BUG: kernel NULL pointer dereference, address: 0000000000000002
#PF: supervisor write access in kernel mode
#PF: error_code(0x0002) - not-present page
PGD 95648067 P4D 95648067 PUD a2ab2067 PMD 0 
Oops: 0002 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 9326 Comm: syz-executor434 Not tainted 5.5.0-rc2-next-20191218-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 f1 d5 ce fd eb c0 e8 4a d6 ce fd
RSP: 0018:ffffc9000207f8e8 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: 0000000000000002 RCX: 0000000000000000
RDX: 1ffffffff1821c96 RSI: ffffffff83e460b6 RDI: ffffffff8c10e4b0
RBP: ffffc9000207f900 R08: ffff888094784180 R09: ffffed10144ca1c6
R10: ffffed10144ca1c5 R11: ffff8880a2650e2b R12: ffffffff8c10e470
R13: 0000000000000001 R14: ffffffff8c10e470 R15: ffffffff8c10e5c8
FS:  0000000000a2a880(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000002 CR3: 00000000a7fbd000 CR4: 00000000001406f0
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+0x426/0x1cf0 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+0x479/0xa80 drivers/tty/serial/serial_core.c:249
 uart_set_info drivers/tty/serial/serial_core.c:998 [inline]
 uart_set_info_user+0x13b4/0x1cf0 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]
 file_ioctl fs/ioctl.c:545 [inline]
 do_vfs_ioctl+0x977/0x14e0 fs/ioctl.c:732
 ksys_ioctl+0xab/0xd0 fs/ioctl.c:749
 __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: 0033:0x440219
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 fb 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffe93fbc608 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000440219
RDX: 0000000020000240 RSI: 000000000000541f RDI: 0000000000000003
RBP: 00000000006ca018 R08: 0000000000000000 R09: 00000000004002c8
R10: 0000000000401b30 R11: 0000000000000246 R12: 0000000000401aa0
R13: 0000000000401b30 R14: 0000000000000000 R15: 0000000000000000
Modules linked in:
CR2: 0000000000000002
---[ end trace f4127722c55048a5 ]---
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 f1 d5 ce fd eb c0 e8 4a d6 ce fd
RSP: 0018:ffffc9000207f8e8 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: 0000000000000002 RCX: 0000000000000000
RDX: 1ffffffff1821c96 RSI: ffffffff83e460b6 RDI: ffffffff8c10e4b0
RBP: ffffc9000207f900 R08: ffff888094784180 R09: ffffed10144ca1c6
R10: ffffed10144ca1c5 R11: ffff8880a2650e2b R12: ffffffff8c10e470
R13: 0000000000000001 R14: ffffffff8c10e470 R15: ffffffff8c10e5c8
FS:  0000000000a2a880(0000) GS:ffff8880ae800000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000002 CR3: 00000000a7fbd000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400