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

syzbot found the following issue on:

HEAD commit: 8eb858df Add linux-next specific files for 20200819
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1158a00e900000
kernel config: https://syzkaller.appspot.com/x/.config?x=cd187ef624ef7f02
dashboard link: https://syzkaller.appspot.com/bug?extid=b38b1ef6edf0c74a8d97
compiler: gcc (GCC) 10.1.0-syz 20200507
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=146a5589900000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=165aa636900000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b38b1ef6edf0c74a8d97@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: global-out-of-bounds in fbcon_resize+0x781/0x810 drivers/video/fbdev/core/fbcon.c:2206
Read of size 4 at addr ffffffff8896d418 by task syz-executor732/6868

CPU: 0 PID: 6868 Comm: syz-executor732 Not tainted 5.9.0-rc1-next-20200819-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+0x18f/0x20d lib/dump_stack.c:118
print_address_description.constprop.0.cold+0x5/0x497 mm/kasan/report.c:383
__kasan_report mm/kasan/report.c:513 [inline]
kasan_report.cold+0x1f/0x37 mm/kasan/report.c:530
fbcon_resize+0x781/0x810 drivers/video/fbdev/core/fbcon.c:2206
resize_screen drivers/tty/vt/vt.c:1175 [inline]
vc_do_resize+0x535/0x1150 drivers/tty/vt/vt.c:1246
vt_ioctl+0x11d2/0x2cc0 drivers/tty/vt/vt_ioctl.c:1025
tty_ioctl+0x1019/0x15f0 drivers/tty/tty_io.c:2656
vfs_ioctl fs/ioctl.c:48 [inline]
__do_sys_ioctl fs/ioctl.c:753 [inline]
__se_sys_ioctl fs/ioctl.c:739 [inline]
__x64_sys_ioctl+0x193/0x200 fs/ioctl.c:739
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x440329
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 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 0f 83 db 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffc8ff997d8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000440329
RDX: 0000000020000040 RSI: 0000000000005609 RDI: 0000000000000004
RBP: 00000000006ca018 R08: 000000000000000d R09: 00000000004002c8
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000401b90
R13: 0000000000401c20 R14: 0000000000000000 R15: 0000000000000000

The buggy address belongs to the variable:
font_vga_8x16+0x58/0x60

Memory state around the buggy address:
ffffffff8896d300: 00 00 00 00 00 00 00 00 00 00 00 00 f9 f9 f9 f9
ffffffff8896d380: 00 f9 f9 f9 f9 f9 f9 f9 00 00 00 00 00 f9 f9 f9
>ffffffff8896d400: f9 f9 f9 f9 00 00 00 00 00 00 00 00 00 00 00 00
^
ffffffff8896d480: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffffffff8896d500: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================


---
This report 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 issue. See:
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syzbot can test patches for this issue, for details see:
https://goo.gl/tpsmEJ#testing-patches

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