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: 82d, last: 30d
▶ ▼ 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 19 13d 82d 0/3 upstream: reported on 2026/07/28 00:19
linux-5.15 KASAN: use-after-free Write in nfsd_create_serv 22 23 12d 82d 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 ffff88805f04fc50 by task syz.1.47/6015

CPU: 0 PID: 6015 Comm: syz.1.47 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: 0033:0x7f9c9199e159
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:00007f9c927c6028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f9c91c26090 RCX: 00007f9c9199e159
RDX: 0000000000000002 RSI: 0000200000000280 RDI: 0000000000000004
RBP: 00007f9c91a3506b R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f9c91c26128 R14: 00007f9c91c26090 R15: 00007ffcf68a14f8
 </TASK>

Allocated by task 6012:
 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+0x60/0xbb0 net/sunrpc/svc.c:520
 svc_create_pooled+0x66a/0x7e0 net/sunrpc/svc.c:618
 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 6012:
 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 ffff88805f04fc00
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 80 bytes inside of
 freed 512-byte region [ffff88805f04fc00, ffff88805f04fe00)

The buggy address belongs to the physical page:
page:ffffea00017c1300 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x5f04c
head:ffffea00017c1300 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 ffffea00017c1700 0000000000000002
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 2968, tgid 2968 (kworker/u4:11), ts 81097477259, free_ts 81046711679
 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
 __do_kmalloc_node mm/slab_common.c:1006 [inline]
 __kmalloc+0xa7/0x240 mm/slab_common.c:1020
 kmalloc include/linux/slab.h:604 [inline]
 kzalloc include/linux/slab.h:721 [inline]
 fib6_info_alloc+0x30/0xf0 net/ipv6/ip6_fib.c:155
 ip6_route_info_create+0x455/0x1260 net/ipv6/route.c:3805
 ip6_route_add+0x28/0x160 net/ipv6/route.c:3901
 addrconf_add_mroute net/ipv6/addrconf.c:2534 [inline]
 addrconf_add_dev+0x29c/0x3b0 net/ipv6/addrconf.c:2552
 addrconf_dev_config net/ipv6/addrconf.c:3481 [inline]
 addrconf_init_auto_addrs+0x611/0xac0 net/ipv6/addrconf.c:3569
 addrconf_notify+0xb62/0x1010 net/ipv6/addrconf.c:3742
 notifier_call_chain+0x18f/0x380 kernel/notifier.c:93
 netdev_state_change+0xe4/0x170 net/core/dev.c:1421
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1182 [inline]
 free_unref_page_prepare+0x7d7/0x8f0 mm/page_alloc.c:2366
 free_unref_page+0x32/0x2e0 mm/page_alloc.c:2459
 __stack_depot_save+0x587/0x660 lib/stackdepot.c:443
 kasan_save_stack mm/kasan/common.c:47 [inline]
 kasan_set_track+0x5f/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+0xf8/0x290 mm/slub.c:3852
 vma_lock_free kernel/fork.c:473 [inline]
 __vm_area_free+0xe4/0x110 kernel/fork.c:529
 rcu_do_batch kernel/rcu/tree.c:2194 [inline]
 rcu_core+0x9c1/0x17f0 kernel/rcu/tree.c:2467
 handle_softirqs+0x27d/0x820 kernel/softirq.c:578
 do_softirq+0xfa/0x1a0 kernel/softirq.c:479
 __local_bh_enable_ip+0x184/0x1c0 kernel/softirq.c:406
 br_device_event+0x5cd/0x920 net/bridge/br.c:94
 notifier_call_chain+0x18f/0x380 kernel/notifier.c:93
 netdev_state_change+0xe4/0x170 net/core/dev.c:1421

Memory state around the buggy address:
 ffff88805f04fb00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88805f04fb80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88805f04fc00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                 ^
 ffff88805f04fc80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88805f04fd00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (9):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/18 01:24 linux-6.6.y 79643295eba1 8d7d05f1 .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
2026/09/18 01:15 linux-6.6.y 79643295eba1 8d7d05f1 .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
2026/09/15 00:48 linux-6.6.y 79643295eba1 81a27d1a .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
2026/08/05 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.