KASAN: use-after-free Write in nfsd_create_serv

Status: upstream: reported on 2026/07/27 21:42
Reported-by: syzbot+087fc6d8c1e2f78f5966@syzkaller.appspotmail.com
First crash: 82d, last: 12d
▶ ▼ 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 12d 81d 0/3 upstream: reported on 2026/07/28 00:19
linux-6.6 KASAN: slab-use-after-free Write in nfsd_create_serv 22 9 29d 81d 0/2 upstream: reported on 2026/07/27 23:02

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_create_serv+0x11b/0x700 fs/nfsd/nfssvc.c:662
Write of size 4 at addr ffff88802a5c0c50 by task syz.3.198/4925

CPU: 0 PID: 4925 Comm: syz.3.198 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/16/2026
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_create_serv+0x11b/0x700 fs/nfsd/nfssvc.c:662
 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
RIP: 0033:0x7f0c8519d199
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:00007f0c833d4028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f0c85425090 RCX: 00007f0c8519d199
RDX: 0000000000000002 RSI: 0000200000000640 RDI: 0000000000000004
RBP: 00007f0c852340b8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f0c85425128 R14: 00007f0c85425090 R15: 00007ffe389a2688
 </TASK>

Allocated by task 4921:
 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:485
 svc_create_pooled+0x62f/0x810 net/sunrpc/svc.c:573
 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 4921:
 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 ffff88802a5c0c00
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 80 bytes inside of
 512-byte region [ffff88802a5c0c00, ffff88802a5c0e00)
The buggy address belongs to the page:
page:ffffea0000a97000 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x2a5c0
head:ffffea0000a97000 order:2 compound_mapcount:0 compound_pincount:0
flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000010200 0000000000000000 0000000300000001 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 1, ts 16910246814, 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_page_interleave+0x24/0x1e0 mm/mempolicy.c:2031
 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]
 device_private_init drivers/base/core.c:3256 [inline]
 device_add+0xb2/0x1050 drivers/base/core.c:3306
 cdev_device_add+0x19d/0x340 fs/char_dev.c:549
 i2cdev_attach_adapter+0x2de/0x4c0 drivers/i2c/i2c-dev.c:677
 notifier_call_chain kernel/notifier.c:83 [inline]
 blocking_notifier_call_chain+0x103/0x1b0 kernel/notifier.c:318
 device_add+0x943/0x1050 drivers/base/core.c:3390
 i2c_register_adapter+0x4c4/0x12c0 drivers/i2c/i2c-core-base.c:1566
 vidtv_bridge_i2c_register_adap drivers/media/test-drivers/vidtv/vidtv_bridge.c:309 [inline]
 vidtv_bridge_dvb_init drivers/media/test-drivers/vidtv/vidtv_bridge.c:420 [inline]
 vidtv_bridge_probe+0x299/0xf30 drivers/media/test-drivers/vidtv/vidtv_bridge.c:510
 platform_probe+0x137/0x1c0 drivers/base/platform.c:1391
 call_driver_probe drivers/base/dd.c:-1 [inline]
 really_probe+0x276/0xc70 drivers/base/dd.c:595
 __driver_probe_device+0x1f5/0x390 drivers/base/dd.c:775
page_owner free stack trace missing

Memory state around the buggy address:
 ffff88802a5c0b00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88802a5c0b80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88802a5c0c00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                 ^
 ffff88802a5c0c80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88802a5c0d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (23):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/10/05 20:40 linux-5.15.y a051a4bf909f af63e995 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_create_serv
2026/10/05 20:40 linux-5.15.y a051a4bf909f af63e995 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_create_serv
2026/10/05 07:50 linux-5.15.y a051a4bf909f 57bbd979 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_create_serv
2026/10/05 07:48 linux-5.15.y a051a4bf909f 57bbd979 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_create_serv
2026/10/04 22:15 linux-5.15.y a051a4bf909f 57bbd979 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_create_serv
2026/09/18 01:25 linux-5.15.y 0248c33e835e 8d7d05f1 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_create_serv
2026/09/17 19:36 linux-5.15.y 0248c33e835e 8d7d05f1 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_create_serv
2026/09/15 06:46 linux-5.15.y 0248c33e835e 81a27d1a .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_create_serv
2026/09/15 06:45 linux-5.15.y 0248c33e835e 81a27d1a .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_create_serv
2026/09/15 01:15 linux-5.15.y 0248c33e835e 81a27d1a .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_create_serv
2026/08/25 02:43 linux-5.15.y 945fa863f02c 614e416a .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_create_serv
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_create_serv
2026/08/03 20:38 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_create_serv
2026/08/03 20:38 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_create_serv
2026/08/03 19:22 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_create_serv
2026/08/03 19:21 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_create_serv
2026/07/28 00:00 linux-5.15.y 674f684f7c61 aae9036b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_create_serv
2026/07/28 00:00 linux-5.15.y 674f684f7c61 aae9036b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_create_serv
2026/07/27 23:09 linux-5.15.y 674f684f7c61 aae9036b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_create_serv
2026/07/27 22:37 linux-5.15.y 674f684f7c61 aae9036b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_create_serv
2026/07/27 21:46 linux-5.15.y 674f684f7c61 aae9036b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_create_serv
2026/07/27 21:42 linux-5.15.y 674f684f7c61 aae9036b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_create_serv
2026/07/27 21:42 linux-5.15.y 674f684f7c61 aae9036b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Write in nfsd_create_serv
* Struck through repros no longer work on HEAD.