c:188
 get_signal+0x123e/0x12e0 kernel/signal.c:2681
 arch_do_signal_or_restart+0xe6/0x12a0 arch/x86/kernel/signal.c:867
 handle_signal_work kernel/entry/common.c:154 [inline]
 exit_to_user_mode_loop+0x9e/0x130 kernel/entry/common.c:178
 exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:214
 __syscall_exit_to_user_mode_work kernel/entry/common.c:296 [inline]
 syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:307
 do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f7070c7f317
Code: a2 c7 05 dc 43 25 00 00 00 00 00 eb 96 e8 e1 12 00 00 90 31 f6 e9 09 00 00 00 66 0f 1f 84 00 00 00 00 00 b8 a6 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 01 c3 48 c7 c2 e8 ff ff ff f7 d8 64 89 02 b8
RSP: 002b:00007ffdcda303f8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
RAX: 0000000000000000 RBX: 00007f7070d14474 RCX: 00007f7070c7f317
RDX: 0000000000000000 RSI: 0000000000000009 RDI: 00007ffdcda304b0
RBP: 00007ffdcda304b0 R08: 00007ffdcda314b0 R09: 00000000ffffffff
R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffdcda31540
R13: 00007f7070d14474 R14: 000000000000fdf3 R15: 00007ffdcda31580
 </TASK>

Allocated by task 4418:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track mm/kasan/common.c:46 [inline]
 set_alloc_info mm/kasan/common.c:434 [inline]
 ____kasan_kmalloc mm/kasan/common.c:513 [inline]
 __kasan_kmalloc+0xaf/0xe0 mm/kasan/common.c:522
 kmalloc include/linux/slab.h:607 [inline]
 kzalloc include/linux/slab.h:738 [inline]
 __svc_create+0x60/0x9d0 net/sunrpc/svc.c:458
 svc_create_pooled+0x62f/0x810 net/sunrpc/svc.c:546
 nfsd_create_serv+0x2f9/0x700 fs/nfsd/nfssvc.c:668
 nfsd_svc+0x132/0x9e0 fs/nfsd/nfssvc.c:798
 write_threads+0x2ea/0x350 fs/nfsd/nfsctl.c:426
 nfsctl_transaction_write+0x105/0x150 fs/nfsd/nfsctl.c:114
 vfs_write+0x304/0xd70 fs/read_write.c:592
 ksys_write+0x153/0x260 fs/read_write.c:647
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0

Freed by task 4418:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track+0x4b/0x70 mm/kasan/common.c:46
 kasan_set_free_info+0x1f/0x40 mm/kasan/generic.c:360
 ____kasan_slab_free+0xd5/0x110 mm/kasan/common.c:366
 kasan_slab_free include/linux/kasan.h:230 [inline]
 slab_free_hook mm/slub.c:1710 [inline]
 slab_free_freelist_hook+0xec/0x170 mm/slub.c:1736
 slab_free mm/slub.c:3504 [inline]
 kfree+0xef/0x2a0 mm/slub.c:4564
 kref_put include/linux/kref.h:65 [inline]
 svc_put include/linux/sunrpc/svc.h:123 [inline]
 nfsd_svc+0x7cf/0x9e0 fs/nfsd/nfssvc.c:821
 write_threads+0x2ea/0x350 fs/nfsd/nfsctl.c:426
 nfsctl_transaction_write+0x105/0x150 fs/nfsd/nfsctl.c:114
 vfs_write+0x304/0xd70 fs/read_write.c:592
 ksys_write+0x153/0x260 fs/read_write.c:647
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0

The buggy address belongs to the object at ffff88801fc9cc00
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 80 bytes inside of
 512-byte region [ffff88801fc9cc00, ffff88801fc9ce00)
The buggy address belongs to the page:
page:ffffea00007f2700 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1fc9c
head:ffffea00007f2700 order:2 compound_mapcount:0 compound_pincount:0
flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000010200 dead000000000100 dead000000000122 ffff888016c41c80
raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 2, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 922, ts 5911659135, free_ts 0
 prep_new_page mm/page_alloc.c:2426 [inline]
 get_page_from_freelist+0x24f6/0x2670 mm/page_alloc.c:4192
 __alloc_pages+0x1ee/0x480 mm/page_alloc.c:5501
 alloc_slab_page mm/slub.c:1780 [inline]
 allocate_slab mm/slub.c:1917 [inline]
 new_slab+0xc0/0x4b0 mm/slub.c:1980
 ___slab_alloc+0x807/0xdd0 mm/slub.c:3013
 __slab_alloc mm/slub.c:3100 [inline]
 slab_alloc_node mm/slub.c:3191 [inline]
 slab_alloc mm/slub.c:3233 [inline]
 kmem_cache_alloc_trace+0xf9/0x290 mm/slub.c:3250
 kmalloc include/linux/slab.h:607 [inline]
 kzalloc include/linux/slab.h:738 [inline]
 alloc_bprm+0x56/0x690 fs/exec.c:1516
 kernel_execve+0x49/0x8e0 fs/exec.c:1978
 call_usermodehelper_exec_async+0x207/0x350 kernel/umh.c:112
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
page_owner free stack trace missing

Memory state around the buggy address:
 ffff88801fc9cb00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88801fc9cb80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88801fc9cc00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                 ^
 ffff88801fc9cc80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88801fc9cd00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (484):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/08 20:32 linux-5.15.y aabd761612db 5d63f80b .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/06 11:17 linux-5.15.y 6e2fd6534337 cd5b1963 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/04 09:08 linux-5.15.y 6e2fd6534337 9451e17e .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/01 01:01 linux-5.15.y 6e2fd6534337 7664cf44 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/07/31 09:00 linux-5.15.y 6e2fd6534337 aaffb173 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/07/31 07:10 linux-5.15.y 6e2fd6534337 aaffb173 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/07/29 11:13 linux-5.15.y 674f684f7c61 19622d9d .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/08 08:13 linux-5.15.y aabd761612db 5d63f80b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/08 07:27 linux-5.15.y aabd761612db 5d63f80b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/07 13:29 linux-5.15.y aabd761612db e4ef95d6 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/06 22:36 linux-5.15.y 9c7634c60784 c38879ea .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/06 21:31 linux-5.15.y 9c7634c60784 c38879ea .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/06 17:44 linux-5.15.y 6e2fd6534337 c38879ea .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/05 23:25 linux-5.15.y 6e2fd6534337 cd5b1963 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/05 22:11 linux-5.15.y 6e2fd6534337 cd5b1963 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/05 07:25 linux-5.15.y 6e2fd6534337 52aa2820 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/05 07:15 linux-5.15.y 6e2fd6534337 52aa2820 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/05 01:50 linux-5.15.y 6e2fd6534337 d4abbeac .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/05 01:24 linux-5.15.y 6e2fd6534337 d4abbeac .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/05 00:17 linux-5.15.y 6e2fd6534337 d4abbeac .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/04 23:31 linux-5.15.y 6e2fd6534337 d4abbeac .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/04 22:30 linux-5.15.y 6e2fd6534337 d4abbeac .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/04 21:30 linux-5.15.y 6e2fd6534337 d4abbeac .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/04 21:30 linux-5.15.y 6e2fd6534337 d4abbeac .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/04 20:18 linux-5.15.y 6e2fd6534337 d4abbeac .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/04 19:31 linux-5.15.y 6e2fd6534337 d4abbeac .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/04 18:46 linux-5.15.y 6e2fd6534337 d4abbeac .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/04 18:18 linux-5.15.y 6e2fd6534337 d4abbeac .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/04 16:53 linux-5.15.y 6e2fd6534337 d4abbeac .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/04 11:02 linux-5.15.y 6e2fd6534337 9451e17e .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/04 05:14 linux-5.15.y 6e2fd6534337 9451e17e .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/04 02:18 linux-5.15.y 6e2fd6534337 9451e17e .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/03 19:57 linux-5.15.y 6e2fd6534337 6b7c9f71 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/03 19:43 linux-5.15.y 6e2fd6534337 6b7c9f71 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/03 19:23 linux-5.15.y 6e2fd6534337 6b7c9f71 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/03 19:10 linux-5.15.y 6e2fd6534337 6b7c9f71 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/03 19:05 linux-5.15.y 6e2fd6534337 6b7c9f71 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/03 14:18 linux-5.15.y 6e2fd6534337 6b7c9f71 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/02 12:54 linux-5.15.y 6e2fd6534337 e611ffe1 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/08/01 05:59 linux-5.15.y 6e2fd6534337 e611ffe1 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/07/31 16:58 linux-5.15.y 6e2fd6534337 7664cf44 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/07/31 15:54 linux-5.15.y 6e2fd6534337 7664cf44 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/07/30 22:21 linux-5.15.y 6e2fd6534337 aaffb173 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/07/30 21:19 linux-5.15.y 6e2fd6534337 aaffb173 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/07/30 15:44 linux-5.15.y 6e2fd6534337 2377cd3d .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/07/30 10:51 linux-5.15.y 674f684f7c61 2377cd3d .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/07/30 10:48 linux-5.15.y 674f684f7c61 2377cd3d .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/07/29 19:34 linux-5.15.y 674f684f7c61 6ef5c1e2 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/07/29 17:47 linux-5.15.y 674f684f7c61 6ef5c1e2 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
2026/07/27 08:37 linux-5.15.y 674f684f7c61 492bab15 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_shutdown_threads
* Struck through repros no longer work on HEAD.