divide error in fbcon_switch

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 76bb8b05 Merge tag 'kbuild-v5.5' of git://git.kernel.org/p..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1508781ee00000
kernel config: https://syzkaller.appspot.com/x/.config?x=dd226651cb0f364b
dashboard link: https://syzkaller.appspot.com/bug?extid=13013adc4a234406c29e
compiler: gcc (GCC) 9.0.0 20181231 (experimental)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=132b742ae00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1568f97ee00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+13013a...@syzkaller.appspotmail.com

divide error: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 12 Comm: kworker/0:1 Not tainted 5.4.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Workqueue: events console_callback
RIP: 0010:fbcon_update_softback drivers/video/fbdev/core/fbcon.c:378
[inline]
RIP: 0010:fbcon_switch+0x20d/0x17f0 drivers/video/fbdev/core/fbcon.c:2247
Code: a4 3b 08 4c 89 3d 33 a4 3b 08 38 d0 7c 08 84 d2 0f 85 48 13 00 00 41
8b 9d 3c 03 00 00 31 d2 bf 05 00 00 00 8b 05 f3 07 13 06 <f7> f3 41 89 c4
89 c6 e8 67 48 c3 fd 41 83 fc 05 0f 8e d7 0b 00 00
RSP: 0018:ffffc90000d2f9d8 EFLAGS: 00010246
RAX: 0000000000008000 RBX: 0000000000000000 RCX: ffffffff83b1b314
RDX: 0000000000000000 RSI: ffffffff83b1b322 RDI: 0000000000000005
RBP: ffffc90000d2fb68 R08: ffff8880a9a06300 R09: fffffbfff14b0ac8
R10: fffffbfff14b0ac7 R11: ffffffff8a58563b R12: 0000000000000000
R13: ffff88809e21f000 R14: ffff8880a40fc000 R15: ffff8880a3860000
FS: 0000000000000000(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fb4a5f9a000 CR3: 00000000a64af000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
redraw_screen+0x2b6/0x7d0 drivers/tty/vt/vt.c:997
complete_change_console+0x105/0x3a0 drivers/tty/vt/vt_ioctl.c:1264
change_console+0x19b/0x2c0 drivers/tty/vt/vt_ioctl.c:1389
console_callback+0x3a1/0x400 drivers/tty/vt/vt.c:2824
process_one_work+0x9af/0x1740 kernel/workqueue.c:2264
worker_thread+0x98/0xe40 kernel/workqueue.c:2410
kthread+0x361/0x430 kernel/kthread.c:255
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
Modules linked in:
---[ end trace 074c38236abce447 ]---
RIP: 0010:fbcon_update_softback drivers/video/fbdev/core/fbcon.c:378
[inline]
RIP: 0010:fbcon_switch+0x20d/0x17f0 drivers/video/fbdev/core/fbcon.c:2247
Code: a4 3b 08 4c 89 3d 33 a4 3b 08 38 d0 7c 08 84 d2 0f 85 48 13 00 00 41
8b 9d 3c 03 00 00 31 d2 bf 05 00 00 00 8b 05 f3 07 13 06 <f7> f3 41 89 c4
89 c6 e8 67 48 c3 fd 41 83 fc 05 0f 8e d7 0b 00 00
RSP: 0018:ffffc90000d2f9d8 EFLAGS: 00010246
RAX: 0000000000008000 RBX: 0000000000000000 RCX: ffffffff83b1b314
RDX: 0000000000000000 RSI: ffffffff83b1b322 RDI: 0000000000000005
RBP: ffffc90000d2fb68 R08: ffff8880a9a06300 R09: fffffbfff14b0ac8
R10: fffffbfff14b0ac7 R11: ffffffff8a58563b R12: 0000000000000000
R13: ffff88809e21f000 R14: ffff8880a40fc000 R15: ffff8880a3860000
FS: 0000000000000000(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fb4a5f9a000 CR3: 00000000a64af000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


---
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[syzbot]

syzbot suspects this issue was fixed by commit:

commit ce684552a266cb1c7cc2f7e623f38567adec6653
Author: Tetsuo Handa <penguin...@I-love.SAKURA.ne.jp>
Date: Sun Jul 12 11:10:12 2020 +0000

vt: Reject zero-sized screen buffer size.

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=155549c4900000
start commit: 76bb8b05 Merge tag 'kbuild-v5.5' of git://git.kernel.org/p..
git tree: upstream

kernel config: https://syzkaller.appspot.com/x/.config?x=dd226651cb0f364b
dashboard link: https://syzkaller.appspot.com/bug?extid=13013adc4a234406c29e

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=17d69aeae00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13fdcc2ae00000

If the result looks correct, please mark the issue as fixed by replying with:

#syz fix: vt: Reject zero-sized screen buffer size.

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

[Tetsuo Handa]

#syz dup: general protection fault in do_con_write