stack segment fault in redraw_screen

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    b2768df2 Merge branch 'for-linus' of git://git.kernel.org/..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17bb4fc8100000
kernel config:  https://syzkaller.appspot.com/x/.config?x=78a7d8adda44b4b
dashboard link: https://syzkaller.appspot.com/bug?extid=a2ae636def3ebbeae7c1
compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)

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+a2ae636def3ebbeae7c1@xxxxxxxxxxxxxxxxxxxxxxxxx

stack segment: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 5 Comm: kworker/0:0 Not tainted 5.7.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events console_callback
RIP: 0010:add_softcursor drivers/tty/vt/vt.c:865 [inline]
RIP: 0010:set_cursor drivers/tty/vt/vt.c:907 [inline]
RIP: 0010:redraw_screen+0xe44/0x16f0 drivers/tty/vt/vt.c:1025
Code: 00 48 89 d8 48 c1 e8 03 80 3c 28 00 74 08 48 89 df e8 e0 9c b6 fd 4c 8b 2b 4c 89 ed 48 c1 ed 03 48 bb 00 00 00 00 00 fc ff df <8a> 44 1d 00 84 c0 0f 85 90 07 00 00 45 0f b7 75 00 4c 89 64 24 18
RSP: 0018:ffffc90000cbfbc0 EFLAGS: 00010206
RAX: 1ffff1100860827e RBX: dffffc0000000000 RCX: ffff8880a99a4140
RDX: 0000000000000000 RSI: 00000000000000c0 RDI: ffff888043041000
RBP: 000000001fffffee R08: ffffffff83faa792 R09: ffffed10148b8a84
R10: ffffed10148b8a84 R11: 0000000000000000 R12: ffff888043041000
R13: 00000000ffffff70 R14: 1ffff1100860829a R15: 0000000000000001
FS:  0000000000000000(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00005633a6f64f08 CR3: 00000000a2ddc000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 complete_change_console+0xb1/0x720 drivers/tty/vt/vt_ioctl.c:1274
 console_callback+0x106/0x330 drivers/tty/vt/vt.c:2844
 process_one_work+0x76e/0xfd0 kernel/workqueue.c:2268
 worker_thread+0xa7f/0x1450 kernel/workqueue.c:2414
 kthread+0x353/0x380 kernel/kthread.c:268
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
Modules linked in:
---[ end trace 2eb94778444607de ]---
RIP: 0010:add_softcursor drivers/tty/vt/vt.c:865 [inline]
RIP: 0010:set_cursor drivers/tty/vt/vt.c:907 [inline]
RIP: 0010:redraw_screen+0xe44/0x16f0 drivers/tty/vt/vt.c:1025
Code: 00 48 89 d8 48 c1 e8 03 80 3c 28 00 74 08 48 89 df e8 e0 9c b6 fd 4c 8b 2b 4c 89 ed 48 c1 ed 03 48 bb 00 00 00 00 00 fc ff df <8a> 44 1d 00 84 c0 0f 85 90 07 00 00 45 0f b7 75 00 4c 89 64 24 18
RSP: 0018:ffffc90000cbfbc0 EFLAGS: 00010206
RAX: 1ffff1100860827e RBX: dffffc0000000000 RCX: ffff8880a99a4140
RDX: 0000000000000000 RSI: 00000000000000c0 RDI: ffff888043041000
RBP: 000000001fffffee R08: ffffffff83faa792 R09: ffffed10148b8a84
R10: ffffed10148b8a84 R11: 0000000000000000 R12: ffff888043041000
R13: 00000000ffffff70 R14: 1ffff1100860829a R15: 0000000000000001
FS:  0000000000000000(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00005633a6f64f08 CR3: 00000000a2ddc000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


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