general protection fault in fib6_purge_rt

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    ee28b30cbbe0 r8169: fix crash if CONFIG_DEBUG_SHIRQ is ena..
git tree:       net
console output: https://syzkaller.appspot.com/x/log.txt?x=10c76ba3400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=c8970c89a0efbb23
dashboard link: https://syzkaller.appspot.com/bug?extid=a25307ad099309f1c2b9
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+a25307ad099309f1c2b9@xxxxxxxxxxxxxxxxxxxxxxxxx

IPv6: ADDRCONF(NETDEV_UP): veth0_to_bridge: link is not ready
device bridge_slave_1 left promiscuous mode
bridge0: port 2(bridge_slave_1) entered disabled state
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: 195 Comm: kworker/u4:3 Not tainted 4.20.0-rc6+ #227
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Workqueue: netns cleanup_net
RIP: 0010:fib6_drop_pcpu_from net/ipv6/ip6_fib.c:920 [inline]
RIP: 0010:fib6_purge_rt+0x5ce/0x7e0 net/ipv6/ip6_fib.c:956
Code: 0f b6 35 99 f1 33 03 31 ff 44 89 f6 e8 bb b7 a0 fa 45 84 f6 0f 84 ec  
00 00 00 e8 dd b6 a0 fa 49 8d 47 70 48 89 c2 48 c1 ea 03 <42> 80 3c 22 00  
0f 85 b5 01 00 00 48 8b 8d e0 fe ff ff 48 89 c2 48
RSP: 0018:ffff8881d8cadf18 EFLAGS: 00010202
RAX: 0000000000003400 RBX: 0000000000000001 RCX: ffffffff86decea0
RDX: 0000000000000680 RSI: ffffffff86decd93 RDI: 0000000000000005
RBP: ffff8881d8cae048 R08: ffff8881d8ca05c0 R09: ffffed1036ea6e1d
R10: ffffed1036ea6e1d R11: ffff8881b75370ef R12: dffffc0000000000
R13: ffff8881b75370c0 R14: 0000000000000001 R15: 0000000000003390
FS:  0000000000000000(0000) GS:ffff8881daf00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000619570 CR3: 00000001c28ac000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 fib6_del_route net/ipv6/ip6_fib.c:1809 [inline]
 fib6_del+0xbe0/0x12e0 net/ipv6/ip6_fib.c:1840
 fib6_clean_node+0x44c/0x650 net/ipv6/ip6_fib.c:2002
 fib6_walk_continue+0x4b1/0x8e0 net/ipv6/ip6_fib.c:1924
 fib6_walk+0x95/0xf0 net/ipv6/ip6_fib.c:1972
 fib6_clean_tree+0x21c/0x420 net/ipv6/ip6_fib.c:2051
 __fib6_clean_all+0x235/0x440 net/ipv6/ip6_fib.c:2067
 fib6_clean_all+0x2a/0x40 net/ipv6/ip6_fib.c:2078
 rt6_sync_down_dev+0x17a/0x1b0 net/ipv6/route.c:4038
 rt6_disable_ip+0x87/0x720 net/ipv6/route.c:4043
 addrconf_ifdown+0x168/0x1650 net/ipv6/addrconf.c:3669
 addrconf_notify+0x6de/0x2770 net/ipv6/addrconf.c:3594
 notifier_call_chain+0x17e/0x380 kernel/notifier.c:93
 __raw_notifier_call_chain kernel/notifier.c:394 [inline]
 raw_notifier_call_chain+0x2d/0x40 kernel/notifier.c:401
 call_netdevice_notifiers_info+0x3f/0x90 net/core/dev.c:1733
 call_netdevice_notifiers net/core/dev.c:1751 [inline]
 dev_close_many+0x40e/0x860 net/core/dev.c:1503
 rollback_registered_many+0x543/0x1250 net/core/dev.c:7991
 unregister_netdevice_many+0xfa/0x4c0 net/core/dev.c:9119
 default_device_exit_batch+0x43a/0x540 net/core/dev.c:9588
 ops_exit_list.isra.5+0x105/0x160 net/core/net_namespace.c:156
 cleanup_net+0x555/0xb10 net/core/net_namespace.c:551
 process_one_work+0xc90/0x1c40 kernel/workqueue.c:2153
 worker_thread+0x17f/0x1390 kernel/workqueue.c:2296
 kthread+0x35a/0x440 kernel/kthread.c:246
 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:352
Modules linked in:
---[ end trace 42ffb82098483a68 ]---
RIP: 0010:fib6_drop_pcpu_from net/ipv6/ip6_fib.c:920 [inline]
RIP: 0010:fib6_purge_rt+0x5ce/0x7e0 net/ipv6/ip6_fib.c:956
Code: 0f b6 35 99 f1 33 03 31 ff 44 89 f6 e8 bb b7 a0 fa 45 84 f6 0f 84 ec  
00 00 00 e8 dd b6 a0 fa 49 8d 47 70 48 89 c2 48 c1 ea 03 <42> 80 3c 22 00  
0f 85 b5 01 00 00 48 8b 8d e0 fe ff ff 48 89 c2 48
RSP: 0018:ffff8881d8cadf18 EFLAGS: 00010202
RAX: 0000000000003400 RBX: 0000000000000001 RCX: ffffffff86decea0
RDX: 0000000000000680 RSI: ffffffff86decd93 RDI: 0000000000000005
RBP: ffff8881d8cae048 R08: ffff8881d8ca05c0 R09: ffffed1036ea6e1d
R10: ffffed1036ea6e1d R11: ffff8881b75370ef R12: dffffc0000000000
R13: ffff8881b75370c0 R14: 0000000000000001 R15: 0000000000003390
FS:  0000000000000000(0000) GS:ffff8881daf00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000619570 CR3: 00000001c28ac000 CR4: 00000000001406e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


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