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: 4d00h, last: 4d00h
▶ ▼ Similar bugs (14)
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 10 5h10m 32d 0/2 premoderation: reported on 2026/08/26 02:30
android-5-10 KASAN: use-after-free Read in seq_printf (3) 19 8 12h12m 28d 0/2 premoderation: reported on 2026/08/30 00:45
android-5-10 KASAN: use-after-free Read in seq_printf 19 15 368d 475d 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 503d 609d 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 372d 377d 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 255d 255d 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 19 syz, C 6 5h40m 2d17h 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 373d 373d 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 1565d 1831d 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 175d 175d 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 19 3 2d08h 4d09h 0/1 premoderation: reported on 2026/09/23 06:02
upstream KMSAN: kernel-infoleak in __skb_datagram_iter net 9 68 1097d 1202d 23/29 fixed on 2023/09/28 17:51
upstream KASAN: slab-use-after-free Read in seq_printf prio:high fs 19 70 1d18h 8d12h 0/29 upstream: reported on 2026/09/19 02:15
linux-6.6 KASAN: slab-use-after-free Read in seq_printf 19 1 33d 33d 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 ffff8881478a08e8 by task syz.9.1543/10910

CPU: 1 PID: 10910 Comm: syz.9.1543 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
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: 0033:0x7fe8c8041159
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:00007fe8c6299028 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 00007fe8c82c8fa0 RCX: 00007fe8c8041159
RDX: 0000000000002020 RSI: 0000200000000340 RDI: 0000000000000003
RBP: 00007fe8c80d806b R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fe8c82c9038 R14: 00007fe8c82c8fa0 R15: 00007ffd99933158
 </TASK>

Allocated by task 1108:
 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 include/linux/slab.h:607 [inline]
 usb_control_msg+0x70/0x3e0 drivers/usb/core/message.c:156
 usb_get_descriptor+0xad/0x3d0 drivers/usb/core/message.c:851
 usb_get_configuration+0x298/0x51f0 drivers/usb/core/config.c:923
 usb_enumerate_device drivers/usb/core/hub.c:2469 [inline]
 usb_new_device+0x121/0x15d0 drivers/usb/core/hub.c:2607
 hub_port_connect drivers/usb/core/hub.c:5502 [inline]
 hub_port_connect_change drivers/usb/core/hub.c:5642 [inline]
 port_event drivers/usb/core/hub.c:5804 [inline]
 hub_event+0x2b8d/0x5260 drivers/usb/core/hub.c:5886
 process_one_work+0x867/0xff0 kernel/workqueue.c:2310
 worker_thread+0xad7/0x12a0 kernel/workqueue.c:2457
 kthread+0x42e/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287

Freed by task 1108:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track+0x4b/0x70 mm/kasan/common.c:46
 kasan_set_free_info+0x1f/0x40 mm/kasan/generic.c:360
 ____kasan_slab_free+0xd5/0x110 mm/kasan/common.c:366
 kasan_slab_free include/linux/kasan.h:230 [inline]
 slab_free_hook mm/slub.c:1710 [inline]
 slab_free_freelist_hook+0xec/0x170 mm/slub.c:1736
 slab_free mm/slub.c:3504 [inline]
 kfree+0xef/0x2a0 mm/slub.c:4564
 usb_control_msg+0x2be/0x3e0 drivers/usb/core/message.c:172
 usb_get_descriptor+0xad/0x3d0 drivers/usb/core/message.c:851
 usb_get_configuration+0x298/0x51f0 drivers/usb/core/config.c:923
 usb_enumerate_device drivers/usb/core/hub.c:2469 [inline]
 usb_new_device+0x121/0x15d0 drivers/usb/core/hub.c:2607
 hub_port_connect drivers/usb/core/hub.c:5502 [inline]
 hub_port_connect_change drivers/usb/core/hub.c:5642 [inline]
 port_event drivers/usb/core/hub.c:5804 [inline]
 hub_event+0x2b8d/0x5260 drivers/usb/core/hub.c:5886
 process_one_work+0x867/0xff0 kernel/workqueue.c:2310
 worker_thread+0xad7/0x12a0 kernel/workqueue.c:2457
 kthread+0x42e/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287

The buggy address belongs to the object at ffff8881478a08e8
 which belongs to the cache kmalloc-8 of size 8
The buggy address is located 0 bytes inside of
 8-byte region [ffff8881478a08e8, ffff8881478a08f0)
The buggy address belongs to the page:
page:ffffea00051e2800 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1478a0
flags: 0x57ff00000000200(slab|node=1|zone=2|lastcpupid=0x7ff)
raw: 057ff00000000200 ffffea0005127200 0000001500000015 ffff888016c41280
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, ts 6956961614, 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_track_caller+0x11b/0x330 mm/slub.c:4930
 kstrdup mm/util.c:60 [inline]
 kstrdup_const+0x51/0x90 mm/util.c:83
 __kernfs_new_node+0xa8/0x6b0 fs/kernfs/dir.c:589
 kernfs_new_node+0x148/0x250 fs/kernfs/dir.c:669
 kernfs_create_link+0xa3/0x200 fs/kernfs/symlink.c:39
 sysfs_do_create_link_sd+0x83/0x110 fs/sysfs/symlink.c:44
 device_create_sys_dev_entry+0x11b/0x180 drivers/base/core.c:3237
 device_add+0xb24/0x1050 drivers/base/core.c:3379
 tty_register_device_attr+0x434/0x9d0 drivers/tty/tty_io.c:3292
 tty_register_device drivers/tty/tty_io.c:3226 [inline]
 tty_register_driver+0x5d4/0xb80 drivers/tty/tty_io.c:3484
 legacy_pty_init+0x3c1/0x600 drivers/tty/pty.c:581
page_owner free stack trace missing

Memory state around the buggy address:
 ffff8881478a0780: 06 fc fc fc fc 06 fc fc fc fc 06 fc fc fc fc 06
 ffff8881478a0800: fc fc fc fc 06 fc fc fc fc 00 fc fc fc fc 00 fc
>ffff8881478a0880: fc fc fc 04 fc fc fc fc fa fc fc fc fc fa fc fc
                                                          ^
 ffff8881478a0900: fc fc 05 fc fc fc fc 00 fc fc fc fc 00 fc fc fc
 ffff8881478a0980: fc fa fc fc fc fc 05 fc fc fc fc 05 fc fc fc fc
==================================================================

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
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.