KASAN: global-out-of-bounds Read in fb_pad_aligned_buffer

Sat Dec 7 21:58:08 UTC 2019

Hello,

syzbot found the following crash on:

HEAD commit:    ad910e36 pipe: fix poll/select race introduced by the pipe..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15483196e00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=318fa2bff8166d0d
dashboard link: https://syzkaller.appspot.com/bug?extid=0568d05e486eee0a1ba2
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+0568d05e486eee0a1ba2 at syzkaller.appspotmail.com

==================================================================
BUG: KASAN: global-out-of-bounds in __fb_pad_aligned_buffer  
include/linux/fb.h:655 [inline]
BUG: KASAN: global-out-of-bounds in fb_pad_aligned_buffer+0x138/0x160  
drivers/video/fbdev/core/fbmem.c:115
Read of size 1 at addr ffffffff887274d4 by task syz-executor.2/19900

CPU: 1 PID: 19900 Comm: syz-executor.2 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]
  fb_pad_aligned_buffer+0x138/0x160 drivers/video/fbdev/core/fbmem.c:115
  bit_putcs_aligned drivers/video/fbdev/core/bitblit.c:99 [inline]
  bit_putcs+0xd14/0xf10 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: 0033:0x45a6f9
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:00007fe2b58b1c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000045a6f9
RDX: 0000000020000000 RSI: 0000000000004b72 RDI: 0000000000000003
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007fe2b58b26d4
R13: 00000000004c382b R14: 00000000004d8d78 R15: 00000000ffffffff

The buggy address belongs to the variable:
  fontdata_8x16+0x1054/0x1120

Memory state around the buggy address:
  ffffffff88727380: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  ffffffff88727400: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> ffffffff88727480: fa fa fa fa 06 fa fa fa fa fa fa fa 05 fa fa fa
                                                  ^
  ffffffff88727500: fa fa fa fa 06 fa fa fa fa fa fa fa 00 00 03 fa
  ffffffff88727580: fa fa fa fa 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================

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