BUG: unable to handle kernel NULL pointer dereference in rds_bind

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    f4b752a6 mlx4: fix spelling mistake "veify" -> "verify"
git tree:       net
console output: https://syzkaller.appspot.com/x/log.txt?x=16cbebe6600000
kernel config:  https://syzkaller.appspot.com/x/.config?x=b89bb446a3faaba4
dashboard link: https://syzkaller.appspot.com/bug?extid=fae39afd2101a17ec624
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10753bc1600000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=111dfc11600000

The bug was bisected to:

commit b9a1e627405d68d475a3c1f35e685ccfb5bbe668
Author: Cong Wang <xiyou.wangcong@xxxxxxxxx>
Date:   Thu Jul 4 00:21:13 2019 +0000

    hsr: implement dellink to clean up resources

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=11005fc1600000
final crash:    https://syzkaller.appspot.com/x/report.txt?x=13005fc1600000
console output: https://syzkaller.appspot.com/x/log.txt?x=15005fc1600000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+fae39afd2101a17ec624@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: b9a1e627405d ("hsr: implement dellink to clean up resources")

BUG: kernel NULL pointer dereference, address: 0000000000000000
#PF: supervisor instruction fetch in kernel mode
#PF: error_code(0x0010) - not-present page
PGD 9fef0067 P4D 9fef0067 PUD 9060d067 PMD 0
Oops: 0010 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 9884 Comm: syz-executor453 Not tainted 5.3.0-rc7+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
RIP: 0010:0x0
Code: Bad RIP value.
RSP: 0018:ffff8880a7c6fcd8 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: ffffffff8992bfe0 RCX: ffffffff86b9b636
RDX: 0000000000000000 RSI: ffff8880a7c6fd40 RDI: ffffffff897830c0
RBP: ffff8880a7c6fda8 R08: ffff888093150558 R09: 0000000000000000
R10: fffffbfff134af9f R11: ffff88809a008040 R12: ffff888093150080
R13: ffffffff897830c0 R14: 0000000000000000 R15: ffff8880a7c6fd40
FS:  000055555738a880(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffffffffd6 CR3: 000000008f04a000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 rds_bind+0x420/0x800 net/rds/bind.c:247
 __sys_bind+0x239/0x290 net/socket.c:1647
 __do_sys_bind net/socket.c:1658 [inline]
 __se_sys_bind net/socket.c:1656 [inline]
 __x64_sys_bind+0x73/0xb0 net/socket.c:1656
 do_syscall_64+0xfd/0x6a0 arch/x86/entry/common.c:296
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4412b9
Code: e8 ac e8 ff ff 48 83 c4 18 c3 0f 1f 80 00 00 00 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 eb 08 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007ffc7c28b228 EFLAGS: 00000246 ORIG_RAX: 0000000000000031
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00000000004412b9
RDX: 0000000000000010 RSI: 0000000020000200 RDI: 0000000000000003
RBP: 00000000006cb018 R08: 00000000004002c8 R09: 00000000004002c8
R10: 00000000004002c8 R11: 0000000000000246 R12: 0000000000402030
R13: 00000000004020c0 R14: 0000000000000000 R15: 0000000000000000
Modules linked in:
CR2: 0000000000000000
---[ end trace b47a1983319ea52a ]---
RIP: 0010:0x0
Code: Bad RIP value.
RSP: 0018:ffff8880a7c6fcd8 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: ffffffff8992bfe0 RCX: ffffffff86b9b636
RDX: 0000000000000000 RSI: ffff8880a7c6fd40 RDI: ffffffff897830c0
RBP: ffff8880a7c6fda8 R08: ffff888093150558 R09: 0000000000000000
R10: fffffbfff134af9f R11: ffff88809a008040 R12: ffff888093150080
R13: ffffffff897830c0 R14: 0000000000000000 R15: ffff8880a7c6fd40
FS:  000055555738a880(0000) GS:ffff8880ae900000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000004bf788 CR3: 000000008f04a000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


---
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