KASAN: use-after-free Read in seq_printf (3)

Status: premoderation: reported on 2026/08/30 00:45
Reported-by: syzbot+f36aa1df8927979e175e@syzkaller.appspotmail.com
First crash: 2d22h, last: 2d22h
▶ ▼ Similar bugs (11)
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 2 6d20h 6d20h 0/2 premoderation: reported on 2026/08/26 02:30
android-5-10 KASAN: use-after-free Read in seq_printf 19 15 342d 450d 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 478d 583d 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 346d 351d 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 230d 230d 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 347d 347d 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 1539d 1805d 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 150d 150d 0/2 auto-obsoleted due to no activity on 2026/07/03 17:29
upstream KMSAN: kernel-infoleak in __skb_datagram_iter net 9 68 1071d 1176d 23/29 fixed on 2023/09/28 17:51
upstream KASAN: slab-use-after-free Read in seq_printf prio:high fs 19 28 7d17h 329d 0/29 moderation: reported on 2025/10/07 11:49
linux-6.6 KASAN: slab-use-after-free Read in seq_printf 19 1 7d09h 7d09h 0/2 upstream: reported on 2026/08/25 13:48

Sample crash report:
==================================================================
BUG: KASAN: use-after-free in string_nocheck lib/vsprintf.c:641 [inline]
BUG: KASAN: use-after-free in string+0x20f/0x2a0 lib/vsprintf.c:723
Read of size 1 at addr ffff8881285c6178 by task syz.0.2377/9656

CPU: 0 PID: 9656 Comm: syz.0.2377 Tainted: G        W         syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 __dump_stack+0x21/0x24 lib/dump_stack.c:77
 dump_stack_lvl+0x1a7/0x208 lib/dump_stack.c:118
 print_address_description+0x7f/0x2c0 mm/kasan/report.c:248
 __kasan_report mm/kasan/report.c:435 [inline]
 kasan_report+0x100/0x140 mm/kasan/report.c:452
 __asan_report_load1_noabort+0x14/0x20 mm/kasan/report_generic.c:306
 string_nocheck lib/vsprintf.c:641 [inline]
 string+0x20f/0x2a0 lib/vsprintf.c:723
 vsnprintf+0xec5/0x1990 lib/vsprintf.c:2689
 seq_vprintf fs/seq_file.c:398 [inline]
 seq_printf+0x185/0x280 fs/seq_file.c:413
 input_devices_seq_show+0x14b/0x650 drivers/input/input.c:1184
 seq_read_iter+0x908/0xce0 fs/seq_file.c:272
 seq_read+0x3d9/0x4f0 fs/seq_file.c:162
 pde_read fs/proc/inode.c:321 [inline]
 proc_reg_read+0x1c4/0x2b0 fs/proc/inode.c:333
 vfs_read+0x209/0xa50 fs/read_write.c:494
 ksys_read+0x14a/0x260 fs/read_write.c:634
 __do_sys_read fs/read_write.c:644 [inline]
 __se_sys_read fs/read_write.c:642 [inline]
 __x64_sys_read+0x7b/0x90 fs/read_write.c:642
 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x61/0xcb
RIP: 0033:0x7f1941e12159
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:00007f194086b028 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 00007f1942099fa0 RCX: 00007f1941e12159
RDX: 0000000000002020 RSI: 0000200000006180 RDI: 0000000000000005
RBP: 00007f1941ea9024 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f194209a038 R14: 00007f1942099fa0 R15: 00007fff230f5368

Allocated by task 7658:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track mm/kasan/common.c:45 [inline]
 set_alloc_info mm/kasan/common.c:430 [inline]
 ____kasan_kmalloc mm/kasan/common.c:509 [inline]
 __kasan_kmalloc+0xd4/0x100 mm/kasan/common.c:518
 kasan_kmalloc include/linux/kasan.h:254 [inline]
 kmem_cache_alloc_trace+0x179/0x2e0 mm/slub.c:2979
 kmalloc include/linux/slab.h:555 [inline]
 kzalloc include/linux/slab.h:667 [inline]
 find_css_set+0x969/0x1620 kernel/cgroup/cgroup.c:1238
 cgroup_migrate_prepare_dst+0xc4/0xa00 kernel/cgroup/cgroup.c:2787
 cgroup_attach_task+0x298/0x520 kernel/cgroup/cgroup.c:2893
 cgroup_attach_task_all+0xb4/0x140 kernel/cgroup/cgroup-v1.c:73
 kvm_vm_worker_thread+0xcb/0x280 virt/kvm/kvm_main.c:5106
 kthread+0x324/0x3b0 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:298

Last potentially related work creation:
 kasan_save_stack+0x3a/0x60 mm/kasan/common.c:38
 __kasan_record_aux_stack+0xd2/0x100 mm/kasan/generic.c:348
 kasan_record_aux_stack_noalloc+0xb/0x10 mm/kasan/generic.c:358
 kvfree_call_rcu+0x117/0x670 kernel/rcu/tree.c:3539
 put_css_set_locked+0xa0a/0xa40 kernel/cgroup/cgroup.c:1003
 put_css_set kernel/cgroup/cgroup-internal.h:210 [inline]
 cgroup_free+0x68/0x80 kernel/cgroup/cgroup.c:6468
 __put_task_struct+0xb4/0x420 kernel/fork.c:777
 put_task_struct include/linux/sched/task.h:143 [inline]
 delayed_put_task_struct+0x6f/0x1a0 kernel/exit.c:227
 rcu_do_batch+0x488/0xaf0 kernel/rcu/tree.c:2494
 rcu_core+0x50a/0xca0 kernel/rcu/tree.c:2735
 rcu_core_si+0x9/0x10 kernel/rcu/tree.c:2748
 __do_softirq+0x255/0x563 kernel/softirq.c:309

Second to last potentially related work creation:
 kasan_save_stack+0x3a/0x60 mm/kasan/common.c:38
 __kasan_record_aux_stack+0xd2/0x100 mm/kasan/generic.c:348
 kasan_record_aux_stack_noalloc+0xb/0x10 mm/kasan/generic.c:358
 insert_work+0x51/0x320 kernel/workqueue.c:1352
 __queue_work+0x91f/0xca0 kernel/workqueue.c:1518
 queue_work_on+0xe6/0x140 kernel/workqueue.c:1545
 queue_work include/linux/workqueue.h:515 [inline]
 schedule_work include/linux/workqueue.h:576 [inline]
 xpad360w_process_packet drivers/input/joystick/xpad.c:853 [inline]
 xpad_irq_in+0xd26/0x1a60 drivers/input/joystick/xpad.c:991
 __usb_hcd_giveback_urb+0x32f/0x4f0 drivers/usb/core/hcd.c:1672
 usb_hcd_giveback_urb+0x11d/0x3f0 drivers/usb/core/hcd.c:1746
 dummy_timer+0xa3a/0x32d0 drivers/usb/gadget/udc/dummy_hcd.c:2000
 call_timer_fn+0x38/0x290 kernel/time/timer.c:1450
 expire_timers kernel/time/timer.c:1495 [inline]
 __run_timers+0x637/0x9a0 kernel/time/timer.c:1789
 run_timer_softirq+0x6a/0xf0 kernel/time/timer.c:1802
 __do_softirq+0x255/0x563 kernel/softirq.c:309

The buggy address belongs to the object at ffff8881285c6000
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 376 bytes inside of
 512-byte region [ffff8881285c6000, ffff8881285c6200)
The buggy address belongs to the page:
page:ffffea0004a17100 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff8881285c6400 pfn:0x1285c4
head:ffffea0004a17100 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head)
raw: 4000000000010200 ffffea00041ff308 ffffea0004511008 ffff888100043080
raw: ffff8881285c6400 000000000010000c 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 2, migratetype Unmovable, gfp_mask 0x1d2a20(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 302, ts 25767414411, free_ts 25340730738
 set_page_owner include/linux/page_owner.h:35 [inline]
 post_alloc_hook mm/page_alloc.c:2456 [inline]
 prep_new_page+0x176/0x190 mm/page_alloc.c:2462
 get_page_from_freelist+0x225f/0x23f0 mm/page_alloc.c:4254
 __alloc_pages_nodemask+0x29a/0x640 mm/page_alloc.c:5384
 alloc_slab_page mm/slub.c:-1 [inline]
 allocate_slab mm/slub.c:1813 [inline]
 new_slab+0x84/0x3f0 mm/slub.c:1874
 new_slab_objects mm/slub.c:2632 [inline]
 ___slab_alloc+0x2f8/0x4c0 mm/slub.c:2796
 __slab_alloc+0x63/0xa0 mm/slub.c:2836
 slab_alloc_node mm/slub.c:2918 [inline]
 slab_alloc mm/slub.c:2960 [inline]
 __kmalloc_track_caller+0x1e4/0x310 mm/slub.c:4541
 __kmalloc_reserve net/core/skbuff.c:144 [inline]
 __alloc_skb+0xdc/0x520 net/core/skbuff.c:212
 alloc_skb include/linux/skbuff.h:1126 [inline]
 ndisc_alloc_skb net/ipv6/ndisc.c:422 [inline]
 ndisc_send_rs+0x310/0x960 net/ipv6/ndisc.c:691
 addrconf_dad_completed+0x945/0xe30 net/ipv6/addrconf.c:4293
 addrconf_dad_work+0xc5f/0x1480 net/ipv6/addrconf.c:-1
 process_one_work+0x6fd/0xbc0 kernel/workqueue.c:2301
 worker_thread+0xa8e/0x13c0 kernel/workqueue.c:2447
 kthread+0x324/0x3b0 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:298
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:28 [inline]
 free_pages_prepare mm/page_alloc.c:1349 [inline]
 __free_pages_ok+0x80b/0x830 mm/page_alloc.c:1629
 free_the_page mm/page_alloc.c:5445 [inline]
 __free_pages+0xd8/0x390 mm/page_alloc.c:5454
 kfree+0x1e4/0x270 mm/slub.c:4193
 kvfree+0x35/0x40 mm/util.c:647
 btf_add_type kernel/bpf/btf.c:1421 [inline]
 btf_check_all_metas+0x42c/0x820 kernel/bpf/btf.c:3814
 btf_parse_vmlinux+0x43e/0xab0 kernel/bpf/btf.c:4388
 bpf_get_btf_vmlinux kernel/bpf/verifier.c:12588 [inline]
 bpf_check+0x5ed/0xdce0 kernel/bpf/verifier.c:12627
 bpf_prog_load+0x1004/0x14e0 kernel/bpf/syscall.c:2234
 __do_sys_bpf kernel/bpf/syscall.c:4435 [inline]
 __se_sys_bpf+0x49a/0x740 kernel/bpf/syscall.c:4391
 __x64_sys_bpf+0x7b/0x90 kernel/bpf/syscall.c:4391
 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x61/0xcb

Memory state around the buggy address:
 ffff8881285c6000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8881285c6080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8881285c6100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                                ^
 ffff8881285c6180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff8881285c6200: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/30 00:44 android13-5.10-lts 174d3ccb72b8 2f52988a .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in seq_printf
* Struck through repros no longer work on HEAD.