Re: net/icmp: null-ptr-deref in icmp6_send

On Tue, Nov 22, 2016 at 2:23 AM, Andrey Konovalov [off-list ref] wrote:

Hi,

I've got the following error report while fuzzing the kernel with syzkaller.

It seems that skb_dst(skb) may end up being NULL.

As far as I can see the bug was introduced in commit 5d41ce29e ("net:
icmp6_send should use dst dev to determine L3 domain").
ICMP v4 probaly has similar issue due to 9d1a6c4ea ("net:
icmp_route_lookup should use rt dev to determine L3 domain").

ipv6_parse_hopopts() is called before NF_INET_PRE_ROUTING,
so the skb_dst could be NULL.

I have no idea what commit 5d41ce29e tried to fix, but we already
use skb->dev a few lines before l3mdev_master_ifindex(), so I don't
understand why skb->dev could be NULL, maybe just for vrf dev?