KASAN: slab-use-after-free Write in nfsd_shutdown_threads

Status: upstream: reported on 2026/07/27 20:29
Reported-by: syzbot+4f4ec3e0810f614aee7b@syzkaller.appspotmail.com
First crash: 16d, last: 1d10h
▶ ▼ Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-5.15 KASAN: use-after-free Write in nfsd_shutdown_threads origin:lts-only 22 syz, C 513 19h07m 17d 0/3 upstream: reported C repro on 2026/07/27 08:38
linux-6.1 KASAN: use-after-free Write in nfsd_shutdown_threads 22 28 1d06h 17d 0/3 upstream: reported on 2026/07/27 08:48

Sample crash report:
==================================================================
BUG: KASAN: slab-use-after-free in instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
BUG: KASAN: slab-use-after-free in atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:252 [inline]
BUG: KASAN: slab-use-after-free in __refcount_add include/linux/refcount.h:193 [inline]
BUG: KASAN: slab-use-after-free in __refcount_inc include/linux/refcount.h:250 [inline]
BUG: KASAN: slab-use-after-free in refcount_inc include/linux/refcount.h:267 [inline]
BUG: KASAN: slab-use-after-free in kref_get include/linux/kref.h:45 [inline]
BUG: KASAN: slab-use-after-free in svc_get include/linux/sunrpc/svc.h:109 [inline]
BUG: KASAN: slab-use-after-free in nfsd_shutdown_threads+0x8d/0x1a0 fs/nfsd/nfssvc.c:645
Write of size 4 at addr ffff88802fdc6c50 by task syz-executor/5775

CPU: 0 PID: 5775 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+0x18c/0x250 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:364 [inline]
 print_report+0xa8/0x210 mm/kasan/report.c:468
 kasan_report+0x117/0x150 mm/kasan/report.c:581
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x241/0x290 mm/kasan/generic.c:187
 instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
 atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:252 [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:109 [inline]
 nfsd_shutdown_threads+0x8d/0x1a0 fs/nfsd/nfssvc.c:645
 nfsd_umount+0x42/0xc0 fs/nfsd/nfsctl.c:1464
 deactivate_locked_super+0x97/0x100 fs/super.c:481
 cleanup_mnt+0x3d7/0x460 fs/namespace.c:1259
 task_work_run+0x1d4/0x260 kernel/task_work.c:245
 resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
 exit_to_user_mode_loop+0xe6/0x110 kernel/entry/common.c:177
 exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:210
 __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
 syscall_exit_to_user_mode+0x1a/0x50 kernel/entry/common.c:302
 do_syscall_64+0x61/0xb0 arch/x86/entry/common.c:82
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f496259f317
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:00007fff13642bd8 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
RAX: 0000000000000000 RBX: 00007f4962634474 RCX: 00007f496259f317
RDX: 0000000000000000 RSI: 0000000000000009 RDI: 00007fff13642c90
RBP: 00007fff13642c90 R08: 00007fff13643c90 R09: 00000000ffffffff
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fff13643d20
R13: 00007f4962634474 R14: 0000000000018752 R15: 00007fff13643d60
 </TASK>

Allocated by task 6287:
 kasan_save_stack mm/kasan/common.c:46 [inline]
 kasan_set_track+0x4e/0x70 mm/kasan/common.c:53
 ____kasan_kmalloc mm/kasan/common.c:375 [inline]
 __kasan_kmalloc+0x8f/0xa0 mm/kasan/common.c:384
 kmalloc include/linux/slab.h:600 [inline]
 kzalloc include/linux/slab.h:721 [inline]
 __svc_create+0x60/0xa20 net/sunrpc/svc.c:464
 svc_create_pooled+0x66a/0x7e0 net/sunrpc/svc.c:556
 nfsd_create_serv+0x29f/0x5c0 fs/nfsd/nfssvc.c:672
 __write_ports_addfd fs/nfsd/nfsctl.c:712 [inline]
 __write_ports fs/nfsd/nfsctl.c:788 [inline]
 write_ports+0x698/0xfa0 fs/nfsd/nfsctl.c:844
 nfsctl_transaction_write+0x10c/0x150 fs/nfsd/nfsctl.c:113
 vfs_write+0x299/0x9a0 fs/read_write.c:582
 ksys_write+0x151/0x260 fs/read_write.c:637
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

Freed by task 6287:
 kasan_save_stack mm/kasan/common.c:46 [inline]
 kasan_set_track+0x4e/0x70 mm/kasan/common.c:53
 kasan_save_free_info+0x28/0x40 mm/kasan/generic.c:522
 ____kasan_slab_free+0x126/0x1f0 mm/kasan/common.c:237
 kasan_slab_free include/linux/kasan.h:164 [inline]
 slab_free_hook mm/slub.c:1811 [inline]
 slab_free_freelist_hook+0x130/0x1a0 mm/slub.c:1837
 slab_free mm/slub.c:3830 [inline]
 __kmem_cache_free+0xba/0x1f0 mm/slub.c:3843
 kref_put include/linux/kref.h:65 [inline]
 svc_put include/linux/sunrpc/svc.h:124 [inline]
 __write_ports_addfd fs/nfsd/nfsctl.c:724 [inline]
 __write_ports fs/nfsd/nfsctl.c:788 [inline]
 write_ports+0xb1a/0xfa0 fs/nfsd/nfsctl.c:844
 nfsctl_transaction_write+0x10c/0x150 fs/nfsd/nfsctl.c:113
 vfs_write+0x299/0x9a0 fs/read_write.c:582
 ksys_write+0x151/0x260 fs/read_write.c:637
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

The buggy address belongs to the object at ffff88802fdc6c00
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 80 bytes inside of
 freed 512-byte region [ffff88802fdc6c00, ffff88802fdc6e00)

The buggy address belongs to the physical page:
page:ffffea0000bf7100 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x2fdc4
head:ffffea0000bf7100 order:2 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0xfff00000000840(slab|head|node=0|zone=1|lastcpupid=0x7ff)
page_type: 0xffffffff()
raw: 00fff00000000840 ffff888017c41c80 dead000000000100 dead000000000122
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 4317, tgid 4317 (kworker/u4:2), ts 23222838635, free_ts 0
 set_page_owner include/linux/page_owner.h:31 [inline]
 post_alloc_hook+0x1c1/0x200 mm/page_alloc.c:1582
 prep_new_page mm/page_alloc.c:1589 [inline]
 get_page_from_freelist+0x2181/0x22a0 mm/page_alloc.c:3221
 __alloc_pages+0x1f0/0x460 mm/page_alloc.c:4501
 alloc_slab_page+0x5d/0x180 mm/slub.c:1881
 allocate_slab mm/slub.c:2028 [inline]
 new_slab+0x87/0x2d0 mm/slub.c:2081
 ___slab_alloc+0xc5c/0x12f0 mm/slub.c:3253
 __slab_alloc mm/slub.c:3339 [inline]
 __slab_alloc_node mm/slub.c:3392 [inline]
 slab_alloc_node mm/slub.c:3485 [inline]
 __kmem_cache_alloc_node+0x11f/0x250 mm/slub.c:3534
 kmalloc_trace+0x2a/0xe0 mm/slab_common.c:1098
 kmalloc include/linux/slab.h:600 [inline]
 kzalloc include/linux/slab.h:721 [inline]
 alloc_bprm+0x56/0x9a0 fs/exec.c:1538
 kernel_execve+0x98/0x980 fs/exec.c:2023
 call_usermodehelper_exec_async+0x20b/0x350 kernel/umh.c:110
 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
page_owner free stack trace missing

Memory state around the buggy address:
 ffff88802fdc6b00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88802fdc6b80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88802fdc6c00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                 ^
 ffff88802fdc6c80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88802fdc6d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (8):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/12 06:54 linux-6.6.y d27334b2888c f8d35649 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Write in nfsd_shutdown_threads
2026/08/04 22:21 linux-6.6.y aa0e49877a2e d4abbeac .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Write in nfsd_shutdown_threads
2026/08/04 22:17 linux-6.6.y aa0e49877a2e d4abbeac .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Write in nfsd_shutdown_threads
2026/07/28 12:45 linux-6.6.y c5596480c50e 45ae1df4 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Write in nfsd_shutdown_threads
2026/07/27 23:13 linux-6.6.y c5596480c50e aae9036b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Write in nfsd_shutdown_threads
2026/07/27 23:07 linux-6.6.y c5596480c50e aae9036b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Write in nfsd_shutdown_threads
2026/07/27 20:29 linux-6.6.y c5596480c50e aae9036b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Write in nfsd_shutdown_threads
2026/07/27 20:28 linux-6.6.y c5596480c50e aae9036b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Write in nfsd_shutdown_threads
* Struck through repros no longer work on HEAD.