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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: 53d, last: 30d
▶ ▼ Similar bugs (6)
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 198d 303d 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 1259d 1526d 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 63d 170d 0/2 premoderation: reported on 2025/06/08 22:35
upstream KMSAN: kernel-infoleak in __skb_datagram_iter net 9 68 791d 896d 23/29 fixed on 2023/09/28 17:51
android-6-1 KASAN: slab-out-of-bounds Read in seq_printf 19 2 67d 71d 0/2 premoderation: reported on 2025/09/15 09:58
android-5-15 KASAN: use-after-free Read in seq_printf 19 1 68d 68d 0/2 premoderation: reported on 2025/09/18 23:28

Sample crash report:
==================================================================
BUG: KASAN: slab-use-after-free in string_nocheck lib/vsprintf.c:653 [inline]
BUG: KASAN: slab-use-after-free in string+0x231/0x2b0 lib/vsprintf.c:735
Read of size 1 at addr ffff88802301a220 by task syz.1.1593/12207

CPU: 1 UID: 0 PID: 12207 Comm: syz.1.1593 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xca/0x240 mm/kasan/report.c:482
 kasan_report+0x118/0x150 mm/kasan/report.c:595
 string_nocheck lib/vsprintf.c:653 [inline]
 string+0x231/0x2b0 lib/vsprintf.c:735
 vsnprintf+0x739/0xf00 lib/vsprintf.c:2926
 seq_vprintf fs/seq_file.c:391 [inline]
 seq_printf+0x178/0x270 fs/seq_file.c:406
 input_devices_seq_show+0x145/0x640 drivers/input/input.c:1099
 seq_read_iter+0x4ef/0xe20 fs/seq_file.c:230
 seq_read+0x369/0x480 fs/seq_file.c:162
 pde_read fs/proc/inode.c:308 [inline]
 proc_reg_read+0x1e9/0x2e0 fs/proc/inode.c:320
 do_loop_readv_writev fs/read_write.c:847 [inline]
 vfs_readv+0x5aa/0x850 fs/read_write.c:1020
 do_preadv fs/read_write.c:1132 [inline]
 __do_sys_preadv fs/read_write.c:1179 [inline]
 __se_sys_preadv fs/read_write.c:1174 [inline]
 __x64_sys_preadv+0x197/0x2a0 fs/read_write.c:1174
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f2b8198efc9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f2b82820038 EFLAGS: 00000246 ORIG_RAX: 0000000000000127
RAX: ffffffffffffffda RBX: 00007f2b81be5fa0 RCX: 00007f2b8198efc9
RDX: 0000000000000001 RSI: 0000200000000980 RDI: 0000000000000003
RBP: 00007f2b81a11f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000401 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f2b81be6038 R14: 00007f2b81be5fa0 R15: 00007f2b81d0fa28
 </TASK>

Allocated by task 1006:
 kasan_save_stack mm/kasan/common.c:56 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:77
 poison_kmalloc_redzone mm/kasan/common.c:400 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:417
 kasan_kmalloc include/linux/kasan.h:262 [inline]
 __do_kmalloc_node mm/slub.c:5642 [inline]
 __kmalloc_noprof+0x411/0x7f0 mm/slub.c:5654
 kmalloc_noprof include/linux/slab.h:961 [inline]
 kzalloc_noprof include/linux/slab.h:1094 [inline]
 ieee802_11_parse_elems_full+0x152/0x2ab0 net/mac80211/parse.c:1011
 ieee802_11_parse_elems_crc net/mac80211/ieee80211_i.h:2470 [inline]
 ieee802_11_parse_elems net/mac80211/ieee80211_i.h:2477 [inline]
 ieee80211_rx_mgmt_probe_beacon net/mac80211/ibss.c:1569 [inline]
 ieee80211_ibss_rx_queued_mgmt+0x47a/0x2af0 net/mac80211/ibss.c:1600
 ieee80211_iface_process_skb net/mac80211/iface.c:1694 [inline]
 ieee80211_iface_work+0x85f/0x12d0 net/mac80211/iface.c:1748
 cfg80211_wiphy_work+0x2bb/0x470 net/wireless/core.c:435
 process_one_work kernel/workqueue.c:3263 [inline]
 process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3346
 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3427
 kthread+0x711/0x8a0 kernel/kthread.c:463
 ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Freed by task 1006:
 kasan_save_stack mm/kasan/common.c:56 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:77
 __kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:587
 kasan_save_free_info mm/kasan/kasan.h:406 [inline]
 poison_slab_object mm/kasan/common.c:252 [inline]
 __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:284
 kasan_slab_free include/linux/kasan.h:234 [inline]
 slab_free_hook mm/slub.c:2539 [inline]
 slab_free mm/slub.c:6630 [inline]
 kfree+0x19a/0x6d0 mm/slub.c:6837
 ieee80211_rx_mgmt_probe_beacon net/mac80211/ibss.c:1574 [inline]
 ieee80211_ibss_rx_queued_mgmt+0x1207/0x2af0 net/mac80211/ibss.c:1600
 ieee80211_iface_process_skb net/mac80211/iface.c:1694 [inline]
 ieee80211_iface_work+0x85f/0x12d0 net/mac80211/iface.c:1748
 cfg80211_wiphy_work+0x2bb/0x470 net/wireless/core.c:435
 process_one_work kernel/workqueue.c:3263 [inline]
 process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3346
 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3427
 kthread+0x711/0x8a0 kernel/kthread.c:463
 ret_from_fork+0x4bc/0x870 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 ffff88802301a000
 which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 544 bytes inside of
 freed 1024-byte region [ffff88802301a000, ffff88802301a400)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x23018
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000040 ffff88801a026dc0 dead000000000100 dead000000000122
raw: 0000000000000000 0000000000100010 00000000f5000000 0000000000000000
head: 00fff00000000040 ffff88801a026dc0 dead000000000100 dead000000000122
head: 0000000000000000 0000000000100010 00000000f5000000 0000000000000000
head: 00fff00000000003 ffffea00008c0601 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 0x52820(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP), pid 1156, tgid 1156 (kworker/u8:6), ts 111574274805, free_ts 110856975269
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x240/0x2a0 mm/page_alloc.c:1850
 prep_new_page mm/page_alloc.c:1858 [inline]
 get_page_from_freelist+0x2365/0x2440 mm/page_alloc.c:3884
 __alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5183
 alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2416
 alloc_slab_page mm/slub.c:3055 [inline]
 allocate_slab+0x96/0x350 mm/slub.c:3228
 new_slab mm/slub.c:3282 [inline]
 ___slab_alloc+0xe94/0x18a0 mm/slub.c:4651
 __slab_alloc+0x65/0x100 mm/slub.c:4770
 __slab_alloc_node mm/slub.c:4846 [inline]
 slab_alloc_node mm/slub.c:5268 [inline]
 __do_kmalloc_node mm/slub.c:5641 [inline]
 __kmalloc_noprof+0x471/0x7f0 mm/slub.c:5654
 kmalloc_noprof include/linux/slab.h:961 [inline]
 kzalloc_noprof include/linux/slab.h:1094 [inline]
 ieee802_11_parse_elems_full+0x152/0x2ab0 net/mac80211/parse.c:1011
 ieee802_11_parse_elems_crc net/mac80211/ieee80211_i.h:2470 [inline]
 ieee802_11_parse_elems net/mac80211/ieee80211_i.h:2477 [inline]
 ieee80211_rx_mgmt_probe_beacon net/mac80211/ibss.c:1569 [inline]
 ieee80211_ibss_rx_queued_mgmt+0x47a/0x2af0 net/mac80211/ibss.c:1600
 ieee80211_iface_process_skb net/mac80211/iface.c:1694 [inline]
 ieee80211_iface_work+0x85f/0x12d0 net/mac80211/iface.c:1748
 cfg80211_wiphy_work+0x2bb/0x470 net/wireless/core.c:435
 process_one_work kernel/workqueue.c:3263 [inline]
 process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3346
 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3427
 kthread+0x711/0x8a0 kernel/kthread.c:463
 ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158
page last free pid 5936 tgid 5936 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1394 [inline]
 __free_frozen_pages+0xbc4/0xd30 mm/page_alloc.c:2906
 discard_slab mm/slub.c:3326 [inline]
 __put_partials+0x146/0x170 mm/slub.c:3872
 put_cpu_partial+0x1f2/0x2e0 mm/slub.c:3947
 __slab_free+0x2b9/0x390 mm/slub.c:5921
 qlink_free mm/kasan/quarantine.c:163 [inline]
 qlist_free_all+0x97/0x140 mm/kasan/quarantine.c:179
 kasan_quarantine_reduce+0x148/0x160 mm/kasan/quarantine.c:286
 __kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:352
 kasan_slab_alloc include/linux/kasan.h:252 [inline]
 slab_post_alloc_hook mm/slub.c:4970 [inline]
 slab_alloc_node mm/slub.c:5280 [inline]
 kmem_cache_alloc_noprof+0x367/0x6e0 mm/slub.c:5287
 getname_flags+0xb8/0x540 fs/namei.c:146
 do_readlinkat+0xbc/0x500 fs/stat.c:575
 __do_sys_readlink fs/stat.c:613 [inline]
 __se_sys_readlink fs/stat.c:610 [inline]
 __x64_sys_readlink+0x7f/0x90 fs/stat.c:610
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff88802301a100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88802301a180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88802301a200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                               ^
 ffff88802301a280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88802301a300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
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
* Struck through repros no longer work on HEAD.