Re: general protection fault in nf_ct_gre_keymap_flush

[syzbot]

syzbot has found a reproducer for the following crash on:

HEAD commit:    5b74ce505631 Add linux-next specific files for 20190123
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1137e1b7400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d4d5d672c7c71240
dashboard link: https://syzkaller.appspot.com/bug?extid=fcee88b2d87f0539dfe9
compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=165f80c0c00000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+fcee88b2d87f0539dfe9@xxxxxxxxxxxxxxxxxxxxxxxxx

kasan: CONFIG_KASAN_INLINE enabled
kasan: GPF could be caused by NULL-ptr deref or user memory access
general protection fault: 0000 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 8342 Comm: syz-executor2 Not tainted 5.0.0-rc3-next-20190123 #18
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
RIP: 0010:nf_ct_gre_keymap_flush+0xb9/0x2f0  
net/netfilter/nf_conntrack_proto_gre.c:65
Code: 4c 89 f0 48 c1 e8 03 42 80 3c 20 00 0f 85 2b 02 00 00 4c 8b bb f8 16  
00 00 48 b8 00 00 00 00 00 fc ff df 4c 89 f9 48 c1 e9 03 <80> 3c 01 00 0f  
85 fc 01 00 00 4c 3b bd 68 ff ff ff 4d 8b 27 0f 84
RSP: 0018:ffff8880743eeef8 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: ffff888074c10240 RCX: 0000000000000000
RDX: 1ffffffff146dff2 RSI: 0000000000000004 RDI: ffff8880743eee60
RBP: ffff8880743eefa8 R08: 1ffff1100e87ddcc R09: ffffed100e87ddcd
R10: ffffed100e87ddcc R11: 0000000000000003 R12: dffffc0000000000
R13: ffff8880743ef0b8 R14: ffff888074c11938 R15: 0000000000000000
FS:  00007f7ceb928700(0000) GS:ffff8880ae700000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020000000 CR3: 00000000a089b000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 nf_conntrack_proto_pernet_fini+0x16/0x1a  
net/netfilter/nf_conntrack_proto.c:617
 nf_conntrack_cleanup_net_list+0x204/0x330  
net/netfilter/nf_conntrack_core.c:2183
 nf_conntrack_cleanup_net+0x1c5/0x270 net/netfilter/nf_conntrack_core.c:2156
 nf_conntrack_pernet_init net/netfilter/nf_conntrack_standalone.c:1122  
[inline]
 nf_conntrack_pernet_init+0xc3f/0xf00  
net/netfilter/nf_conntrack_standalone.c:1091
 ops_init+0x109/0x5d0 net/core/net_namespace.c:129
 setup_net+0x38f/0x940 net/core/net_namespace.c:314
 copy_net_ns+0x2ae/0x4b0 net/core/net_namespace.c:437
 create_new_namespaces+0x4ce/0x930 kernel/nsproxy.c:107
 copy_namespaces+0x3ff/0x4d0 kernel/nsproxy.c:165
 copy_process+0x4a2d/0x8890 kernel/fork.c:1920
 _do_fork+0x1a9/0x1170 kernel/fork.c:2227
 __do_sys_clone kernel/fork.c:2334 [inline]
 __se_sys_clone kernel/fork.c:2328 [inline]
 __x64_sys_clone+0xbf/0x150 kernel/fork.c:2328
 do_syscall_64+0x1a3/0x800 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x458099
Code: 6d b7 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 3b b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f7ceb927c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000038
RAX: ffffffffffffffda RBX: 0000000000000005 RCX: 0000000000458099
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000070024103
RBP: 000000000073bfa0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f7ceb9286d4
R13: 00000000004be480 R14: 00000000004ce960 R15: 00000000ffffffff
Modules linked in:
---[ end trace cdb65ca986e98ff1 ]---
RIP: 0010:nf_ct_gre_keymap_flush+0xb9/0x2f0  
net/netfilter/nf_conntrack_proto_gre.c:65
Code: 4c 89 f0 48 c1 e8 03 42 80 3c 20 00 0f 85 2b 02 00 00 4c 8b bb f8 16  
00 00 48 b8 00 00 00 00 00 fc ff df 4c 89 f9 48 c1 e9 03 <80> 3c 01 00 0f  
85 fc 01 00 00 4c 3b bd 68 ff ff ff 4d 8b 27 0f 84
RSP: 0018:ffff8880743eeef8 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: ffff888074c10240 RCX: 0000000000000000
RDX: 1ffffffff146dff2 RSI: 0000000000000004 RDI: ffff8880743eee60
RBP: ffff8880743eefa8 R08: 1ffff1100e87ddcc R09: ffffed100e87ddcd
R10: ffffed100e87ddcc R11: 0000000000000003 R12: dffffc0000000000
R13: ffff8880743ef0b8 R14: ffff888074c11938 R15: 0000000000000000
FS:  00007f7ceb928700(0000) GS:ffff8880ae700000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000020000000 CR3: 00000000a089b000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400