KASAN: global-out-of-bounds Read in vga16fb_imageblit

[syzbot <syzbot+69fbd3e01470f169c8c4@syzkaller.appspotmail.com>]

Hello,

syzbot found the following crash on:

HEAD commit:    596cf45c Merge branch 'akpm' (patches from Andrew)
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17be842ee00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=7d8ab2e0e09c2a82
dashboard link: https://syzkaller.appspot.com/bug?extid=69fbd3e01470f169c8c4
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=159c2861e00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16b5d59ce00000

Bisection is inconclusive: the bug happens on the oldest tested release.

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=161f2cdee00000
console output: https://syzkaller.appspot.com/x/log.txt?x=111f2cdee00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+69fbd3e01470f169c8c4@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: global-out-of-bounds in vga_8planes_imageblit  
drivers/video/fbdev/vga16fb.c:1140 [inline]
BUG: KASAN: global-out-of-bounds in vga_imageblit_expand  
drivers/video/fbdev/vga16fb.c:1203 [inline]
BUG: KASAN: global-out-of-bounds in vga16fb_imageblit+0x1c8b/0x2200  
drivers/video/fbdev/vga16fb.c:1260
Read of size 2 at addr ffffffff8874be58 by task syz-executor421/8988

CPU: 0 PID: 8988 Comm: syz-executor421 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:638
  __asan_report_load2_noabort+0x14/0x20 mm/kasan/generic_report.c:133
  vga_8planes_imageblit drivers/video/fbdev/vga16fb.c:1140 [inline]
  vga_imageblit_expand drivers/video/fbdev/vga16fb.c:1203 [inline]
  vga16fb_imageblit+0x1c8b/0x2200 drivers/video/fbdev/vga16fb.c:1260
  soft_cursor+0x4fb/0xa30 drivers/video/fbdev/core/softcursor.c:74
  bit_cursor+0x12fc/0x1a60 drivers/video/fbdev/core/bitblit.c:386
  fbcon_cursor+0x487/0x660 drivers/video/fbdev/core/fbcon.c:1402
  hide_cursor+0x9d/0x2b0 drivers/tty/vt/vt.c:895
  redraw_screen+0x60b/0x7d0 drivers/tty/vt/vt.c:988
  vc_do_resize+0x10c9/0x1460 drivers/tty/vt/vt.c:1284
  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:539 [inline]
  do_vfs_ioctl+0xdb6/0x13e0 fs/ioctl.c:726
  ksys_ioctl+0xab/0xd0 fs/ioctl.c:743
  __do_sys_ioctl fs/ioctl.c:750 [inline]
  __se_sys_ioctl fs/ioctl.c:748 [inline]
  __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:748
  do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
  entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x440309
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 fb 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffe5b970878 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000440309
RDX: 0000000020000100 RSI: 0000000000004601 RDI: 0000000000000003
RBP: 00000000006ca018 R08: 0000000000000000 R09: 00000000004002c8
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000401b90
R13: 0000000000401c20 R14: 0000000000000000 R15: 0000000000000000

The buggy address belongs to the variable:
  transl_h+0x38/0x40

Memory state around the buggy address:
  ffffffff8874bd00: 00 00 00 00 fa fa fa fa 00 00 00 00 fa fa fa fa
  ffffffff8874bd80: 00 00 00 00 00 fa fa fa fa fa fa fa 04 fa fa fa
> ffffffff8874be00: fa fa fa fa 00 00 00 00 fa fa fa fa 00 00 00 00
                                                     ^
  ffffffff8874be80: fa fa fa fa 00 01 fa fa fa fa fa fa 00 00 00 04
  ffffffff8874bf00: fa fa fa fa 00 00 04 fa fa fa fa fa 00 00 00 00
==================================================================


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