Re: BUG: unable to handle kernel paging request in do_con_write

[syzbot]

syzbot has found a reproducer for the following crash on:

HEAD commit:    8f8972a3 Merge tag 'mtd/fixes-for-5.5-rc7' of git://git.ke..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=130b73b9e00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=cfbb8fa33f49f9f3
dashboard link: https://syzkaller.appspot.com/bug?extid=d8cbeb7028cd2950172e
compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15ec4966e00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16b148d6e00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+d8cbeb7028cd2950172e@xxxxxxxxxxxxxxxxxxxxxxxxx

BUG: unable to handle page fault for address: 000000010000000e
#PF: supervisor write access in kernel mode
#PF: error_code(0x0002) - not-present page
PGD a98de067 P4D a98de067 PUD 0 
Oops: 0002 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 8686 Comm: syz-executor679 Not tainted 5.5.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:memset16 arch/x86/include/asm/string_64.h:25 [inline]
RIP: 0010:scr_memsetw include/linux/vt_buffer.h:36 [inline]
RIP: 0010:csi_K drivers/tty/vt/vt.c:1558 [inline]
RIP: 0010:do_con_trol drivers/tty/vt/vt.c:2370 [inline]
RIP: 0010:do_con_write+0x9f72/0xf360 drivers/tty/vt/vt.c:2797
Code: 00 00 00 00 00 fc ff df 8a 04 08 84 c0 0f 85 10 44 00 00 48 8b 84 24 a0 00 00 00 0f b7 00 44 89 f9 81 e1 ff ff ff 7f 4c 89 f7 <f3> 66 ab 48 b8 00 00 00 00 00 fc ff df 48 8b 4c 24 50 8a 04 01 84
RSP: 0018:ffffc900021f7880 EFLAGS: 00010202
RAX: 0000000000000720 RBX: 0000000000000000 RCX: 0000000000000001
RDX: 0000000000000000 RSI: ffffffff89239ed0 RDI: 000000010000000e
RBP: ffffc900021f7b68 R08: 0000000000000005 R09: ffffffff83fa1e48
R10: ffff8880a274c1c0 R11: 0000000000000003 R12: 0000000000000000
R13: dffffc0000000000 R14: 000000010000000e R15: 0000000000000001
FS:  0000000001545880(0000) GS:ffff8880aec00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000010000000e CR3: 0000000097629000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 con_write+0x25/0x40 drivers/tty/vt/vt.c:3135
 process_output_block drivers/tty/n_tty.c:595 [inline]
 n_tty_write+0xd0c/0x1200 drivers/tty/n_tty.c:2333
 do_tty_write drivers/tty/tty_io.c:962 [inline]
 tty_write+0x5a1/0x950 drivers/tty/tty_io.c:1046
 __vfs_write+0xb8/0x740 fs/read_write.c:494
 vfs_write+0x270/0x580 fs/read_write.c:558
 ksys_write+0x117/0x220 fs/read_write.c:611
 __do_sys_write fs/read_write.c:623 [inline]
 __se_sys_write fs/read_write.c:620 [inline]
 __x64_sys_write+0x7b/0x90 fs/read_write.c:620
 do_syscall_64+0xf7/0x1c0 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4404f9
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 5b 14 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffcc98f9338 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 00000000004404f9
RDX: 0000000000000078 RSI: 0000000020000000 RDI: 0000000000000004
RBP: 00000000006ca018 R08: 0000000000000000 R09: 00000000004002c8
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000401de0
R13: 0000000000401e70 R14: 0000000000000000 R15: 0000000000000000
Modules linked in:
CR2: 000000010000000e
---[ end trace f08a62f87bf81d1c ]---
RIP: 0010:memset16 arch/x86/include/asm/string_64.h:25 [inline]
RIP: 0010:scr_memsetw include/linux/vt_buffer.h:36 [inline]
RIP: 0010:csi_K drivers/tty/vt/vt.c:1558 [inline]
RIP: 0010:do_con_trol drivers/tty/vt/vt.c:2370 [inline]
RIP: 0010:do_con_write+0x9f72/0xf360 drivers/tty/vt/vt.c:2797
Code: 00 00 00 00 00 fc ff df 8a 04 08 84 c0 0f 85 10 44 00 00 48 8b 84 24 a0 00 00 00 0f b7 00 44 89 f9 81 e1 ff ff ff 7f 4c 89 f7 <f3> 66 ab 48 b8 00 00 00 00 00 fc ff df 48 8b 4c 24 50 8a 04 01 84
RSP: 0018:ffffc900021f7880 EFLAGS: 00010202
RAX: 0000000000000720 RBX: 0000000000000000 RCX: 0000000000000001
RDX: 0000000000000000 RSI: ffffffff89239ed0 RDI: 000000010000000e
RBP: ffffc900021f7b68 R08: 0000000000000005 R09: ffffffff83fa1e48
R10: ffff8880a274c1c0 R11: 0000000000000003 R12: 0000000000000000
R13: dffffc0000000000 R14: 000000010000000e R15: 0000000000000001
FS:  0000000001545880(0000) GS:ffff8880aec00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000010000000e CR3: 0000000097629000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400