ipv6: Add lwtunnel encap size of all siblings in nexthop calculation

In the Linux kernel, the following vulnerability has been resolved:

ipv6: Add lwtunnel encap size of all siblings in nexthop calculation

In function rt6_nlmsg_size(), the length of nexthop is calculated

by multipling the nexthop length of fib6_info and the number of

siblings. However if the fib6_info has no lwtunnel but the siblings

have lwtunnels, the nexthop length is less than it should be, and

it will trigger a warning in inet6_rt_notify() as follows:

WARNING: CPU: 0 PID: 6082 at net/ipv6/route.c:6180 inet6_rt_notify+0x120/0x130

......

Call Trace:

<TASK>

fib6_add_rt2node+0x685/0xa30

fib6_add+0x96/0x1b0

ip6_route_add+0x50/0xd0

inet6_rtm_newroute+0x97/0xa0

rtnetlink_rcv_msg+0x156/0x3d0

netlink_rcv_skb+0x5a/0x110

netlink_unicast+0x246/0x350

netlink_sendmsg+0x250/0x4c0

sock_sendmsg+0x66/0x70

___sys_sendmsg+0x7c/0xd0

__sys_sendmsg+0x5d/0xb0

do_syscall_64+0x3f/0x90

entry_SYSCALL_64_after_hwframe+0x72/0xdc

This bug can be reproduced by script:

ip -6 addr add 2002::2/64 dev ens2

ip -6 route add 100::/64 via 2002::1 dev ens2 metric 100

for i in 10 20 30 40 50 60 70;

do

ip link add link ens2 name ipv_$i type ipvlan

ip -6 addr add 2002::$i/64 dev ipv_$i

ifconfig ipv_$i up

done

for i in 10 20 30 40 50 60;

do

ip -6 route append 100::/64 encap ip6 dst 2002::$i via 2002::1

dev ipv_$i metric 100

done

ip -6 route append 100::/64 via 2002::1 dev ipv_70 metric 100

This patch fixes it by adding nexthop_len of every siblings using

rt6_nh_nlmsg_size().