Re: KASAN: global-out-of-bounds Read in bit_putcs

[syzbot]

syzbot has found a reproducer for the following crash on:

HEAD commit:    b0d4beaa Merge branch 'next.autofs' of git://git.kernel.or..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1015a90ee00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f07a23020fd7d21a
dashboard link: https://syzkaller.appspot.com/bug?extid=38a3699c7eaf165b97a6
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1795d941e00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+38a3699c7eaf165b97a6@xxxxxxxxxxxxxxxxxxxxxxxxx

==================================================================
BUG: KASAN: global-out-of-bounds in __fb_pad_aligned_buffer  
include/linux/fb.h:655 [inline]
BUG: KASAN: global-out-of-bounds in bit_putcs_aligned  
drivers/video/fbdev/core/bitblit.c:96 [inline]
BUG: KASAN: global-out-of-bounds in bit_putcs+0xd5d/0xf10  
drivers/video/fbdev/core/bitblit.c:185
Read of size 1 at addr ffffffff88726a41 by task syz-executor.5/9415

CPU: 1 PID: 9415 Comm: syz-executor.5 Not tainted 5.4.0-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
 __asan_report_load1_noabort+0x14/0x20 mm/kasan/generic_report.c:132
 __fb_pad_aligned_buffer include/linux/fb.h:655 [inline]
 bit_putcs_aligned drivers/video/fbdev/core/bitblit.c:96 [inline]
 bit_putcs+0xd5d/0xf10 drivers/video/fbdev/core/bitblit.c:185
 fbcon_putcs+0x33c/0x3e0 drivers/video/fbdev/core/fbcon.c:1353
 do_update_region+0x42b/0x6f0 drivers/tty/vt/vt.c:677
 redraw_screen+0x676/0x7d0 drivers/tty/vt/vt.c:1011
 fbcon_do_set_font+0x829/0x960 drivers/video/fbdev/core/fbcon.c:2605
 fbcon_copy_font+0x12c/0x190 drivers/video/fbdev/core/fbcon.c:2620
 con_font_copy drivers/tty/vt/vt.c:4594 [inline]
 con_font_op+0x6b2/0x1270 drivers/tty/vt/vt.c:4609
 vt_ioctl+0x181a/0x26d0 drivers/tty/vt/vt_ioctl.c:965
 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: 0033:0x45a679
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:00007f5b74dffc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000045a679
RDX: 0000000020000000 RSI: 0000000000004b72 RDI: 0000000000000005
RBP: 000000000075bfc8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f5b74e006d4
R13: 00000000004c37ab R14: 00000000004d8c38 R15: 00000000ffffffff

The buggy address belongs to the variable:
 oid_index+0xb01/0xb80

Memory state around the buggy address:
 ffffffff88726900: 00 00 02 fa fa fa fa fa 00 00 00 05 fa fa fa fa
 ffffffff88726980: 00 00 00 fa fa fa fa fa 00 00 00 00 00 01 fa fa
> ffffffff88726a00: fa fa fa fa 00 00 00 00 01 fa fa fa fa fa fa fa
                                           ^
 ffffffff88726a80: 00 00 00 00 fa fa fa fa 00 03 fa fa fa fa fa fa
 ffffffff88726b00: 04 fa fa fa fa fa fa fa 00 00 01 fa fa fa fa fa
==================================================================