Re: BUG: unable to handle kernel NULL pointer dereference in do_syscall_64 (2)

[syzbot]

syzbot has found a reproducer for the following crash on:

HEAD commit:    b2e2a818 Add linux-next specific files for 20200406
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=14022a57e00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=595413e7170f444b
dashboard link: https://syzkaller.appspot.com/bug?extid=d6d57d324860c94d5836
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14873543e00000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13ea05cde00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+d6d57d324860c94d5836@xxxxxxxxxxxxxxxxxxxxxxxxx

IPVS: ftp: loaded support on port[0] = 21
BUG: kernel NULL pointer dereference, address: 0000000000000000
#PF: supervisor write access in kernel mode
#PF: error_code(0x0002) - not-present page
PGD 962b6067 P4D 962b6067 PUD 9441e067 PMD 0 
Oops: 0002 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 7058 Comm: syz-executor367 Not tainted 5.6.0-next-20200406-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
Code: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 <00> 00 7d 50 48 ba 00 00 00 00 00 fc ff df 48 89 f9 48 c1 e9 03 80
RSP: 0018:ffffc90001657f28 EFLAGS: 00010286
RAX: 0000000000000000 RBX: 0000000000000023 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff8163ea3d RDI: 0000000000000282
RBP: ffffc90001657f58 R08: ffff8880a9156440 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: ffffffff89949570 R14: 0000000000000000 R15: 0000000000000000
FS:  00000000015f5940(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 00000000962b7000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 entry_SYSCALL_64_after_hwframe+0x49/0xb3
RIP: 0033:0x4464b0
Code: c0 5b 5d c3 66 0f 1f 44 00 00 8b 04 24 48 83 c4 18 5b 5d c3 66 0f 1f 44 00 00 83 3d 61 cb 29 00 00 75 14 b8 23 00 00 00 0f 05 <48> 3d 01 f0 ff ff 0f 83 84 20 fc ff c3 48 83 ec 08 e8 5a 43 00 00
RSP: 002b:00007fffeb3290d8 EFLAGS: 00000246 ORIG_RAX: 0000000000000023
RAX: ffffffffffffffda RBX: 00007fffeb329140 RCX: 00000000004464b0
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00007fffeb3290e0
RBP: 0000000000000002 R08: 0000000000000001 R09: 00000000015f5940
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000000fb38
R13: 0000000000408a50 R14: 0000000000000000 R15: 0000000000000000
Modules linked in:
CR2: 0000000000000000
---[ end trace 07b78701f72ec477 ]---
RIP: 0010:do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
Code: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 <00> 00 7d 50 48 ba 00 00 00 00 00 fc ff df 48 89 f9 48 c1 e9 03 80
RSP: 0018:ffffc90001657f28 EFLAGS: 00010286
RAX: 0000000000000000 RBX: 0000000000000023 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffffffff8163ea3d RDI: 0000000000000282
RBP: ffffc90001657f58 R08: ffff8880a9156440 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: ffffffff89949570 R14: 0000000000000000 R15: 0000000000000000
FS:  00000000015f5940(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 00000000962b7000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400