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SubjectKASAN: slab-out-of-bounds Read in vc_do_resize
From
Hello,

syzbot found the following crash on:

HEAD commit: 2187f215 Merge tag 'for-5.5-rc2-tag' of git://git.kernel.o..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16b0f2fee00000
kernel config: https://syzkaller.appspot.com/x/.config?x=ab2ae0615387ef78
dashboard link: https://syzkaller.appspot.com/bug?extid=c37a14770d51a085a520
compiler: gcc (GCC) 9.0.0 20181231 (experimental)

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+c37a14770d51a085a520@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-out-of-bounds in memcpy include/linux/string.h:380 [inline]
BUG: KASAN: slab-out-of-bounds in scr_memcpyw include/linux/vt_buffer.h:49
[inline]
BUG: KASAN: slab-out-of-bounds in vc_do_resize+0x959/0x1460
drivers/tty/vt/vt.c:1250
Read of size 2 at addr ffff8880a284cd8c by task syz-executor.0/13609

CPU: 1 PID: 13609 Comm: syz-executor.0 Not tainted 5.5.0-rc2-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+0x197/0x210 lib/dump_stack.c:118
print_address_description.constprop.0.cold+0xd4/0x30b mm/kasan/report.c:374
__kasan_report.cold+0x1b/0x41 mm/kasan/report.c:506
kasan_report+0x12/0x20 mm/kasan/common.c:639
check_memory_region_inline mm/kasan/generic.c:185 [inline]
check_memory_region+0x134/0x1a0 mm/kasan/generic.c:192
memcpy+0x24/0x50 mm/kasan/common.c:125
memcpy include/linux/string.h:380 [inline]
scr_memcpyw include/linux/vt_buffer.h:49 [inline]
vc_do_resize+0x959/0x1460 drivers/tty/vt/vt.c:1250
vc_resize+0x4d/0x60 drivers/tty/vt/vt.c:1304
fbcon_modechanged+0x367/0x790 drivers/video/fbdev/core/fbcon.c:2980
fbcon_update_vcs+0x42/0x50 drivers/video/fbdev/core/fbcon.c:3038
fb_set_var+0xb32/0xdd0 drivers/video/fbdev/core/fbmem.c:1051
do_fb_ioctl+0x390/0x7d0 drivers/video/fbdev/core/fbmem.c:1104
fb_ioctl+0xe6/0x130 drivers/video/fbdev/core/fbmem.c:1180
vfs_ioctl fs/ioctl.c:47 [inline]
file_ioctl fs/ioctl.c:545 [inline]
do_vfs_ioctl+0x977/0x14e0 fs/ioctl.c:732
ksys_ioctl+0xab/0xd0 fs/ioctl.c:749
__do_sys_ioctl fs/ioctl.c:756 [inline]
__se_sys_ioctl fs/ioctl.c:754 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:754
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45a919
Code: ad 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 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fe4a3fd6c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000045a919
RDX: 0000000020000000 RSI: 0000000000004601 RDI: 0000000000000004
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fe4a3fd76d4
R13: 00000000004c310d R14: 00000000004d8478 R15: 00000000ffffffff

Allocated by task 13609:
save_stack+0x23/0x90 mm/kasan/common.c:72
set_track mm/kasan/common.c:80 [inline]
__kasan_kmalloc mm/kasan/common.c:513 [inline]
__kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:486
kasan_kmalloc+0x9/0x10 mm/kasan/common.c:527
__do_kmalloc mm/slab.c:3656 [inline]
__kmalloc+0x163/0x770 mm/slab.c:3665
kmalloc include/linux/slab.h:561 [inline]
kzalloc include/linux/slab.h:670 [inline]
vc_do_resize+0x262/0x1460 drivers/tty/vt/vt.c:1187
vc_resize+0x4d/0x60 drivers/tty/vt/vt.c:1304
fbcon_modechanged+0x367/0x790 drivers/video/fbdev/core/fbcon.c:2980
fbcon_update_vcs+0x42/0x50 drivers/video/fbdev/core/fbcon.c:3038
fb_set_var+0xb32/0xdd0 drivers/video/fbdev/core/fbmem.c:1051
fbcon_resize+0x6b1/0x780 drivers/video/fbdev/core/fbcon.c:2222
resize_screen drivers/tty/vt/vt.c:1126 [inline]
vc_do_resize+0x440/0x1460 drivers/tty/vt/vt.c:1205
vc_resize+0x4d/0x60 drivers/tty/vt/vt.c:1304
fbcon_modechanged+0x367/0x790 drivers/video/fbdev/core/fbcon.c:2980
fbcon_update_vcs+0x42/0x50 drivers/video/fbdev/core/fbcon.c:3038
fb_set_var+0xb32/0xdd0 drivers/video/fbdev/core/fbmem.c:1051
do_fb_ioctl+0x390/0x7d0 drivers/video/fbdev/core/fbmem.c:1104
fb_ioctl+0xe6/0x130 drivers/video/fbdev/core/fbmem.c:1180
vfs_ioctl fs/ioctl.c:47 [inline]
file_ioctl fs/ioctl.c:545 [inline]
do_vfs_ioctl+0x977/0x14e0 fs/ioctl.c:732
ksys_ioctl+0xab/0xd0 fs/ioctl.c:749
__do_sys_ioctl fs/ioctl.c:756 [inline]
__se_sys_ioctl fs/ioctl.c:754 [inline]
__x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:754
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 13273:
save_stack+0x23/0x90 mm/kasan/common.c:72
set_track mm/kasan/common.c:80 [inline]
kasan_set_free_info mm/kasan/common.c:335 [inline]
__kasan_slab_free+0x102/0x150 mm/kasan/common.c:474
kasan_slab_free+0xe/0x10 mm/kasan/common.c:483
__cache_free mm/slab.c:3426 [inline]
kfree+0x10a/0x2c0 mm/slab.c:3757
tomoyo_path_perm+0x389/0x430 security/tomoyo/file.c:840
tomoyo_path_symlink+0xaa/0xf0 security/tomoyo/tomoyo.c:206
security_path_symlink+0x10a/0x170 security/security.c:1053
do_symlinkat+0x137/0x290 fs/namei.c:4156
__do_sys_symlink fs/namei.c:4177 [inline]
__se_sys_symlink fs/namei.c:4175 [inline]
__x64_sys_symlink+0x59/0x80 fs/namei.c:4175
do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff8880a284cd80
which belongs to the cache kmalloc-32 of size 32
The buggy address is located 12 bytes inside of
32-byte region [ffff8880a284cd80, ffff8880a284cda0)
The buggy address belongs to the page:
page:ffffea00028a1300 refcount:1 mapcount:0 mapping:ffff8880aa4001c0
index:0xffff8880a284cfc1
raw: 00fffe0000000200 ffffea00025a5ac8 ffffea0002a010c8 ffff8880aa4001c0
raw: ffff8880a284cfc1 ffff8880a284c000 0000000100000037 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8880a284cc80: 06 fc fc fc fc fc fc fc 06 fc fc fc fc fc fc fc
ffff8880a284cd00: 06 fc fc fc fc fc fc fc fb fb fb fb fc fc fc fc
> ffff8880a284cd80: 00 04 fc fc fc fc fc fc 06 fc fc fc fc fc fc fc
^
ffff8880a284ce00: 06 fc fc fc fc fc fc fc 06 fc fc fc fc fc fc fc
ffff8880a284ce80: 06 fc fc fc fc fc fc fc fb fb fb fb 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 syzkaller@googlegroups.com.

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

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