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KASAN: use-after-free Read in seq_printf (2)

Status: premoderation: reported on 2026/01/14 15:56
Reported-by: syzbot+f38eff85cf3bdf63731c@syzkaller.appspotmail.com
First crash: 8d13h, last: 8d13h
▶ ▼ Similar bugs (7)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
android-5-10 KASAN: use-after-free Read in seq_printf 19 15 120d 228d 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 256d 361d 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 125d 129d 0/2 auto-obsoleted due to no activity on 2025/12/19 00:57
android-5-15 KASAN: use-after-free Read in seq_printf 19 1 126d 126d 0/2 auto-obsoleted due to no activity on 2025/12/17 23:30
upstream KMSAN: uninit-value in seq_printf (2) fs 7 C 99 1317d 1584d 0/29 auto-closed as invalid on 2022/09/30 02:43
upstream KMSAN: kernel-infoleak in __skb_datagram_iter net 9 68 849d 954d 23/29 fixed on 2023/09/28 17:51
upstream KASAN: slab-use-after-free Read in seq_printf fs 19 5 14d 107d 0/29 moderation: reported on 2025/10/07 11:49

Sample crash report:
==================================================================
BUG: KASAN: use-after-free in string_nocheck lib/vsprintf.c:641 [inline]
BUG: KASAN: use-after-free in string+0x21f/0x2b0 lib/vsprintf.c:723
Read of size 1 at addr ffff88811b6ac578 by task syz.5.1219/5533

CPU: 0 PID: 5533 Comm: syz.5.1219 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
 __dump_stack+0x21/0x24 lib/dump_stack.c:77
 dump_stack_lvl+0x169/0x1d8 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+0xe2/0x130 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+0x21f/0x2b0 lib/vsprintf.c:723
 vsnprintf+0xed9/0x1960 lib/vsprintf.c:2689
 seq_vprintf fs/seq_file.c:398 [inline]
 seq_printf+0x175/0x260 fs/seq_file.c:413
 input_devices_seq_show+0x14b/0x650 drivers/input/input.c:1184
 seq_read_iter+0x93f/0xd30 fs/seq_file.c:272
 seq_read+0x3cc/0x4d0 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+0x1fe/0xa10 fs/read_write.c:494
 ksys_read+0x140/0x240 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: 0033:0x7fd060398749
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:00007fd05ee00038 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 00007fd0605eefa0 RCX: 00007fd060398749
RDX: 0000000000002020 RSI: 0000200000001040 RDI: 0000000000000004
RBP: 00007fd06041cf91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fd0605ef038 R14: 00007fd0605eefa0 R15: 00007ffd65cdd638

Allocated by task 15:
 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+0xda/0x110 mm/kasan/common.c:518
 kasan_kmalloc include/linux/kasan.h:254 [inline]
 kmem_cache_alloc_trace+0x184/0x2e0 mm/slub.c:2979
 kmalloc include/linux/slab.h:555 [inline]
 kzalloc include/linux/slab.h:667 [inline]
 xpad_probe+0x3f9/0x1a20 drivers/input/joystick/xpad.c:1782
 usb_probe_interface+0x5ff/0xae0 drivers/usb/core/driver.c:397
 really_probe+0x3d8/0xa90 drivers/base/dd.c:562
 driver_probe_device+0xe7/0x190 drivers/base/dd.c:752
 __device_attach_driver+0x282/0x3f0 drivers/base/dd.c:863
 bus_for_each_drv+0x175/0x200 drivers/base/bus.c:433
 __device_attach+0x29a/0x400 drivers/base/dd.c:932
 device_initial_probe+0x1a/0x20 drivers/base/dd.c:981
 bus_probe_device+0xc0/0x1e0 drivers/base/bus.c:493
 device_add+0x8b4/0xbf0 drivers/base/core.c:3273
 usb_set_configuration+0x1a47/0x1f80 drivers/usb/core/message.c:2160
 usb_generic_driver_probe+0x91/0x150 drivers/usb/core/generic.c:238
 usb_probe_device+0x148/0x260 drivers/usb/core/driver.c:294
 really_probe+0x3d8/0xa90 drivers/base/dd.c:562
 driver_probe_device+0xe7/0x190 drivers/base/dd.c:752
 __device_attach_driver+0x282/0x3f0 drivers/base/dd.c:863
 bus_for_each_drv+0x175/0x200 drivers/base/bus.c:433
 __device_attach+0x29a/0x400 drivers/base/dd.c:932
 device_initial_probe+0x1a/0x20 drivers/base/dd.c:981
 bus_probe_device+0xc0/0x1e0 drivers/base/bus.c:493
 device_add+0x8b4/0xbf0 drivers/base/core.c:3273
 usb_new_device+0xcd1/0x1450 drivers/usb/core/hub.c:2654
 hub_port_connect drivers/usb/core/hub.c:5499 [inline]
 hub_port_connect_change drivers/usb/core/hub.c:5639 [inline]
 port_event drivers/usb/core/hub.c:5805 [inline]
 hub_event+0x283f/0x42c0 drivers/usb/core/hub.c:5887
 process_one_work+0x6e1/0xba0 kernel/workqueue.c:2301
 worker_thread+0xa6a/0x13b0 kernel/workqueue.c:2447
 kthread+0x346/0x3d0 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:298

Freed by task 1626:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track+0x4a/0x70 mm/kasan/common.c:45
 kasan_set_free_info+0x23/0x40 mm/kasan/generic.c:370
 ____kasan_slab_free+0x125/0x160 mm/kasan/common.c:362
 __kasan_slab_free+0x11/0x20 mm/kasan/common.c:370
 kasan_slab_free include/linux/kasan.h:220 [inline]
 slab_free_hook mm/slub.c:1600 [inline]
 slab_free_freelist_hook+0xc5/0x190 mm/slub.c:1626
 slab_free mm/slub.c:3208 [inline]
 kfree+0xc0/0x270 mm/slub.c:4196
 skb_free_head net/core/skbuff.c:606 [inline]
 skb_release_data+0x532/0x670 net/core/skbuff.c:626
 skb_release_all net/core/skbuff.c:680 [inline]
 __kfree_skb net/core/skbuff.c:694 [inline]
 consume_skb+0xab/0x1f0 net/core/skbuff.c:851
 netlink_broadcast_filtered+0x117d/0x1270 net/netlink/af_netlink.c:1530
 netlink_broadcast net/netlink/af_netlink.c:1552 [inline]
 nlmsg_multicast include/net/netlink.h:1033 [inline]
 nlmsg_notify+0xed/0x1b0 net/netlink/af_netlink.c:2546
 rtnl_notify+0x9a/0xc0 net/core/rtnetlink.c:737
 inet6_ifa_notify net/ipv6/addrconf.c:5537 [inline]
 __ipv6_ifa_notify+0x233/0xdb0 net/ipv6/addrconf.c:6149
 addrconf_ifdown+0xd5c/0x1800 net/ipv6/addrconf.c:3912
 addrconf_notify+0x3bd/0xe90 net/ipv6/addrconf.c:-1
 notifier_call_chain kernel/notifier.c:83 [inline]
 raw_notifier_call_chain+0x90/0x100 kernel/notifier.c:410
 call_netdevice_notifiers_info net/core/dev.c:2054 [inline]
 call_netdevice_notifiers_extack net/core/dev.c:2066 [inline]
 call_netdevice_notifiers net/core/dev.c:2080 [inline]
 dev_close_many+0x330/0x4d0 net/core/dev.c:1655
 unregister_netdevice_many+0x44c/0x1980 net/core/dev.c:10744
 ip_tunnel_delete_nets+0x343/0x390 net/ipv4/ip_tunnel.c:1122
 ipgre_tap_exit_batch_net+0x22/0x30 net/ipv4/ip_gre.c:1706
 ops_exit_list net/core/net_namespace.c:190 [inline]
 cleanup_net+0x5fb/0xb70 net/core/net_namespace.c:609
 process_one_work+0x6e1/0xba0 kernel/workqueue.c:2301
 worker_thread+0xa6a/0x13b0 kernel/workqueue.c:2447
 kthread+0x346/0x3d0 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
 insert_work+0x52/0x310 kernel/workqueue.c:1352
 __queue_work+0x923/0xca0 kernel/workqueue.c:1518
 queue_work_on+0xd5/0x130 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:851 [inline]
 xpad_irq_in+0xd07/0x1a80 drivers/input/joystick/xpad.c:989
 __usb_hcd_giveback_urb+0x333/0x4f0 drivers/usb/core/hcd.c:1674
 usb_hcd_giveback_urb+0x119/0x410 drivers/usb/core/hcd.c:1748
 dummy_timer+0x804/0x2c30 drivers/usb/gadget/udc/dummy_hcd.c:1975
 call_timer_fn+0x38/0x290 kernel/time/timer.c:1450
 expire_timers kernel/time/timer.c:1495 [inline]
 __run_timers+0x639/0x9a0 kernel/time/timer.c:1789
 run_timer_softirq+0x6a/0xf0 kernel/time/timer.c:1802
 __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+0x52/0x310 kernel/workqueue.c:1352
 __queue_work+0x923/0xca0 kernel/workqueue.c:1518
 queue_work_on+0xd5/0x130 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:851 [inline]
 xpad_irq_in+0xd07/0x1a80 drivers/input/joystick/xpad.c:989
 __usb_hcd_giveback_urb+0x333/0x4f0 drivers/usb/core/hcd.c:1674
 usb_hcd_giveback_urb+0x119/0x410 drivers/usb/core/hcd.c:1748
 dummy_timer+0x804/0x2c30 drivers/usb/gadget/udc/dummy_hcd.c:1975
 call_timer_fn+0x38/0x290 kernel/time/timer.c:1450
 expire_timers kernel/time/timer.c:1495 [inline]
 __run_timers+0x639/0x9a0 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 ffff88811b6ac400
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 376 bytes inside of
 512-byte region [ffff88811b6ac400, ffff88811b6ac600)
The buggy address belongs to the page:
page:ffffea00046dab00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x11b6ac
head:ffffea00046dab00 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head)
raw: 4000000000010200 ffffea0004264c00 0000000400000004 ffff888100043080
raw: 0000000000000000 0000000000100010 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 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 134, ts 5012176650, free_ts 0
 set_page_owner include/linux/page_owner.h:35 [inline]
 post_alloc_hook mm/page_alloc.c:2456 [inline]
 prep_new_page+0x179/0x180 mm/page_alloc.c:2462
 get_page_from_freelist+0x2235/0x23d0 mm/page_alloc.c:4254
 __alloc_pages_nodemask+0x268/0x5f0 mm/page_alloc.c:5370
 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+0x2a6/0x450 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+0x1ef/0x320 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]
 alloc_skb_with_frags+0xa2/0x560 net/core/skbuff.c:5993
 sock_alloc_send_pskb+0x853/0x980 net/core/sock.c:2393
 unix_dgram_sendmsg+0x5f4/0x17d0 net/unix/af_unix.c:1725
 sock_sendmsg_nosec net/socket.c:652 [inline]
 __sock_sendmsg net/socket.c:664 [inline]
 __sys_sendto+0x41d/0x580 net/socket.c:2006
 __do_sys_sendto net/socket.c:2018 [inline]
 __se_sys_sendto net/socket.c:2014 [inline]
 __x64_sys_sendto+0xe5/0x100 net/socket.c:2014
 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x61/0xcb
page_owner free stack trace missing

Memory state around the buggy address:
 ffff88811b6ac400: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88811b6ac480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88811b6ac500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                                ^
 ffff88811b6ac580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88811b6ac600: 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
2026/01/14 15:55 android13-5.10-lts e253c52bbdfc d6526ea3 .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.