KASAN: slab-out-of-bounds Read in do_update_region

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: dce0f886 Linux 4.19.132
git tree: linux-4.19.y
console output: https://syzkaller.appspot.com/x/log.txt?x=146f9333100000
kernel config: https://syzkaller.appspot.com/x/.config?x=630ac1b7a61d1805
dashboard link: https://syzkaller.appspot.com/bug?extid=140b8da1d97d42994963
compiler: gcc (GCC) 10.1.0-syz 20200507

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

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+140b8d...@syzkaller.appspotmail.com

IPv6: ADDRCONF(NETDEV_CHANGE): vxcan1: link becomes ready
==================================================================
BUG: KASAN: slab-out-of-bounds in do_update_region+0x5aa/0x630 drivers/tty/vt/vt.c:671
Read of size 2 at addr ffff88809a52eaf8 by task syz-executor.4/28507

CPU: 1 PID: 28507 Comm: syz-executor.4 Not tainted 4.19.132-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x1fc/0x2fe lib/dump_stack.c:118
print_address_description.cold+0x54/0x219 mm/kasan/report.c:256
kasan_report_error.cold+0x8a/0x1c7 mm/kasan/report.c:354
kasan_report mm/kasan/report.c:412 [inline]
__asan_report_load2_noabort+0x88/0x90 mm/kasan/report.c:431
do_update_region+0x5aa/0x630 drivers/tty/vt/vt.c:671
update_region+0x144/0x190 drivers/tty/vt/vt.c:701
vcs_write+0x403/0xc30 drivers/tty/vt/vc_screen.c:604
__vfs_write+0xf7/0x770 fs/read_write.c:485
vfs_write+0x1f3/0x540 fs/read_write.c:549
ksys_write+0x12b/0x2a0 fs/read_write.c:599
do_syscall_64+0xf9/0x620 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45cba9
Code: 8d b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 0f 83 5b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fc98a2eac78 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 000000000050d800 RCX: 000000000045cba9
RDX: 0000000000000028 RSI: 0000000020000080 RDI: 0000000000000003
RBP: 000000000078bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 0000000000000cec R14: 00000000004cf3b3 R15: 00007fc98a2eb6d4

Allocated by task 31259:
__do_kmalloc mm/slab.c:3727 [inline]
__kmalloc+0x15a/0x3c0 mm/slab.c:3736
kmalloc include/linux/slab.h:520 [inline]
kzalloc include/linux/slab.h:709 [inline]
vc_do_resize+0x2fc/0x1440 drivers/tty/vt/vt.c:1220
fbcon_modechanged+0x4df/0x9f0 drivers/video/fbdev/core/fbcon.c:2961
fbcon_event_notify+0x197/0x1d80 drivers/video/fbdev/core/fbcon.c:3347
notifier_call_chain+0xc0/0x230 kernel/notifier.c:93
__blocking_notifier_call_chain kernel/notifier.c:317 [inline]
__blocking_notifier_call_chain kernel/notifier.c:304 [inline]
blocking_notifier_call_chain kernel/notifier.c:328 [inline]
blocking_notifier_call_chain+0x85/0xa0 kernel/notifier.c:325
fb_set_var+0xc51/0xe20 drivers/video/fbdev/core/fbmem.c:1042
do_fb_ioctl+0x3cf/0xb50 drivers/video/fbdev/core/fbmem.c:1115
fb_ioctl+0xdd/0x130 drivers/video/fbdev/core/fbmem.c:1230
vfs_ioctl fs/ioctl.c:46 [inline]
file_ioctl fs/ioctl.c:501 [inline]
do_vfs_ioctl+0xcdb/0x12e0 fs/ioctl.c:688
ksys_ioctl+0x9b/0xc0 fs/ioctl.c:705
__do_sys_ioctl fs/ioctl.c:712 [inline]
__se_sys_ioctl fs/ioctl.c:710 [inline]
__x64_sys_ioctl+0x6f/0xb0 fs/ioctl.c:710
do_syscall_64+0xf9/0x620 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 9:
__cache_free mm/slab.c:3503 [inline]
kfree+0xcc/0x210 mm/slab.c:3822
__rcu_reclaim kernel/rcu/rcu.h:231 [inline]
rcu_do_batch kernel/rcu/tree.c:2584 [inline]
invoke_rcu_callbacks kernel/rcu/tree.c:2897 [inline]
__rcu_process_callbacks kernel/rcu/tree.c:2864 [inline]
rcu_process_callbacks+0xa0d/0x18b0 kernel/rcu/tree.c:2881
__do_softirq+0x26c/0x9a0 kernel/softirq.c:292

The buggy address belongs to the object at ffff88809a52ea80
which belongs to the cache kmalloc-128 of size 128
The buggy address is located 120 bytes inside of
128-byte region [ffff88809a52ea80, ffff88809a52eb00)
The buggy address belongs to the page:
page:ffffea0002694b80 count:1 mapcount:0 mapping:ffff88812c39c640 index:0x0
flags: 0xfffe0000000100(slab)
raw: 00fffe0000000100 ffffea00021f6448 ffffea000283af08 ffff88812c39c640
raw: 0000000000000000 ffff88809a52e000 0000000100000015 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff88809a52e980: fc fc fc fc fc fc fc fc 00 00 00 00 00 00 00 00
ffff88809a52ea00: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
>ffff88809a52ea80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 fc
^
ffff88809a52eb00: fc fc fc fc fc fc fc fc 00 00 00 00 00 00 00 00
ffff88809a52eb80: 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc
==================================================================


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.