KASAN: use-after-free Read in seq_printf

Status: upstream: reported on 2026/09/23 14:29
Reported-by: syzbot+acda12631cd6db910093@syzkaller.appspotmail.com
First crash: 49d, last: 10d
▶ ▼ Similar bugs (15)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
android-5-15 KASAN: use-after-free Read in seq_printf (2) 19 syz, C 24 1d10h 30d 0/2 upstream: reported C repro on 2026/10/12 05:38
linux-6.1 KASAN: use-after-free Read in seq_printf 19 3 19d 19d 0/3 upstream: reported on 2026/10/23 08:35
android-5-10 KASAN: use-after-free Read in seq_printf (3) 19 syz, C 64 20h20m 30d 0/2 upstream: reported C repro on 2026/10/12 19:47
android-5-10 KASAN: use-after-free Read in seq_printf 19 15 413d 521d 0/2 auto-obsoleted due to no activity on 2025/12/23 06:43
upstream KASAN: slab-out-of-bounds Read in seq_printf fs 19 5 549d 654d 0/29 auto-obsoleted due to no activity on 2025/08/09 17:54
android-6-1 KASAN: slab-out-of-bounds Read in seq_printf 19 2 417d 422d 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 301d 301d 0/2 auto-obsoleted due to no activity on 2026/04/14 16:00
android-6-1 KASAN: use-after-free Read in seq_printf origin:lts 19 syz, C 26 3d13h 48d 0/2 upstream: reported C repro on 2026/09/24 21:21
android-5-15 KASAN: use-after-free Read in seq_printf 19 1 419d 419d 0/2 auto-obsoleted due to no activity on 2025/12/17 23:30
upstream KMSAN: uninit-value in seq_printf (2) fs 7 syz, C 99 1610d 1876d 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 221d 221d 0/2 auto-obsoleted due to no activity on 2026/07/03 17:29
android-6-12 KASAN: slab-use-after-free Read in seq_printf origin:lts 19 syz, C 24 5h44m 49d 0/1 premoderation: reported C repro on 2026/09/23 06:02
upstream KMSAN: kernel-infoleak in __skb_datagram_iter net 9 68 1142d 1247d 23/29 fixed on 2023/09/28 17:51
upstream KASAN: slab-use-after-free Read in seq_printf prio:high fs 19 C error 91 13d 53d 0/29 upstream: reported C repro on 2026/09/19 02:15
linux-6.6 KASAN: slab-use-after-free Read in seq_printf 19 2 29d 78d 0/2 upstream: reported on 2026/08/25 13:48

Sample crash report:
==================================================================
BUG: KASAN: use-after-free in string_nocheck lib/vsprintf.c:642 [inline]
BUG: KASAN: use-after-free in string+0x204/0x290 lib/vsprintf.c:724
Read of size 1 at addr ffff888147228078 by task syz.2.372/5707

CPU: 0 PID: 5707 Comm: syz.2.372 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/07/2026
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
 string_nocheck lib/vsprintf.c:642 [inline]
 string+0x204/0x290 lib/vsprintf.c:724
 vsnprintf+0x10db/0x1c20 lib/vsprintf.c:2811
 seq_vprintf fs/seq_file.c:407 [inline]
 seq_printf+0x185/0x280 fs/seq_file.c:422
 show_interrupts+0x9ab/0xba0 kernel/irq/proc.c:527
 seq_read_iter+0x8af/0xc50 fs/seq_file.c:272
 proc_reg_read_iter+0x1a9/0x270 fs/proc/inode.c:300
 call_read_iter include/linux/fs.h:2173 [inline]
 new_sync_read fs/read_write.c:404 [inline]
 vfs_read+0x75e/0xd50 fs/read_write.c:485
 ksys_read+0x153/0x260 fs/read_write.c:623
 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: 0033:0x7f8575f00559
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:00007f8574115028 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 00007f8576187180 RCX: 00007f8575f00559
RDX: 0000000000002020 RSI: 0000200000001200 RDI: 0000000000000005
RBP: 00007f8575f97b50 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f8576187218 R14: 00007f8576187180 R15: 00007ffcd35394f8
 </TASK>

Allocated by task 4189:
 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_node include/linux/slab.h:630 [inline]
 __vmalloc_area_node mm/vmalloc.c:2951 [inline]
 __vmalloc_node_range+0x2dd/0x8b0 mm/vmalloc.c:3070
 __vmalloc_node mm/vmalloc.c:3120 [inline]
 vzalloc+0x75/0x80 mm/vmalloc.c:3190
 alloc_counters+0xcc/0x740 net/ipv4/netfilter/ip_tables.c:800
 copy_entries_to_user net/ipv4/netfilter/ip_tables.c:822 [inline]
 get_entries net/ipv4/netfilter/ip_tables.c:1021 [inline]
 do_ipt_get_ctl+0xa37/0x1110 net/ipv4/netfilter/ip_tables.c:1666
 nf_getsockopt+0x25e/0x280 net/netfilter/nf_sockopt.c:116
 ip_getsockopt+0x1219/0x1660 net/ipv4/ip_sockglue.c:1797
 tcp_getsockopt+0x209/0x25e0 net/ipv4/tcp.c:4325
 __sys_getsockopt+0x1b0/0x230 net/socket.c:2257
 __do_sys_getsockopt net/socket.c:2272 [inline]
 __se_sys_getsockopt net/socket.c:2269 [inline]
 __x64_sys_getsockopt+0xb1/0xc0 net/socket.c:2269
 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 ffff888147228078
 which belongs to the cache kmalloc-8 of size 8
The buggy address is located 0 bytes inside of
 8-byte region [ffff888147228078, ffff888147228080)
The buggy address belongs to the page:
page:ffffea00051c8a00 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff888147228050 pfn:0x147228
flags: 0x57ff00000000200(slab|node=1|zone=2|lastcpupid=0x7ff)
raw: 057ff00000000200 ffffea0000958640 0000000300000003 ffff888017841280
raw: ffff888147228050 0000000080660063 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, ts 8808270112, 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]
 __kmalloc+0x11d/0x340 mm/slub.c:4408
 kmalloc_array include/linux/slab.h:647 [inline]
 kcalloc include/linux/slab.h:676 [inline]
 __tty_alloc_driver+0x2d9/0x440 drivers/tty/tty_io.c:3385
 unix98_pty_init+0x41/0x6c0 drivers/tty/pty.c:883
 pty_init+0xf/0x20 drivers/tty/pty.c:944
 do_one_initcall+0x272/0x730 init/main.c:1276
 do_initcall_level+0x13d/0x1f0 init/main.c:1349
 do_initcalls+0x4b/0x90 init/main.c:1365
 kernel_init_freeable+0x3d5/0x560 init/main.c:1589
 kernel_init+0x19/0x1b0 init/main.c:1480
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
page_owner free stack trace missing

Memory state around the buggy address:
 ffff888147227f00: 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc fc
 ffff888147227f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888147228000: 00 fc fc fc fc 04 fc fc fc fc fb fc fc fc fc fb
                                                                ^
 ffff888147228080: fc fc fc fc 04 fc fc fc fc 04 fc fc fc fc 04 fc
 ffff888147228100: fc fc fc 04 fc fc fc fc 04 fc fc fc fc 04 fc fc
==================================================================

Crashes (4):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/11/01 05:39 linux-5.15.y 700e62ea909a 25a0ae84 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in seq_printf
2026/11/01 05:38 linux-5.15.y 700e62ea909a 25a0ae84 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in seq_printf
2026/10/08 10:26 linux-5.15.y a051a4bf909f 4f6a9fcf .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in seq_printf
2026/09/23 14:28 linux-5.15.y 0248c33e835e abce1216 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in seq_printf
* Struck through repros no longer work on HEAD.