BUG: kernel NULL pointer dereference, address: 0000000000000002
#PF: supervisor write access in kernel mode
#PF: error_code(0x0002) - not-present page
PGD 8f649067 P4D 8f649067 PUD 9ac73067 PMD 0 
Oops: 0002 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 24496 Comm: syz-executor.4 Not tainted 5.5.0-rc2-next-20191219-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:writeb arch/x86/include/asm/io.h:65 [inline]
RIP: 0010:mem_serial_out+0x70/0x90 drivers/tty/serial/8250/8250_port.c:408
Code: e9 00 00 00 49 8d 7c 24 40 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 d3 e3 80 3c 02 00 75 19 48 63 db 49 03 5c 24 40 <44> 88 2b 5b 41 5c 41 5d 5d c3 e8 c1 6f ce fd eb c0 e8 1a 70 ce fd
RSP: 0018:ffffc90005407a78 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: 0000000000000002 RCX: 0000000000000000
RDX: 1ffffffff18223e3 RSI: ffffffff83e4cd86 RDI: ffffffff8c111f18
RBP: ffffc90005407a90 R08: ffff8880a7494640 R09: ffffed104311e1c6
R10: ffffed104311e1c5 R11: ffff8882188f0e2b R12: ffffffff8c111ed8
R13: 0000000000000001 R14: 0000000000000100 R15: 0000000000000002
FS:  00007f43438a1700(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000002 CR3: 00000000a80c1000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 serial_out drivers/tty/serial/8250/8250.h:118 [inline]
 serial8250_clear_fifos.part.0+0x3a/0xb0 drivers/tty/serial/8250/8250_port.c:557
 serial8250_clear_fifos drivers/tty/serial/8250/8250_port.c:556 [inline]
 serial8250_do_startup+0x463/0x1d20 drivers/tty/serial/8250/8250_port.c:2121
 serial8250_startup+0x62/0x80 drivers/tty/serial/8250/8250_port.c:2329
 uart_port_startup drivers/tty/serial/serial_core.c:219 [inline]
 uart_startup drivers/tty/serial/serial_core.c:258 [inline]
 uart_startup+0x482/0xa90 drivers/tty/serial/serial_core.c:249
 uart_set_info drivers/tty/serial/serial_core.c:998 [inline]
 uart_set_info_user+0x13f1/0x1d20 drivers/tty/serial/serial_core.c:1023
 tty_tiocsserial drivers/tty/tty_io.c:2506 [inline]
 tty_ioctl+0xf60/0x14f0 drivers/tty/tty_io.c:2648
 vfs_ioctl fs/ioctl.c:47 [inline]
 ksys_ioctl+0x123/0x180 fs/ioctl.c:747
 __do_sys_ioctl fs/ioctl.c:756 [inline]
 __se_sys_ioctl fs/ioctl.c:754 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:754
 do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x45a919
Code: ad b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f43438a0c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 000000000045a919
RDX: 0000000020000240 RSI: 000000000000541f RDI: 0000000000000003
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f43438a16d4
R13: 00000000004c5e04 R14: 00000000004dc270 R15: 00000000ffffffff
Modules linked in:
CR2: 0000000000000002
---[ end trace fc2eb1ea66355c33 ]---
RIP: 0010:writeb arch/x86/include/asm/io.h:65 [inline]
RIP: 0010:mem_serial_out+0x70/0x90 drivers/tty/serial/8250/8250_port.c:408
Code: e9 00 00 00 49 8d 7c 24 40 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 d3 e3 80 3c 02 00 75 19 48 63 db 49 03 5c 24 40 <44> 88 2b 5b 41 5c 41 5d 5d c3 e8 c1 6f ce fd eb c0 e8 1a 70 ce fd
RSP: 0018:ffffc90005407a78 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: 0000000000000002 RCX: 0000000000000000
RDX: 1ffffffff18223e3 RSI: ffffffff83e4cd86 RDI: ffffffff8c111f18
RBP: ffffc90005407a90 R08: ffff8880a7494640 R09: ffffed104311e1c6
R10: ffffed104311e1c5 R11: ffff8882188f0e2b R12: ffffffff8c111ed8
R13: 0000000000000001 R14: 0000000000000100 R15: 0000000000000002
FS:  00007f43438a1700(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffee5f86268 CR3: 00000000a80c1000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400