syzbot


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

Status: moderation: reported on 2025/10/07 11:49
Subsystems: fs
[Documentation on labels]
Reported-by: syzbot+3366add91c4b8d9822cf@syzkaller.appspotmail.com
First crash: 180d, last: 7d08h
✨ AI Jobs (3)
ID Workflow Result Correct Bug Created Started Finished Revision Error
4237d129-e104-4eb5-8412-1d82bdc08159 moderation Actionable: ✅  Confident: ✅  KASAN: slab-use-after-free Read in seq_printf 2026/02/06 12:22 2026/02/06 12:27 2026/02/06 12:35 97745f52f5b9361548048f53f0b3b51b9313fedf
487d6af1-3a00-4d7e-8875-b3e486e5a7e1 moderation 💥 KASAN: slab-use-after-free Read in seq_printf 2026/02/06 07:04 2026/02/06 09:45 2026/02/06 09:56 9b618abc0cd923b36c7a5ebc58a21174112d8f70 tool grepper failed: error: failed to run ["git" "grep" "--extended-regexp" "--line-number" "--show-function" "-C1" "--no-color" "->phys ="]: exit status 129 error: unknown switch `>' usage: git grep [<options>] [-e] <pattern> [<rev>...] [[--] <path>...] --[no-]cached search in index instead of in the work tree --no-index find in contents not managed by git --index opposite of --no-index --[no-]untracked search in both tracked and untracked files --[no-]exclude-standard ignore files specified via '.gitignore' --[no-]recurse-submodules recursively search in each submodule -v, --[no-]invert-match show non-matching lines -i, --[no-]ignore-case case insensitive matching -w, --[no-]word-regexp match patterns only at word boundaries -a, --[no-]text process binary files as text -I don't match patterns in binary files --[no-]textconv process binary files with textconv filters -r, --[no-]recursive search in subdirectories (default) --max-depth <n> descend at most <n> levels -E, --[no-]extended-regexp use extended POSIX regular expressions -G, --[no-]basic-regexp use basic POSIX regular expressions (default) -F, --[no-]fixed-strings interpret patterns as fixed strings -P, --[no-]perl-regexp use Perl-compatible regular expressions -n, --[no-]line-number show line numbers --[no-]column show column number of first match -h don't show filenames -H show filenames --[no-]full-name show filenames relative to top directory -l, --[no-]files-with-matches show only filenames instead of matching lines --[no-]name-only synonym for --files-with-matches -L, --[no-]files-without-match show only the names of files without match -z, --[no-]null print NUL after filenames -o, --[no-]only-matching show only matching parts of a line -c, --[no-]count show the number of matches instead of matching lines --[no-]color[=<when>] highlight matches --[no-]break print empty line between matches from different files --[no-]heading show filename only once above matches from same file -C, --[no-]context <n> show <n> context lines before and after matches -B, --before-context <n> show <n> context lines before matches -A, --after-context <n> show <n> context lines after matches --[no-]threads <n> use <n> worker threads -NUM shortcut for -C NUM -p, --[no-]show-function show a line with the function name before matches -W, --[no-]function-context show the surrounding function -f <file> read patterns from file -e <pattern> match <pattern> --and combine patterns specified with -e --or --not ( ) -q, --[no-]quiet indicate hit with exit status without output --[no-]all-match show only matches from files that match all patterns -O, --[no-]open-files-in-pager[=<pager>] show matching files in the pager --[no-]ext-grep allow calling of grep(1) (ignored by this build) -m, --[no-]max-count <n> maximum number of results per file args: map[Expression:->phys =]
d54d6933-0060-4a4e-a71e-b7c4f79b4a3f moderation Actionable: ✅  Confident: ✅  KASAN: slab-use-after-free Read in seq_printf 2026/01/15 18:55 2026/01/15 18:55 2026/01/15 19:24 a9d6a79219801d2130df3b1a792c57f0e5428e9f
Similar bugs (7)
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 325d 430d 0/29 auto-obsoleted due to no activity on 2025/08/09 17:54
upstream KMSAN: uninit-value in seq_printf (2) fs 7 C 99 1386d 1652d 0/29 auto-closed as invalid on 2022/09/30 02:43
android-5-10 KASAN: use-after-free Read in seq_printf 19 15 189d 296d 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 918d 1023d 23/29 fixed on 2023/09/28 17:51
android-6-1 KASAN: slab-out-of-bounds Read in seq_printf 19 2 193d 198d 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 77d 77d 0/2 premoderation: reported on 2026/01/14 15:56
android-5-15 KASAN: use-after-free Read in seq_printf 19 1 194d 194d 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:655 [inline]
BUG: KASAN: slab-use-after-free in string+0x231/0x2b0 lib/vsprintf.c:737
Read of size 1 at addr ffff88807b740220 by task syz.3.6614/31373

CPU: 1 UID: 0 PID: 31373 Comm: syz.3.6614 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xba/0x230 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 string_nocheck lib/vsprintf.c:655 [inline]
 string+0x231/0x2b0 lib/vsprintf.c:737
 vsnprintf+0x739/0xee0 lib/vsprintf.c:2948
 seq_vprintf fs/seq_file.c:392 [inline]
 seq_printf+0x188/0x290 fs/seq_file.c:407
 input_devices_seq_show+0x145/0x640 drivers/input/input.c:1099
 seq_read_iter+0x9bb/0xe10 fs/seq_file.c:273
 seq_read+0x367/0x480 fs/seq_file.c:163
 pde_read fs/proc/inode.c:308 [inline]
 proc_reg_read+0x1e9/0x2e0 fs/proc/inode.c:320
 vfs_read+0x20c/0xa70 fs/read_write.c:572
 ksys_read+0x150/0x270 fs/read_write.c:717
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f6dd239c799
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:00007f6dd3206028 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 00007f6dd2615fa0 RCX: 00007f6dd239c799
RDX: 0000000000002020 RSI: 00002000000028c0 RDI: 000000000000000a
RBP: 00007f6dd2432c99 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f6dd2616038 R14: 00007f6dd2615fa0 R15: 00007f6dd273fa48
 </TASK>

Allocated by task 3569:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __do_kmalloc_node mm/slub.c:5260 [inline]
 __kmalloc_node_track_caller_noprof+0x4db/0x7b0 mm/slub.c:5368
 kmalloc_reserve net/core/skbuff.c:635 [inline]
 pskb_expand_head+0x228/0x1320 net/core/skbuff.c:2315
 __skb_cow include/linux/skbuff.h:3854 [inline]
 skb_cow_head include/linux/skbuff.h:3888 [inline]
 batadv_skb_head_push+0x169/0x200 net/batman-adv/mesh-interface.c:71
 batadv_send_skb_packet+0xc8/0x690 net/batman-adv/send.c:81
 batadv_iv_ogm_send_to_if net/batman-adv/bat_iv_ogm.c:391 [inline]
 batadv_iv_ogm_emit net/batman-adv/bat_iv_ogm.c:419 [inline]
 batadv_iv_send_outstanding_bat_ogm_packet+0x631/0x7e0 net/batman-adv/bat_iv_ogm.c:1700
 process_one_work kernel/workqueue.c:3276 [inline]
 process_scheduled_works+0xb6e/0x18c0 kernel/workqueue.c:3359
 worker_thread+0xa53/0xfc0 kernel/workqueue.c:3440
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Freed by task 3569:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2685 [inline]
 slab_free mm/slub.c:6165 [inline]
 kfree+0x1c1/0x630 mm/slub.c:6483
 skb_kfree_head net/core/skbuff.c:1089 [inline]
 skb_free_head net/core/skbuff.c:1101 [inline]
 skb_release_data+0x6f0/0x940 net/core/skbuff.c:1128
 skb_release_all net/core/skbuff.c:1203 [inline]
 __kfree_skb+0x5d/0x210 net/core/skbuff.c:1217
 kfree_skb_reason include/linux/skbuff.h:1322 [inline]
 __netif_receive_skb_core+0x2c10/0x31a0 net/core/dev.c:6138
 __netif_receive_skb_one_core net/core/dev.c:6162 [inline]
 __netif_receive_skb net/core/dev.c:6277 [inline]
 process_backlog+0x76d/0x1950 net/core/dev.c:6628
 __napi_poll+0xae/0x340 net/core/dev.c:7692
 napi_poll net/core/dev.c:7755 [inline]
 net_rx_action+0x627/0xf70 net/core/dev.c:7912
 handle_softirqs+0x22a/0x870 kernel/softirq.c:622
 do_softirq+0x76/0xd0 kernel/softirq.c:523
 __local_bh_enable_ip+0xf8/0x130 kernel/softirq.c:450
 local_bh_enable include/linux/bottom_half.h:33 [inline]
 rcu_read_unlock_bh include/linux/rcupdate.h:924 [inline]
 __dev_queue_xmit+0x1e78/0x3890 net/core/dev.c:4873
 dev_queue_xmit include/linux/netdevice.h:3385 [inline]
 batadv_send_skb_packet+0x418/0x690 net/batman-adv/send.c:100
 batadv_iv_ogm_send_to_if net/batman-adv/bat_iv_ogm.c:391 [inline]
 batadv_iv_ogm_emit net/batman-adv/bat_iv_ogm.c:419 [inline]
 batadv_iv_send_outstanding_bat_ogm_packet+0x631/0x7e0 net/batman-adv/bat_iv_ogm.c:1700
 process_one_work kernel/workqueue.c:3276 [inline]
 process_scheduled_works+0xb6e/0x18c0 kernel/workqueue.c:3359
 worker_thread+0xa53/0xfc0 kernel/workqueue.c:3440
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

The buggy address belongs to the object at ffff88807b740000
 which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 544 bytes inside of
 freed 1024-byte region [ffff88807b740000, ffff88807b740400)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff88807b746800 pfn:0x7b740
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0xfff00000000240(workingset|head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000240 ffff88813fea5dc0 ffffea00009ef010 ffffea0000af0a10
raw: ffff88807b746800 000000080010000e 00000000f5000000 0000000000000000
head: 00fff00000000240 ffff88813fea5dc0 ffffea00009ef010 ffffea0000af0a10
head: ffff88807b746800 000000080010000e 00000000f5000000 0000000000000000
head: 00fff00000000003 ffffea0001edd001 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000008
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd2820(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 49, tgid 49 (kworker/u8:3), ts 1036267831810, free_ts 1036182398552
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x231/0x280 mm/page_alloc.c:1889
 prep_new_page mm/page_alloc.c:1897 [inline]
 get_page_from_freelist+0x24dc/0x2580 mm/page_alloc.c:3962
 __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5250
 alloc_slab_page mm/slub.c:3292 [inline]
 allocate_slab+0x77/0x660 mm/slub.c:3481
 new_slab mm/slub.c:3539 [inline]
 refill_objects+0x331/0x3c0 mm/slub.c:7175
 refill_sheaf mm/slub.c:2812 [inline]
 __pcs_replace_empty_main+0x2e6/0x730 mm/slub.c:4615
 alloc_from_pcs mm/slub.c:4717 [inline]
 slab_alloc_node mm/slub.c:4851 [inline]
 __do_kmalloc_node mm/slub.c:5259 [inline]
 __kmalloc_noprof+0x474/0x760 mm/slub.c:5272
 kmalloc_noprof include/linux/slab.h:954 [inline]
 kzalloc_noprof include/linux/slab.h:1188 [inline]
 ieee802_11_parse_elems_full+0x159/0x2ab0 net/mac80211/parse.c:1051
 ieee802_11_parse_elems net/mac80211/ieee80211_i.h:2480 [inline]
 ieee80211_inform_bss+0x161/0x1160 net/mac80211/scan.c:79
 rdev_inform_bss net/wireless/rdev-ops.h:418 [inline]
 cfg80211_inform_single_bss_data+0xd08/0x1b70 net/wireless/scan.c:2372
 cfg80211_inform_bss_data+0x266/0x3c40 net/wireless/scan.c:3226
 cfg80211_inform_bss_frame_data+0x3c7/0x760 net/wireless/scan.c:3317
 ieee80211_bss_info_update+0x794/0xa40 net/mac80211/scan.c:230
 ieee80211_rx_bss_info net/mac80211/ibss.c:1094 [inline]
 ieee80211_rx_mgmt_probe_beacon net/mac80211/ibss.c:1575 [inline]
 ieee80211_ibss_rx_queued_mgmt+0x1901/0x2cd0 net/mac80211/ibss.c:1602
 ieee80211_iface_process_skb net/mac80211/iface.c:1748 [inline]
 ieee80211_iface_work+0x84e/0x1340 net/mac80211/iface.c:1802
 cfg80211_wiphy_work+0x2ab/0x4a0 net/wireless/core.c:440
page last free pid 18137 tgid 18127 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 __free_pages_prepare mm/page_alloc.c:1433 [inline]
 __free_frozen_pages+0xc2b/0xdb0 mm/page_alloc.c:2978
 __slab_free+0x263/0x2b0 mm/slub.c:5573
 qlink_free mm/kasan/quarantine.c:163 [inline]
 qlist_free_all+0x97/0x100 mm/kasan/quarantine.c:179
 kasan_quarantine_reduce+0x148/0x160 mm/kasan/quarantine.c:286
 __kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:350
 kasan_slab_alloc include/linux/kasan.h:253 [inline]
 slab_post_alloc_hook mm/slub.c:4538 [inline]
 slab_alloc_node mm/slub.c:4866 [inline]
 kmem_cache_alloc_noprof+0x2bc/0x650 mm/slub.c:4873
 __proc_create+0x535/0xa60 fs/proc/generic.c:452
 proc_create_reg+0x8b/0x110 fs/proc/generic.c:578
 proc_create_net_data+0x98/0x1d0 fs/proc/proc_net.c:120
 rxrpc_init_net+0x6ff/0x8c0 net/rxrpc/net_ns.c:79
 ops_init+0x35c/0x5c0 net/core/net_namespace.c:137
 setup_net+0x118/0x340 net/core/net_namespace.c:446
 copy_net_ns+0x50e/0x730 net/core/net_namespace.c:581
 create_new_namespaces+0x3e7/0x6a0 kernel/nsproxy.c:130
 unshare_nsproxy_namespaces+0x11a/0x160 kernel/nsproxy.c:226
 ksys_unshare+0x51d/0x930 kernel/fork.c:3173

Memory state around the buggy address:
 ffff88807b740100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88807b740180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88807b740200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                               ^
 ffff88807b740280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88807b740300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (6):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/03/25 10:29 upstream bbeb83d3182a 35e4ff71 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce KASAN: slab-use-after-free Read in seq_printf
2026/01/08 06:25 upstream f0b9d8eb98df d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce KASAN: slab-use-after-free Read in seq_printf
2025/12/18 22:23 upstream ea1013c15392 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root KASAN: slab-use-after-free Read in seq_printf
2025/10/26 18:17 upstream 72761a7e3122 c0460fcd .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce KASAN: slab-use-after-free Read in seq_printf
2025/10/03 11:42 upstream e406d57be7bd 49379ee0 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce KASAN: slab-use-after-free Read in seq_printf
2026/01/01 10:13 upstream 9528d5c091c5 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-386 KASAN: slab-use-after-free Read in seq_printf
* Struck through repros no longer work on HEAD.