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

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: e4c26faa Merge tag 'usb-5.9-rc5' of git://git.kernel.org/p..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=132e6253900000
kernel config: https://syzkaller.appspot.com/x/.config?x=c61610091f4ca8c4
dashboard link: https://syzkaller.appspot.com/bug?extid=f91d979f99fe699f08e0
compiler: gcc (GCC) 10.1.0-syz 20200507

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

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f91d97...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-out-of-bounds in do_update_region+0x5aa/0x630 drivers/tty/vt/vt.c:663
Read of size 2 at addr ffff888218bbd2c0 by task syz-executor.3/21923

CPU: 1 PID: 21923 Comm: syz-executor.3 Not tainted 5.9.0-rc4-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+0x198/0x1fd lib/dump_stack.c:118
print_address_description.constprop.0.cold+0xae/0x497 mm/kasan/report.c:383
__kasan_report mm/kasan/report.c:513 [inline]
kasan_report.cold+0x1f/0x37 mm/kasan/report.c:530
do_update_region+0x5aa/0x630 drivers/tty/vt/vt.c:663
update_region+0xb5/0x140 drivers/tty/vt/vt.c:693
vcs_write+0x403/0xc30 drivers/tty/vt/vc_screen.c:623
do_loop_readv_writev fs/read_write.c:737 [inline]
do_loop_readv_writev fs/read_write.c:721 [inline]
do_iter_write+0x489/0x670 fs/read_write.c:1020
vfs_writev+0x1aa/0x2e0 fs/read_write.c:1091
do_writev+0x139/0x300 fs/read_write.c:1134
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45d5f9
Code: 5d b4 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 2b b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f831f788c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000014
RAX: ffffffffffffffda RBX: 0000000000039c40 RCX: 000000000045d5f9
RDX: 0000000000000002 RSI: 0000000020000380 RDI: 0000000000000003
RBP: 000000000118cf80 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000118cf4c
R13: 00007ffc44f8988f R14: 00007f831f7899c0 R15: 000000000118cf4c

Allocated by task 1:
kasan_save_stack+0x1b/0x40 mm/kasan/common.c:48
kasan_set_track mm/kasan/common.c:56 [inline]
__kasan_kmalloc.constprop.0+0xbf/0xd0 mm/kasan/common.c:461
__do_kmalloc mm/slab.c:3655 [inline]
__kmalloc+0x1b0/0x310 mm/slab.c:3664
kmalloc include/linux/slab.h:559 [inline]
kzalloc include/linux/slab.h:666 [inline]
vc_do_resize+0x2f6/0x1150 drivers/tty/vt/vt.c:1228
fbcon_init+0x1319/0x1b00 drivers/video/fbdev/core/fbcon.c:1218
visual_init+0x30e/0x5d0 drivers/tty/vt/vt.c:1074
do_bind_con_driver.isra.0+0x549/0x8e0 drivers/tty/vt/vt.c:3658
do_take_over_console+0x423/0x570 drivers/tty/vt/vt.c:4238
do_fbcon_takeover+0x10b/0x210 drivers/video/fbdev/core/fbcon.c:588
fbcon_fb_registered+0x26b/0x340 drivers/video/fbdev/core/fbcon.c:3283
do_register_framebuffer drivers/video/fbdev/core/fbmem.c:1660 [inline]
register_framebuffer+0x587/0x980 drivers/video/fbdev/core/fbmem.c:1828
vga16fb_probe+0x6b4/0x7b5 drivers/video/fbdev/vga16fb.c:1373
platform_drv_probe+0x87/0x140 drivers/base/platform.c:747
really_probe+0x282/0x9f0 drivers/base/dd.c:553
driver_probe_device+0xfe/0x1d0 drivers/base/dd.c:738
__device_attach_driver+0x1c2/0x220 drivers/base/dd.c:844
bus_for_each_drv+0x15f/0x1e0 drivers/base/bus.c:431
__device_attach+0x228/0x470 drivers/base/dd.c:912
bus_probe_device+0x1e4/0x290 drivers/base/bus.c:491
device_add+0xb17/0x1c40 drivers/base/core.c:2926
platform_device_add+0x34f/0x6d0 drivers/base/platform.c:597
vga16fb_init+0x152/0x1c8 drivers/video/fbdev/vga16fb.c:1431
do_one_initcall+0x10a/0x7a4 init/main.c:1204
do_initcall_level init/main.c:1277 [inline]
do_initcalls init/main.c:1293 [inline]
do_basic_setup init/main.c:1313 [inline]
kernel_init_freeable+0x5e9/0x66d init/main.c:1512
kernel_init+0xd/0x1c0 init/main.c:1402
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294

The buggy address belongs to the object at ffff888218bbc000
which belongs to the cache kmalloc-8k of size 8192
The buggy address is located 4800 bytes inside of
8192-byte region [ffff888218bbc000, ffff888218bbe000)
The buggy address belongs to the page:
page:00000000b53090a6 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x218bbc
head:00000000b53090a6 order:2 compound_mapcount:0 compound_pincount:0
flags: 0x57ffe0000010200(slab|head)
raw: 057ffe0000010200 ffffea0008654508 ffffea0008603708 ffff8880aa040a00
raw: 0000000000000000 ffff888218bbc000 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff888218bbd180: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff888218bbd200: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff888218bbd280: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
^
ffff888218bbd300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff888218bbd380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


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[syzbot]

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