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

Status: upstream: reported on 2026/07/27 23:12
Reported-by: syzbot+c0081e36d956ba121a48@syzkaller.appspotmail.com
First crash: 23d, last: 20m
▶ ▼ Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.1 KASAN: use-after-free Read in nfsd_svc 19 23 1d15h 24d 0/3 upstream: reported on 2026/07/27 07:18
linux-5.15 KASAN: use-after-free Write in nfsd_svc 22 3 15d 24d 0/3 upstream: reported on 2026/07/27 22:56

Sample crash report:
svc: failed to register nfsdv3 RPC service (errno 111).
svc: failed to register nfsaclv3 RPC service (errno 111).
==================================================================
BUG: KASAN: slab-use-after-free in nfsd_svc+0x99a/0xab0 fs/nfsd/nfssvc.c:818
Read of size 4 at addr ffff888026055054 by task syz.3.980/8748

CPU: 0 PID: 8748 Comm: syz.3.980 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
 nfsd_svc+0x99a/0xab0 fs/nfsd/nfssvc.c:818
 write_threads+0x393/0x510 fs/nfsd/nfsctl.c:417
 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
RIP: 0033:0x7f672579e0d9
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:00007f67266c6028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f6725a25fa0 RCX: 00007f672579e0d9
RDX: 0000000000000001 RSI: 0000200000000900 RDI: 0000000000000004
RBP: 00007f6725835024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f6725a26038 R14: 00007f6725a25fa0 R15: 00007ffd79da0018
 </TASK>

Allocated by task 8748:
 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
 nfsd_svc+0x183/0xab0 fs/nfsd/nfssvc.c:801
 write_threads+0x393/0x510 fs/nfsd/nfsctl.c:417
 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 8748:
 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]
 nfsd_svc+0x762/0xab0 fs/nfsd/nfssvc.c:816
 write_threads+0x393/0x510 fs/nfsd/nfsctl.c:417
 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

Last potentially related work creation:
 kasan_save_stack+0x3e/0x60 mm/kasan/common.c:46
 __kasan_record_aux_stack+0xaf/0xc0 mm/kasan/generic.c:492
 __call_rcu_common kernel/rcu/tree.c:2721 [inline]
 call_rcu+0x153/0x900 kernel/rcu/tree.c:2837
 in_dev_put include/linux/inetdevice.h:279 [inline]
 inetdev_destroy net/ipv4/devinet.c:334 [inline]
 inetdev_event+0x847/0x1610 net/ipv4/devinet.c:1636
 notifier_call_chain+0x18f/0x380 kernel/notifier.c:93
 call_netdevice_notifiers_extack net/core/dev.c:2077 [inline]
 call_netdevice_notifiers net/core/dev.c:2091 [inline]
 unregister_netdevice_many_notify+0x1037/0x1910 net/core/dev.c:11137
 unregister_netdevice_many net/core/dev.c:11193 [inline]
 unregister_netdevice_queue+0x2e9/0x330 net/core/dev.c:11073
 unregister_netdevice include/linux/netdevice.h:3141 [inline]
 __tun_detach+0xdb2/0x1580 drivers/net/tun.c:685
 tun_detach drivers/net/tun.c:701 [inline]
 tun_chr_close+0x10d/0x1c0 drivers/net/tun.c:3514
 __fput+0x221/0x940 fs/file_table.c:418
 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

Second to last potentially related work creation:
 kasan_save_stack+0x3e/0x60 mm/kasan/common.c:46
 __kasan_record_aux_stack+0xaf/0xc0 mm/kasan/generic.c:492
 kvfree_call_rcu+0xee/0x780 kernel/rcu/tree.c:3452
 drop_sysctl_table+0x394/0x540 fs/proc/proc_sysctl.c:1515
 drop_sysctl_table+0x3ab/0x540 fs/proc/proc_sysctl.c:1518
 unregister_sysctl_table+0x41/0x60 fs/proc/proc_sysctl.c:1536
 neigh_sysctl_unregister+0x78/0xa0 net/core/neighbour.c:3899
 devinet_sysctl_unregister net/ipv4/devinet.c:2685 [inline]
 inetdev_destroy net/ipv4/devinet.c:330 [inline]
 inetdev_event+0x7d9/0x1610 net/ipv4/devinet.c:1636
 notifier_call_chain+0x18f/0x380 kernel/notifier.c:93
 call_netdevice_notifiers_extack net/core/dev.c:2077 [inline]
 call_netdevice_notifiers net/core/dev.c:2091 [inline]
 unregister_netdevice_many_notify+0x1037/0x1910 net/core/dev.c:11137
 unregister_netdevice_many net/core/dev.c:11193 [inline]
 unregister_netdevice_queue+0x2e9/0x330 net/core/dev.c:11073
 unregister_netdevice include/linux/netdevice.h:3141 [inline]
 __tun_detach+0xdb2/0x1580 drivers/net/tun.c:685
 tun_detach drivers/net/tun.c:701 [inline]
 tun_chr_close+0x10d/0x1c0 drivers/net/tun.c:3514
 __fput+0x221/0x940 fs/file_table.c:418
 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

The buggy address belongs to the object at ffff888026055000
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 84 bytes inside of
 freed 512-byte region [ffff888026055000, ffff888026055200)

The buggy address belongs to the physical page:
page:ffffea0000981500 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x26054
head:ffffea0000981500 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 1686, tgid 1686 (kworker/u4:5), ts 12752882486, 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:
 ffff888026054f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888026054f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888026055000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                 ^
 ffff888026055080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888026055100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (4):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/20 22:42 linux-6.6.y c610b395b0a5 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Read in nfsd_svc
2026/08/20 22:42 linux-6.6.y c610b395b0a5 1e72964b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Read in nfsd_svc
2026/08/05 01:23 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 Read in nfsd_svc
2026/07/27 23:11 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 Read in nfsd_svc
* Struck through repros no longer work on HEAD.