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

[syzbot]

syzbot has found a reproducer for the following crash on:

HEAD commit:    510c9788 Merge tag 'Wimplicit-fallthrough-5.5-rc2' of git:..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16b8c1b6e00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=79f79de2a27d3e3d
dashboard link: https://syzkaller.appspot.com/bug?extid=6a8d618862e1fc55313d
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14f695a9e00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=158e0d1ee00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+6a8d618862e1fc55313d@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 9793b067 P4D 9793b067 PUD 0
Oops: 0002 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 9320 Comm: syz-executor815 Not tainted 5.5.0-rc1-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:insert_char+0x23d/0x400 drivers/tty/vt/vt.c:840
Code: 00 fc ff df 48 89 fa 48 c1 ea 03 0f b6 04 02 84 c0 74 08 3c 01 0f 8e  
1e 01 00 00 d1 eb 41 0f b7 85 c8 03 00 00 4c 89 ff 89 d9 <f3> 66 ab 49 8d  
bd 78 04 00 00 48 b8 00 00 00 00 00 fc ff df 48 89
RSP: 0018:ffffc90001dd7858 EFLAGS: 00010202
RAX: 0000000000000720 RBX: 0000000000000001 RCX: 0000000000000001
RDX: 1ffff11011e78679 RSI: 000000010000000e RDI: 000000010000000e
RBP: ffffc90001dd78a0 R08: ffff888095018400 R09: ffff888095018c90
R10: fffffbfff14f3388 R11: ffffffff8a799c47 R12: 0000000000000000
R13: ffff88808f3c3000 R14: ffff88808f3c3334 R15: 000000010000000e
FS:  00000000021de880(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000010000000e CR3: 00000000a91a0000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 csi_at drivers/tty/vt/vt.c:1964 [inline]
 do_con_trol+0x41a6/0x61b0 drivers/tty/vt/vt.c:2431
 do_con_write.part.0+0xfd9/0x1ef0 drivers/tty/vt/vt.c:2797
 do_con_write drivers/tty/vt/vt.c:2565 [inline]
 con_write+0x46/0xd0 drivers/tty/vt/vt.c:3135
 process_output_block drivers/tty/n_tty.c:595 [inline]
 n_tty_write+0x40e/0x1080 drivers/tty/n_tty.c:2333
 do_tty_write drivers/tty/tty_io.c:962 [inline]
 tty_write+0x496/0x7f0 drivers/tty/tty_io.c:1046
 __vfs_write+0x8a/0x110 fs/read_write.c:494
 vfs_write+0x268/0x5d0 fs/read_write.c:558
 ksys_write+0x14f/0x290 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+0x73/0xb0 fs/read_write.c:620
 do_syscall_64+0xfa/0x790 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:00007ffd7f172088 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 609e8edb17a11e0f ]---
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:insert_char+0x23d/0x400 drivers/tty/vt/vt.c:840
Code: 00 fc ff df 48 89 fa 48 c1 ea 03 0f b6 04 02 84 c0 74 08 3c 01 0f 8e  
1e 01 00 00 d1 eb 41 0f b7 85 c8 03 00 00 4c 89 ff 89 d9 <f3> 66 ab 49 8d  
bd 78 04 00 00 48 b8 00 00 00 00 00 fc ff df 48 89
RSP: 0018:ffffc90001dd7858 EFLAGS: 00010202
RAX: 0000000000000720 RBX: 0000000000000001 RCX: 0000000000000001
RDX: 1ffff11011e78679 RSI: 000000010000000e RDI: 000000010000000e
RBP: ffffc90001dd78a0 R08: ffff888095018400 R09: ffff888095018c90
R10: fffffbfff14f3388 R11: ffffffff8a799c47 R12: 0000000000000000
R13: ffff88808f3c3000 R14: ffff88808f3c3334 R15: 000000010000000e
FS:  00000000021de880(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000010000000e CR3: 00000000a91a0000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400