WARNING in fib6_add (2)

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    528bff0cdb66 tools: bpftool: fix a bitfield pretty print i..
git tree:       bpf
console output: https://syzkaller.appspot.com/x/log.txt?x=12f29a93400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=73e2bc0cb6463446
dashboard link: https://syzkaller.appspot.com/bug?extid=60cc5bc1296c8afcf739
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+60cc5bc1296c8afcf739@xxxxxxxxxxxxxxxxxxxxxxxxx

IPv6: Can't replace route, no match found
netlink: 7 bytes leftover after parsing attributes in process  
`syz-executor1'.
IPv6: NLM_F_REPLACE set, but no existing node found!
WARNING: CPU: 1 PID: 28238 at net/ipv6/ip6_fib.c:1360  
fib6_add+0x1106/0x14c0 net/ipv6/ip6_fib.c:1360
Kernel panic - not syncing: panic_on_warn set ...
CPU: 1 PID: 28238 Comm: syz-executor5 Not tainted 4.20.0-rc3+ #92
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x244/0x39d lib/dump_stack.c:113
 panic+0x2ad/0x55c kernel/panic.c:188
 __warn.cold.8+0x20/0x45 kernel/panic.c:540
 report_bug+0x254/0x2d0 lib/bug.c:186
 fixup_bug arch/x86/kernel/traps.c:178 [inline]
 do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:271
 do_invalid_op+0x36/0x40 arch/x86/kernel/traps.c:290
 invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:969
RIP: 0010:fib6_add+0x1106/0x14c0 net/ipv6/ip6_fib.c:1360
Code: 08 49 8d bf a8 0c 00 00 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 8d 03  
00 00 4d 8b bf a8 0c 00 00 e9 15 fd ff ff e8 6a aa 9f fa <0f> 0b 48 8b 95  
f0 fc ff ff 48 b8 00 00 00 00 00 fc ff df 48 c1 ea
RSP: 0018:ffff8881d22cee40 EFLAGS: 00010216
RAX: 0000000000040000 RBX: ffff8881d22cf590 RCX: ffffc90011a88000
RDX: 0000000000008f15 RSI: ffffffff86dfe086 RDI: ffff888189100920
RBP: ffff8881d22cf198 R08: ffff8881d8398580 R09: ffffed103a477e5d
R10: ffffed103a477e5d R11: ffff8881d23bf2ef R12: 00000000fffffffe
R13: ffff888189100900 R14: ffff8881b3c54080 R15: 0000000000000000
 __ip6_ins_rt+0x54/0x80 net/ipv6/route.c:1155
 ip6_route_multipath_add+0x94f/0x18b0 net/ipv6/route.c:4391
 inet6_rtm_newroute+0xe3/0x160 net/ipv6/route.c:4521
 rtnetlink_rcv_msg+0x46a/0xc20 net/core/rtnetlink.c:4947
kobject: 'loop3' (000000001b475654): kobject_uevent_env
 netlink_rcv_skb+0x172/0x440 net/netlink/af_netlink.c:2477
 rtnetlink_rcv+0x1c/0x20 net/core/rtnetlink.c:4965
kobject: 'loop3' (000000001b475654): fill_kobj_path: path  
= '/devices/virtual/block/loop3'
 netlink_unicast_kernel net/netlink/af_netlink.c:1310 [inline]
 netlink_unicast+0x5a5/0x760 net/netlink/af_netlink.c:1336
 netlink_sendmsg+0xa18/0xfc0 net/netlink/af_netlink.c:1917
kobject: 'loop2' (000000002cda1b69): kobject_uevent_env
kobject: 'loop2' (000000002cda1b69): fill_kobj_path: path  
= '/devices/virtual/block/loop2'
 sock_sendmsg_nosec net/socket.c:621 [inline]
 sock_sendmsg+0xd5/0x120 net/socket.c:631
 ___sys_sendmsg+0x7fd/0x930 net/socket.c:2116
 __sys_sendmsg+0x11d/0x280 net/socket.c:2154
 __do_sys_sendmsg net/socket.c:2163 [inline]
 __se_sys_sendmsg net/socket.c:2161 [inline]
 __x64_sys_sendmsg+0x78/0xb0 net/socket.c:2161
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x457569
Code: fd b3 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 cb b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f9f096ccc78 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000457569
RDX: 0000000000000000 RSI: 0000000020000080 RDI: 0000000000000003
RBP: 000000000072bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f9f096cd6d4
R13: 00000000004c3f7d R14: 00000000004d6778 R15: 00000000ffffffff
Kernel Offset: disabled
Rebooting in 86400 seconds..


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