KASAN: vmalloc-out-of-bounds Write in bitfill_aligned

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    63de3747 Merge tag 'tag-chrome-platform-for-v5.5' of git:/..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1040fc41e00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=1d189d07c6717979
dashboard link: https://syzkaller.appspot.com/bug?extid=e5fd3e65515b48c02a30
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+e5fd3e65515b48c02a30 at syzkaller.appspotmail.com

==================================================================
BUG: KASAN: vmalloc-out-of-bounds in bitfill_aligned  
drivers/video/fbdev/core/sysfillrect.c:54 [inline]
BUG: KASAN: vmalloc-out-of-bounds in bitfill_aligned+0x356/0x410  
drivers/video/fbdev/core/sysfillrect.c:25
Write of size 8 at addr ffffc90008b11000 by task syz-executor.2/9476

CPU: 2 PID: 9476 Comm: syz-executor.2 Not tainted 5.4.0-syzkaller #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS  
rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014
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_store8_noabort+0x17/0x20 mm/kasan/generic_report.c:140
  bitfill_aligned drivers/video/fbdev/core/sysfillrect.c:54 [inline]
  bitfill_aligned+0x356/0x410 drivers/video/fbdev/core/sysfillrect.c:25
  sys_fillrect+0x421/0x7c0 drivers/video/fbdev/core/sysfillrect.c:291
  drm_fb_helper_sys_fillrect+0x21/0x190 drivers/gpu/drm/drm_fb_helper.c:736
  bit_clear_margins+0x30b/0x530 drivers/video/fbdev/core/bitblit.c:232
  fbcon_clear_margins+0x1e9/0x250 drivers/video/fbdev/core/fbcon.c:1372
  fbcon_switch+0xd7f/0x17f0 drivers/video/fbdev/core/fbcon.c:2354
  redraw_screen+0x2b6/0x7d0 drivers/tty/vt/vt.c:997
  fbcon_modechanged+0x5c3/0x790 drivers/video/fbdev/core/fbcon.c:2991
  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: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: 0033:0x45a759
Code: bd b1 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 8b b1 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f8280324c88 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 000000000072bf00 RCX: 000000000045a759
RDX: 0000000020000040 RSI: 0000000000004601 RDI: 0000000000000003
RBP: 0000000000000003 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f82803256d4
R13: 00000000004a9e78 R14: 00000000006ec2d8 R15: 00000000ffffffff


Memory state around the buggy address:
  ffffc90008b10f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  ffffc90008b10f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> ffffc90008b11000: f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9
                    ^
  ffffc90008b11080: f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9
  ffffc90008b11100: f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9
==================================================================


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