Re: general protection fault in nf_ct_gre_keymap_flush

[syzbot]

syzbot has found a reproducer for the following crash on:

HEAD commit:    755d01d17697 Add linux-next specific files for 20190124
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=128f88c4c00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=35842b82e8cde424
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=13e5f517400000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17da1cef400000

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: 0 PID: 7374 Comm: syz-executor189 Not tainted 5.0.0-rc3-next-20190124  
#19
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:ffff88808a6e7698 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: ffff8880930082c0 RCX: 0000000000000000
RDX: 1ffffffff146e05a RSI: 0000000000000004 RDI: ffff88808a6e7600
RBP: ffff88808a6e7748 R08: 1ffff110114dcec0 R09: ffffed10114dcec1
R10: ffffed10114dcec0 R11: 0000000000000003 R12: dffffc0000000000
R13: ffff88808a6e7858 R14: ffff8880930099b8 R15: 0000000000000000
FS:  00007febe4d2d700(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007febe4d2cdb8 CR3: 00000000901a3000 CR4: 00000000001406f0
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
 unshare_nsproxy_namespaces+0xc2/0x200 kernel/nsproxy.c:206
 ksys_unshare+0x6d7/0xfb0 kernel/fork.c:2550
 __do_sys_unshare kernel/fork.c:2618 [inline]
 __se_sys_unshare kernel/fork.c:2616 [inline]
 __x64_sys_unshare+0x31/0x40 kernel/fork.c:2616
 do_syscall_64+0x1a3/0x800 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x449009
Code: e8 6c 14 03 00 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 cb 05 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007febe4d2ccf8 EFLAGS: 00000246 ORIG_RAX: 0000000000000110
RAX: ffffffffffffffda RBX: 00000000006e59f8 RCX: 0000000000449009
RDX: 0000000000449009 RSI: 0000000000449009 RDI: 0000000040000000
RBP: 00000000006e59f0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006e59fc
R13: 00007ffeec84fdaf R14: 00007febe4d2d9c0 R15: 0000000000000001
Modules linked in:
---[ end trace e72b60d04a028cfc ]---
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:ffff88808a6e7698 EFLAGS: 00010246
RAX: dffffc0000000000 RBX: ffff8880930082c0 RCX: 0000000000000000
RDX: 1ffffffff146e05a RSI: 0000000000000004 RDI: ffff88808a6e7600
RBP: ffff88808a6e7748 R08: 1ffff110114dcec0 R09: ffffed10114dcec1
R10: ffffed10114dcec0 R11: 0000000000000003 R12: dffffc0000000000
R13: ffff88808a6e7858 R14: ffff8880930099b8 R15: 0000000000000000
FS:  00007febe4d2d700(0000) GS:ffff8880ae600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007febe4d2cdb8 CR3: 00000000901a3000 CR4: 00000000001406f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400