[moderation] [serial?] KASAN: slab-use-after-free Read in kbd_event (2)

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Apr 6, 2026, 3:32:35 PM (19 hours ago) Apr 6
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Hello,

syzbot found the following issue on:

HEAD commit: 5619b098e2fb Merge tag 'for-7.0-rc6-tag' of git://git.kern..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=101c41ca580000
kernel config: https://syzkaller.appspot.com/x/.config?x=45cb3c58fd963c27
dashboard link: https://syzkaller.appspot.com/bug?extid=d584739ca620aa326525
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
CC: [gre...@linuxfoundation.org jiri...@kernel.org linux-...@vger.kernel.org linux-...@vger.kernel.org]

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/63964c15e763/disk-5619b098.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/86e80eed2888/vmlinux-5619b098.xz
kernel image: https://storage.googleapis.com/syzbot-assets/17dba94dbc66/bzImage-5619b098.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d58473...@syzkaller.appspotmail.com

==================================================================
BUG: KASA[ 730.192938][ T7920] BUG: KASAN: slab-use-after-free in kbd_keycode drivers/tty/vt/keyboard.c:1435 [inline]
BUG: KASA[ 730.192938][ T7920] BUG: KASAN: slab-use-after-free in kbd_event+0x3330/0x40d0 drivers/tty/vt/keyboard.c:1515
Read of size 4 at addr ffff88806944e35c by task syz.2.13424/7920

CPU: 1 UID: 0 PID: 7920 Comm: syz.2.13424 Tainted: G L syzkaller #0 PREEMPT_{RT,(full)}
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
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
kbd_keycode drivers/tty/vt/keyboard.c:1435 [inline]
kbd_event+0x3330/0x40d0 drivers/tty/vt/keyboard.c:1515
input_handle_events_default+0xd4/0x1a0 drivers/input/input.c:2541
input_pass_values+0x288/0x890 drivers/input/input.c:128
input_event_dispose+0x330/0x6b0 drivers/input/input.c:342
input_inject_event+0x1d8/0x330 drivers/input/input.c:424
evdev_write+0x328/0x4c0 drivers/input/evdev.c:528
vfs_write+0x2a3/0xba0 fs/read_write.c:686
ksys_write+0x156/0x270 fs/read_write.c:740
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: 0033:0x7f5547bac819
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:00007f5545dfe028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f5547e25fa0 RCX: 00007f5547bac819
RDX: 0000000000002250 RSI: 0000200000000040 RDI: 0000000000000003
RBP: 00007f5547c42c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f5547e26038 R14: 00007f5547e25fa0 R15: 00007ffe04f8cf48
</TASK>

Allocated by task 7915:
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]
__kmalloc_cache_noprof+0x3a6/0x690 mm/slub.c:5380
kmalloc_noprof include/linux/slab.h:950 [inline]
kzalloc_noprof include/linux/slab.h:1188 [inline]
alloc_tty_struct+0xa6/0x7b0 drivers/tty/tty_io.c:3102
tty_init_dev+0x59/0x4d0 drivers/tty/tty_io.c:1400
tty_open_by_driver drivers/tty/tty_io.c:2073 [inline]
tty_open+0x86e/0xd80 drivers/tty/tty_io.c:2120
chrdev_open+0x4d0/0x5f0 fs/char_dev.c:411
do_dentry_open+0x83d/0x13e0 fs/open.c:949
vfs_open+0x3b/0x350 fs/open.c:1081
do_open fs/namei.c:4677 [inline]
path_openat+0x2e43/0x38a0 fs/namei.c:4836
do_file_open+0x23e/0x4a0 fs/namei.c:4865
do_sys_openat2+0x113/0x200 fs/open.c:1366
do_sys_open fs/open.c:1372 [inline]
__do_sys_openat fs/open.c:1388 [inline]
__se_sys_openat fs/open.c:1383 [inline]
__x64_sys_openat+0x138/0x170 fs/open.c:1383
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

Freed by task 15095:
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+0x1c1/0x6c0 mm/slub.c:6483
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

Last potentially related work creation:
kasan_save_stack+0x3e/0x60 mm/kasan/common.c:57
kasan_record_aux_stack+0xbd/0xd0 mm/kasan/generic.c:556
insert_work+0x3d/0x330 kernel/workqueue.c:2199
__queue_work+0xcc6/0xff0 kernel/workqueue.c:2354
queue_work_on+0x106/0x1d0 kernel/workqueue.c:2405
tty_release_struct+0xb8/0xd0 drivers/tty/tty_io.c:1692
tty_release+0xcb6/0x1710 drivers/tty/tty_io.c:1852
__fput+0x461/0xa90 fs/file_table.c:469
task_work_run+0x1d9/0x270 kernel/task_work.c:233
resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
__exit_to_user_mode_loop kernel/entry/common.c:67 [inline]
exit_to_user_mode_loop+0xed/0x480 kernel/entry/common.c:98
__exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:325 [inline]
do_syscall_64+0x32d/0xf80 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff88806944e000
which belongs to the cache kmalloc-cg-2k of size 2048
The buggy address is located 860 bytes inside of
freed 2048-byte region [ffff88806944e000, ffff88806944e800)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x69448
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
memcg:ffff888069448811
flags: 0x80000000000040(head|node=0|zone=1)
page_type: f5(slab)
raw: 0080000000000040 ffff88813fe363c0 dead000000000100 dead000000000122
raw: 0000000000000000 0000100000080008 00000000f5000000 ffff888069448811
head: 0080000000000040 ffff88813fe363c0 dead000000000100 dead000000000122
head: 0000000000000000 0000100000080008 00000000f5000000 ffff888069448811
head: 0080000000000003 ffffea0001a51201 00000000ffffffff 00000000ffffffff
head: 0000000000000000 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 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 5878, tgid 5878 (syz-executor), ts 463972954830, free_ts 463959021215
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+0x28bb/0x2950 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+0x334/0x3c0 mm/slub.c:7175
refill_sheaf mm/slub.c:2812 [inline]
__pcs_replace_empty_main+0x35c/0x710 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]
__kvmalloc_node_noprof+0x6f4/0x8e0 mm/slub.c:6752
alloc_fdtable+0x101/0x2c0 fs/file.c:219
dup_fd+0x879/0xb70 fs/file.c:420
copy_files+0xc8/0x120 kernel/fork.c:1636
copy_process+0x1767/0x3cd0 kernel/fork.c:2211
kernel_clone+0x249/0x840 kernel/fork.c:2653
__do_sys_clone kernel/fork.c:2794 [inline]
__se_sys_clone kernel/fork.c:2778 [inline]
__x64_sys_clone+0x1b6/0x230 kernel/fork.c:2778
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
page last free pid 1186 tgid 1186 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
__free_pages_prepare mm/page_alloc.c:1433 [inline]
__free_frozen_pages+0xfe3/0x1170 mm/page_alloc.c:2978
__folio_put+0x25d/0x310 mm/swap.c:112
put_netmem include/net/netmem.h:420 [inline]
skb_page_unref include/linux/skbuff_ref.h:43 [inline]
__skb_frag_unref include/linux/skbuff_ref.h:56 [inline]
skb_release_data+0x4cb/0x940 net/core/skbuff.c:1122
skb_release_all net/core/skbuff.c:1203 [inline]
__kfree_skb+0x5d/0x210 net/core/skbuff.c:1217
skb_defer_free_flush+0x191/0x260 net/core/dev.c:6837
net_rx_action+0x4a6/0xe00 net/core/dev.c:7910
handle_softirqs+0x1de/0x6f0 kernel/softirq.c:622
__do_softirq kernel/softirq.c:656 [inline]
__local_bh_enable_ip+0x170/0x2b0 kernel/softirq.c:302
local_bh_enable include/linux/bottom_half.h:33 [inline]
irq_forced_thread_fn+0xe9/0x120 kernel/irq/manage.c:1168
irq_thread+0x4c9/0x740 kernel/irq/manage.c:1271
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

Memory state around the buggy address:
ffff88806944e200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88806944e280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88806944e300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88806944e380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88806944e400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
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