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SubjectKASAN: global-out-of-bounds Read in fbcon_get_font
From
Hello,

syzbot found the following crash on:

HEAD commit: 6cf8298d Add linux-next specific files for 20191209
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=168bbb7ae00000
kernel config: https://syzkaller.appspot.com/x/.config?x=682fc0ce6c86e3c7
dashboard link: https://syzkaller.appspot.com/bug?extid=29d4ed7f3bdedf2aa2fd
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=12fff061e00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+29d4ed7f3bdedf2aa2fd@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: global-out-of-bounds in memcpy include/linux/string.h:425
[inline]
BUG: KASAN: global-out-of-bounds in fbcon_get_font+0x2b2/0x5e0
drivers/video/fbdev/core/fbcon.c:2465
Read of size 32 at addr ffffffff88729d80 by task syz-executor.3/9100

CPU: 1 PID: 9100 Comm: syz-executor.3 Not tainted
5.5.0-rc1-next-20191209-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+0x5/0x30b 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:425 [inline]
fbcon_get_font+0x2b2/0x5e0 drivers/video/fbdev/core/fbcon.c:2465
con_font_get drivers/tty/vt/vt.c:4446 [inline]
con_font_op+0x20b/0x1270 drivers/tty/vt/vt.c:4605
vt_ioctl+0xd2e/0x26d0 drivers/tty/vt/vt_ioctl.c:913
tty_ioctl+0xa37/0x14f0 drivers/tty/tty_io.c:2660
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: 0033:0x45a6f9
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:00007f30314dcc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000045a6f9
RDX: 0000000000713000 RSI: 0000000000004b60 RDI: 0000000000000004
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f30314dd6d4
R13: 00000000004c6d87 R14: 00000000004dd3e0 R15: 00000000ffffffff

The buggy address belongs to the variable:
fontdata_8x16+0x1000/0x1120

Memory state around the buggy address:
ffffffff88729c80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffffffff88729d00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> ffffffff88729d80: fa fa fa fa 06 fa fa fa fa fa fa fa 05 fa fa fa
^
ffffffff88729e00: fa fa fa fa 06 fa fa fa fa fa fa fa 00 00 03 fa
ffffffff88729e80: fa fa fa fa 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================


---
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:
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syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

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