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

Status: upstream: reported C repro on 2025/11/03 02:12
Bug presence: origin:upstream
Labels: missing-backport
[Documentation on labels]
Reported-by: syzbot+c403668aa48e478a3408@syzkaller.appspotmail.com
First crash: 268d, last: 220d
Fix bisection: failed (error log, bisect log)
  
▶ ▼ Bug presence (3)
Date Name Commit Repro Result
2025/12/21 linux-6.6.y (ToT) 5fa4793a2d2d C [report] KASAN: slab-use-after-free Write in recv_work
2025/11/05 upstream (ToT) dc77806cf3b4 C [report] KASAN: slab-use-after-free Write in recv_work
2025/12/21 upstream (ToT) 9094662f6707 C Didn't crash
▶ ▼ Similar bugs (5)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KASAN: slab-use-after-free Write in recv_work (3) nbd 22 syz, C 6 241d 268d 29/29 fixed on 2026/01/07 12:29
upstream KASAN: slab-use-after-free Write in recv_work (2) nbd 22 syz, C 16 346d 442d 29/29 fixed on 2025/09/04 16:57
upstream KASAN: slab-use-after-free Write in recv_work nbd 22 10 452d 593d 28/29 fixed on 2025/05/06 15:33
upstream KASAN: use-after-free Read in recv_work nbd 19 1 2007d 2003d 0/29 auto-closed as invalid on 2021/03/30 16:37
upstream KASAN: use-after-free Read in recv_work (2) nbd 19 1 1644d 1639d 0/29 auto-closed as invalid on 2022/05/27 07:10
▶ ▼ Fix bisection attempts (6)
Created Duration User Patch Repo Result
2026/05/17 01:15 14m fix candidate upstream error job log
2026/03/24 07:51 1m fix candidate upstream error job log
2026/02/21 09:17 0m fix candidate upstream error job log
2026/01/21 23:56 1m fix candidate upstream error job log
2026/01/21 17:57 0m bisect fix linux-6.6.y error job log
2025/12/05 10:09 1h55m bisect fix linux-6.6.y OK (0) job log log

Sample crash report:
block nbd0: Receive control failed (result -32)
block nbd0: shutting down sockets
==================================================================
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_dec include/linux/atomic/atomic-instrumented.h:592 [inline]
BUG: KASAN: slab-use-after-free in recv_work+0x1b03/0x1bf0 drivers/block/nbd.c:916
Write of size 4 at addr ffff88807724a278 by task kworker/u5:2/5875

CPU: 0 PID: 5875 Comm: kworker/u5:2 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Workqueue: nbd0-recv recv_work
Call Trace:
 <TASK>
 dump_stack_lvl+0x16c/0x230 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:364 [inline]
 print_report+0xac/0x220 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+0x288/0x290 mm/kasan/generic.c:187
 instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
 atomic_dec include/linux/atomic/atomic-instrumented.h:592 [inline]
 recv_work+0x1b03/0x1bf0 drivers/block/nbd.c:916
 process_one_work kernel/workqueue.c:2634 [inline]
 process_scheduled_works+0xa45/0x15b0 kernel/workqueue.c:2711
 worker_thread+0xa55/0xfc0 kernel/workqueue.c:2792
 kthread+0x2fa/0x390 kernel/kthread.c:388
 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
 </TASK>

Allocated by task 5947:
 kasan_save_stack mm/kasan/common.c:45 [inline]
 kasan_set_track+0x4e/0x70 mm/kasan/common.c:52
 ____kasan_kmalloc mm/kasan/common.c:374 [inline]
 __kasan_kmalloc+0x8f/0xa0 mm/kasan/common.c:383
 kmalloc include/linux/slab.h:600 [inline]
 kzalloc include/linux/slab.h:721 [inline]
 nbd_alloc_and_init_config+0x88/0x260 drivers/block/nbd.c:1587
 nbd_genl_connect+0x9d8/0x18e0 drivers/block/nbd.c:2051
 genl_family_rcv_msg_doit+0x209/0x2f0 net/netlink/genetlink.c:971
 genl_family_rcv_msg net/netlink/genetlink.c:1051 [inline]
 genl_rcv_msg+0x60b/0x790 net/netlink/genetlink.c:1066
 netlink_rcv_skb+0x216/0x480 net/netlink/af_netlink.c:2545
 genl_rcv+0x28/0x40 net/netlink/genetlink.c:1075
 netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
 netlink_unicast+0x751/0x8d0 net/netlink/af_netlink.c:1346
 netlink_sendmsg+0x8c1/0xbe0 net/netlink/af_netlink.c:1894
 sock_sendmsg_nosec net/socket.c:730 [inline]
 __sock_sendmsg net/socket.c:745 [inline]
 ____sys_sendmsg+0x5bf/0x950 net/socket.c:2595
 ___sys_sendmsg+0x220/0x290 net/socket.c:2649
 __sys_sendmsg net/socket.c:2678 [inline]
 __do_sys_sendmsg net/socket.c:2687 [inline]
 __se_sys_sendmsg+0x1a5/0x270 net/socket.c:2685
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

Freed by task 5875:
 kasan_save_stack mm/kasan/common.c:45 [inline]
 kasan_set_track+0x4e/0x70 mm/kasan/common.c:52
 kasan_save_free_info+0x2e/0x50 mm/kasan/generic.c:522
 ____kasan_slab_free+0x126/0x1e0 mm/kasan/common.c:236
 kasan_slab_free include/linux/kasan.h:164 [inline]
 slab_free_hook mm/slub.c:1811 [inline]
 slab_free_freelist_hook+0x130/0x1b0 mm/slub.c:1837
 slab_free mm/slub.c:3830 [inline]
 __kmem_cache_free+0xba/0x1f0 mm/slub.c:3843
 nbd_config_put+0x57e/0x770 drivers/block/nbd.c:1375
 recv_work+0x1aed/0x1bf0 drivers/block/nbd.c:915
 process_one_work kernel/workqueue.c:2634 [inline]
 process_scheduled_works+0xa45/0x15b0 kernel/workqueue.c:2711
 worker_thread+0xa55/0xfc0 kernel/workqueue.c:2792
 kthread+0x2fa/0x390 kernel/kthread.c:388
 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293

The buggy address belongs to the object at ffff88807724a200
 which belongs to the cache kmalloc-256 of size 256
The buggy address is located 120 bytes inside of
 freed 256-byte region [ffff88807724a200, ffff88807724a300)

The buggy address belongs to the physical page:
page:ffffea0001dc9280 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x7724a
head:ffffea0001dc9280 order:1 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0xfff00000000840(slab|head|node=0|zone=1|lastcpupid=0x7ff)
page_type: 0xffffffff()
raw: 00fff00000000840 ffff888017841b40 dead000000000122 0000000000000000
raw: 0000000000000000 0000000080100010 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 1, migratetype Unmovable, gfp_mask 0x1d20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 5901, tgid 5901 (syz-executor), ts 103788179082, free_ts 103771414875
 set_page_owner include/linux/page_owner.h:31 [inline]
 post_alloc_hook+0x1cd/0x210 mm/page_alloc.c:1554
 prep_new_page mm/page_alloc.c:1561 [inline]
 get_page_from_freelist+0x195c/0x19f0 mm/page_alloc.c:3191
 __alloc_pages+0x1e3/0x460 mm/page_alloc.c:4457
 alloc_slab_page+0x5d/0x170 mm/slub.c:1881
 allocate_slab mm/slub.c:2028 [inline]
 new_slab+0x87/0x2e0 mm/slub.c:2081
 ___slab_alloc+0xc6d/0x1300 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+0x1a2/0x260 mm/slub.c:3534
 __do_kmalloc_node mm/slab_common.c:1006 [inline]
 __kmalloc_node_track_caller+0xa2/0x230 mm/slab_common.c:1027
 kmemdup+0x2b/0x70 mm/util.c:131
 kmemdup include/linux/fortify-string.h:779 [inline]
 ip6t_register_table+0x28a/0x7b0 net/ipv6/netfilter/ip6_tables.c:1776
 ip6table_mangle_table_init+0x41/0x60 net/ipv6/netfilter/ip6table_mangle.c:84
 xt_find_table_lock+0x306/0x3e0 net/netfilter/x_tables.c:1259
 xt_request_find_table_lock+0x26/0x100 net/netfilter/x_tables.c:1284
 get_info net/ipv6/netfilter/ip6_tables.c:979 [inline]
 do_ip6t_get_ctl+0x729/0x1150 net/ipv6/netfilter/ip6_tables.c:1668
 nf_getsockopt+0x262/0x280 net/netfilter/nf_sockopt.c:116
 ipv6_getsockopt+0x216/0x2c0 net/ipv6/ipv6_sockglue.c:1499
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1154 [inline]
 free_unref_page_prepare+0x7ce/0x8e0 mm/page_alloc.c:2336
 free_unref_page+0x32/0x2e0 mm/page_alloc.c:2429
 discard_slab mm/slub.c:2127 [inline]
 __unfreeze_partials+0x1cf/0x210 mm/slub.c:2667
 put_cpu_partial+0x17c/0x250 mm/slub.c:2743
 __slab_free+0x31d/0x410 mm/slub.c:3700
 qlink_free mm/kasan/quarantine.c:166 [inline]
 qlist_free_all+0x75/0xe0 mm/kasan/quarantine.c:185
 kasan_quarantine_reduce+0x143/0x160 mm/kasan/quarantine.c:292
 __kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:305
 kasan_slab_alloc include/linux/kasan.h:188 [inline]
 slab_post_alloc_hook+0x6e/0x4d0 mm/slab.h:767
 slab_alloc_node mm/slub.c:3495 [inline]
 slab_alloc mm/slub.c:3503 [inline]
 __kmem_cache_alloc_lru mm/slub.c:3510 [inline]
 kmem_cache_alloc+0x11e/0x2e0 mm/slub.c:3519
 getname_kernel+0x5a/0x2f0 fs/namei.c:228
 kern_path+0x1d/0x50 fs/namei.c:2617
 tomoyo_mount_acl security/tomoyo/mount.c:136 [inline]
 tomoyo_mount_permission+0x774/0x970 security/tomoyo/mount.c:237
 security_sb_mount+0x87/0xc0 security/security.c:1375
 path_mount+0xbc/0xfe0 fs/namespace.c:3655
 do_mount fs/namespace.c:3726 [inline]
 __do_sys_mount fs/namespace.c:3935 [inline]
 __se_sys_mount+0x2da/0x3c0 fs/namespace.c:3912

Memory state around the buggy address:
 ffff88807724a100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88807724a180: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88807724a200: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                                ^
 ffff88807724a280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88807724a300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/11/03 10:13 linux-6.6.y 0a805b6ea8cd 2c50b6a9 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Write in recv_work
2025/11/03 02:11 linux-6.6.y 0a805b6ea8cd 2c50b6a9 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Write in recv_work
* Struck through repros no longer work on HEAD.