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Subjectgeneral protection fault in redraw_screen
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Hello,

syzbot found the following crash on:

HEAD commit: 359c92c0 Merge tag 'dax-fixes-5.6-rc1' of git://git.kernel..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15a432a1e00000
kernel config: https://syzkaller.appspot.com/x/.config?x=6780df5a5f208964
dashboard link: https://syzkaller.appspot.com/bug?extid=4a5a3604a566ede699b9
compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16d2e2a1e00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11ff82e6e00000

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

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=1701cfa5e00000
final crash: https://syzkaller.appspot.com/x/report.txt?x=1481cfa5e00000
console output: https://syzkaller.appspot.com/x/log.txt?x=1081cfa5e00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+4a5a3604a566ede699b9@syzkaller.appspotmail.com

general protection fault, probably for non-canonical address 0xdffffc0020000001: 0000 [#1] PREEMPT SMP KASAN
KASAN: probably user-memory-access in range [0x0000000100000008-0x000000010000000f]
CPU: 1 PID: 2936 Comm: kworker/1:49 Not tainted 5.6.0-rc1-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:906 [inline]
RIP: 0010:redraw_screen+0xf1c/0x1830 drivers/tty/vt/vt.c:1013
Code: 00 00 00 00 00 fc ff df 80 3c 10 00 74 12 48 89 df e8 68 2f b5 fd 48 ba 00 00 00 00 00 fc ff df 4c 8b 2b 4d 89 ec 49 c1 ec 03 <41> 8a 04 14 84 c0 0f 85 ef 07 00 00 45 0f b7 75 00 48 8b 45 a0 48
RSP: 0018:ffffc900085b7b38 EFLAGS: 00010203
RAX: 1ffff110127e0c74 RBX: ffff888093f063a0 RCX: ffff88809e516640
RDX: dffffc0000000000 RSI: 00000000000000c0 RDI: 0000000000000000
RBP: ffffc900085b7bc0 R08: ffffffff83fef5be R09: ffffed10431c9484
R10: ffffed10431c9484 R11: 0000000000000000 R12: 0000000020000001
R13: 000000010000000c R14: 000000000000001f R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff8880aeb00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000455300 CR3: 000000008c51f000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
complete_change_console+0xb9/0x750 drivers/tty/vt/vt_ioctl.c:1264
change_console+0x2d8/0x450 drivers/tty/vt/vt_ioctl.c:1389
console_callback+0x104/0x330 drivers/tty/vt/vt.c:2824
process_one_work+0x7f5/0x10f0 kernel/workqueue.c:2264
worker_thread+0xbbc/0x1630 kernel/workqueue.c:2410
kthread+0x332/0x350 kernel/kthread.c:255
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
Modules linked in:
---[ end trace f61ede7c24462fc9 ]---
RIP: 0010:add_softcursor drivers/tty/vt/vt.c:865 [inline]
RIP: 0010:set_cursor drivers/tty/vt/vt.c:906 [inline]
RIP: 0010:redraw_screen+0xf1c/0x1830 drivers/tty/vt/vt.c:1013
Code: 00 00 00 00 00 fc ff df 80 3c 10 00 74 12 48 89 df e8 68 2f b5 fd 48 ba 00 00 00 00 00 fc ff df 4c 8b 2b 4d 89 ec 49 c1 ec 03 <41> 8a 04 14 84 c0 0f 85 ef 07 00 00 45 0f b7 75 00 48 8b 45 a0 48
RSP: 0018:ffffc900085b7b38 EFLAGS: 00010203
RAX: 1ffff110127e0c74 RBX: ffff888093f063a0 RCX: ffff88809e516640
RDX: dffffc0000000000 RSI: 00000000000000c0 RDI: 0000000000000000
RBP: ffffc900085b7bc0 R08: ffffffff83fef5be R09: ffffed10431c9484
R10: ffffed10431c9484 R11: 0000000000000000 R12: 0000000020000001
R13: 000000010000000c R14: 000000000000001f R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff8880aeb00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000455300 CR3: 000000008c51f000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this bug report. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
For information about bisection process see: https://goo.gl/tpsmEJ#bisection
syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

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