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

Status: upstream: reported on 2026/07/27 23:02
Reported-by: syzbot+d5a0bec1fa88dd2ce67b@syzkaller.appspotmail.com
First crash: 23d, last: 15d
▶ ▼ 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_create_serv 22 8 8d02h 23d 0/3 upstream: reported on 2026/07/28 00:19
linux-5.15 KASAN: use-after-free Write in nfsd_create_serv 22 12 15d 23d 0/3 upstream: reported on 2026/07/27 21:42

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_create_serv+0x116/0x5c0 fs/nfsd/nfssvc.c:666
Write of size 4 at addr ffff8880255bf050 by task syz.1.28/5954

CPU: 1 PID: 5954 Comm: syz.1.28 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_create_serv+0x116/0x5c0 fs/nfsd/nfssvc.c:666
 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
RIP: 0033:0x7fa81639e019
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:00007fa8145f6028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fa816625fa0 RCX: 00007fa81639e019
RDX: 0000000000000002 RSI: 0000200000000700 RDI: 0000000000000005
RBP: 00007fa81643500c R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fa816626038 R14: 00007fa816625fa0 R15: 00007ffc04cd5de8
 </TASK>

Allocated by task 5954:
 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 5954:
 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

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
 fib6_info_release include/net/ip6_fib.h:349 [inline]
 ip6_route_add+0x10d/0x160 net/ipv6/route.c:3906
 addrconf_prefix_route net/ipv6/addrconf.c:2470 [inline]
 add_v4_addrs+0x953/0xca0 net/ipv6/addrconf.c:3268
 addrconf_gre_config net/ipv6/addrconf.c:3546 [inline]
 addrconf_init_auto_addrs+0x793/0xac0 net/ipv6/addrconf.c:3561
 addrconf_notify+0xb62/0x1010 net/ipv6/addrconf.c:3742
 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]
 __dev_notify_flags+0x1ab/0x310 net/core/dev.c:8762
 dev_change_flags+0xde/0x1a0 net/core/dev.c:8800
 do_setlink+0xb69/0x3f40 net/core/rtnetlink.c:2917
 __rtnl_newlink net/core/rtnetlink.c:3715 [inline]
 rtnl_newlink+0x1848/0x2170 net/core/rtnetlink.c:3762
 rtnetlink_rcv_msg+0x843/0xf90 net/core/rtnetlink.c:6484
 netlink_rcv_skb+0x235/0x4c0 net/netlink/af_netlink.c:2550
 netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
 netlink_unicast+0x7b1/0x930 net/netlink/af_netlink.c:1346
 netlink_sendmsg+0x8d0/0xbf0 net/netlink/af_netlink.c:1899
 sock_sendmsg_nosec net/socket.c:730 [inline]
 __sock_sendmsg net/socket.c:745 [inline]
 __sys_sendto+0x4a9/0x6b0 net/socket.c:2201
 __do_sys_sendto net/socket.c:2213 [inline]
 __se_sys_sendto net/socket.c:2209 [inline]
 __x64_sys_sendto+0xde/0xf0 net/socket.c:2209
 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 ffff8880255bf000
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 80 bytes inside of
 freed 512-byte region [ffff8880255bf000, ffff8880255bf200)

The buggy address belongs to the physical page:
page:ffffea0000956f00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x255bc
head:ffffea0000956f00 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 ffffea00017b7000 dead000000000002
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 1629, tgid 1629 (kworker/u4:7), ts 12849363926, 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:
 ffff8880255bef00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff8880255bef80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8880255bf000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                 ^
 ffff8880255bf080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8880255bf100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (6):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/05 00:12 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_create_serv
2026/08/04 23:05 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_create_serv
2026/08/04 21:02 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_create_serv
2026/07/27 23:23 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_create_serv
2026/07/27 23:22 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_create_serv
2026/07/27 23:01 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_create_serv
* Struck through repros no longer work on HEAD.