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

Status: upstream: reported on 2026/08/25 13:48
Reported-by: syzbot+ee2d36546061d54fecdd@syzkaller.appspotmail.com
First crash: 3d10h, last: 3d10h
▶ ▼ Similar bugs (10)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KASAN: slab-out-of-bounds Read in seq_printf fs 19 5 474d 579d 0/29 auto-obsoleted due to no activity on 2025/08/09 17:54
upstream KASAN: slab-use-after-free Read in seq_printf prio:high fs 19 28 3d18h 325d 0/29 moderation: reported on 2025/10/07 11:49
android-5-15 KASAN: use-after-free Read in seq_printf (2) 19 2 2d22h 2d22h 0/2 premoderation: reported on 2026/08/26 02:30
upstream KMSAN: uninit-value in seq_printf (2) fs 7 syz, C 99 1535d 1801d 0/29 auto-closed as invalid on 2022/09/30 02:43
android-6-1 KASAN: slab-out-of-bounds Read in seq_printf (2) 17 1 146d 146d 0/2 auto-obsoleted due to no activity on 2026/07/03 17:29
android-5-10 KASAN: use-after-free Read in seq_printf 19 15 338d 446d 0/2 auto-obsoleted due to no activity on 2025/12/23 06:43
upstream KMSAN: kernel-infoleak in __skb_datagram_iter net 9 68 1067d 1172d 23/29 fixed on 2023/09/28 17:51
android-6-1 KASAN: slab-out-of-bounds Read in seq_printf 19 2 342d 347d 0/2 auto-obsoleted due to no activity on 2025/12/19 00:57
android-5-10 KASAN: use-after-free Read in seq_printf (2) 19 1 226d 226d 0/2 auto-obsoleted due to no activity on 2026/04/14 16:00
android-5-15 KASAN: use-after-free Read in seq_printf 19 1 344d 344d 0/2 auto-obsoleted due to no activity on 2025/12/17 23:30

Sample crash report:
==================================================================
BUG: KASAN: slab-use-after-free in string_nocheck lib/vsprintf.c:645 [inline]
BUG: KASAN: slab-use-after-free in string+0x204/0x290 lib/vsprintf.c:727
Read of size 1 at addr ffff88801efe5d70 by task syz.8.4829/20870

CPU: 1 PID: 20870 Comm: syz.8.4829 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
 string_nocheck lib/vsprintf.c:645 [inline]
 string+0x204/0x290 lib/vsprintf.c:727
 vsnprintf+0xf72/0x1ba0 lib/vsprintf.c:2823
 seq_vprintf fs/seq_file.c:391 [inline]
 seq_printf+0x189/0x290 fs/seq_file.c:406
 show_interrupts+0x95e/0xb20 kernel/irq/proc.c:527
 seq_read_iter+0x8b3/0xc50 fs/seq_file.c:272
 proc_reg_read_iter+0x1af/0x280 fs/proc/inode.c:305
 call_read_iter include/linux/fs.h:2012 [inline]
 new_sync_read fs/read_write.c:389 [inline]
 vfs_read+0x486/0x990 fs/read_write.c:470
 ksys_read+0x151/0x260 fs/read_write.c:613
 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: 0033:0x7f7f7db9e0d9
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:00007f7f7e997028 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 00007f7f7de25fa0 RCX: 00007f7f7db9e0d9
RDX: 00000000000003f7 RSI: 0000200000000340 RDI: 0000000000000003
RBP: 00007f7f7dc35024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f7f7de26038 R14: 00007f7f7de25fa0 R15: 00007ffe357eaaa8
 </TASK>

Allocated by task 9074:
 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
 kasan_kmalloc include/linux/kasan.h:198 [inline]
 __do_kmalloc_node mm/slab_common.c:1007 [inline]
 __kmalloc_node+0xb6/0x240 mm/slab_common.c:1014
 kmalloc_node include/linux/slab.h:620 [inline]
 __vmalloc_area_node mm/vmalloc.c:3175 [inline]
 __vmalloc_node_range+0x598/0x1320 mm/vmalloc.c:3370
 __vmalloc_node mm/vmalloc.c:3435 [inline]
 vzalloc+0x79/0x90 mm/vmalloc.c:3508
 __do_replace+0xb4/0x9b0 net/ipv6/netfilter/ip6_tables.c:1061
 do_replace net/ipv6/netfilter/ip6_tables.c:1156 [inline]
 do_ip6t_set_ctl+0xb41/0xe10 net/ipv6/netfilter/ip6_tables.c:1641
 nf_setsockopt+0x263/0x280 net/netfilter/nf_sockopt.c:101
 do_sock_setsockopt+0x175/0x1a0 net/socket.c:2322
 __sys_setsockopt net/socket.c:2345 [inline]
 __do_sys_setsockopt net/socket.c:2354 [inline]
 __se_sys_setsockopt net/socket.c:2351 [inline]
 __x64_sys_setsockopt+0x182/0x200 net/socket.c:2351
 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 9074:
 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
 vfree+0x2b0/0x340 mm/vmalloc.c:2904
 __do_replace+0x878/0x9b0 net/ipv6/netfilter/ip6_tables.c:1105
 do_replace net/ipv6/netfilter/ip6_tables.c:1156 [inline]
 do_ip6t_set_ctl+0xb41/0xe10 net/ipv6/netfilter/ip6_tables.c:1641
 nf_setsockopt+0x263/0x280 net/netfilter/nf_sockopt.c:101
 do_sock_setsockopt+0x175/0x1a0 net/socket.c:2322
 __sys_setsockopt net/socket.c:2345 [inline]
 __do_sys_setsockopt net/socket.c:2354 [inline]
 __se_sys_setsockopt net/socket.c:2351 [inline]
 __x64_sys_setsockopt+0x182/0x200 net/socket.c:2351
 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 ffff88801efe5d70
 which belongs to the cache kmalloc-8 of size 8
The buggy address is located 0 bytes inside of
 freed 8-byte region [ffff88801efe5d70, ffff88801efe5d78)

The buggy address belongs to the physical page:
page:ffffea00007bf940 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1efe5
flags: 0xfff00000000800(slab|node=0|zone=1|lastcpupid=0x7ff)
page_type: 0xffffffff()
raw: 00fff00000000800 ffff888017c41280 dead000000000100 dead000000000122
raw: 0000000000000000 0000000000660066 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x12cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY), pid 1, tgid 1 (swapper/0), ts 8263198755, free_ts 8260149840
 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_page_interleave+0x24/0x1e0 mm/mempolicy.c:2118
 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_node_track_caller+0xa4/0x230 mm/slab_common.c:1027
 kstrdup+0x3b/0x80 mm/util.c:62
 __kernfs_new_node+0xaa/0x7f0 fs/kernfs/dir.c:620
 kernfs_new_node+0x14c/0x260 fs/kernfs/dir.c:700
 kernfs_create_link+0xa7/0x200 fs/kernfs/symlink.c:39
 sysfs_do_create_link_sd+0x83/0x110 fs/sysfs/symlink.c:44
 device_create_sys_dev_entry+0x123/0x180 drivers/base/core.c:3511
 device_add+0x7c3/0xc40 drivers/base/core.c:3655
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
 vfree+0x1a7/0x340 mm/vmalloc.c:2899
 delayed_vfree_work+0x55/0x80 mm/vmalloc.c:2819
 process_one_work kernel/workqueue.c:2657 [inline]
 process_scheduled_works+0xa60/0x1600 kernel/workqueue.c:2734
 worker_thread+0xa5e/0xfe0 kernel/workqueue.c:2815
 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

Memory state around the buggy address:
 ffff88801efe5c00: fc 06 fc fc fc fc 06 fc fc fc fc 06 fc fc fc fc
 ffff88801efe5c80: 06 fc fc fc fc 03 fc fc fc fc fa fc fc fc fc 00
>ffff88801efe5d00: fc fc fc fc 00 fc fc fc fc fa fc fc fc fc fa fc
                                                             ^
 ffff88801efe5d80: fc fc fc fa fc fc fc fc 05 fc fc fc fc 03 fc fc
 ffff88801efe5e00: fc fc 07 fc fc fc fc fa fc fc fc fc fa fc fc fc
==================================================================

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/25 13:47 linux-6.6.y dc6160265ffc a9a1fc32 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Read in seq_printf
* Struck through repros no longer work on HEAD.