On Tue, Oct 23, 2018 at 7:47 AM, Florian Westphal <fw@xxxxxxxxx> wrote:
> Unlike ipv4 and normal ipv6 defrag, netfilter ipv6 defragmentation did
> not save/restore skb->dst.
>
> This causes oops when handling locally generated ipv6 fragments, as
> output path needs a valid dst.
>
> Reported-by: Maciej Żenczykowski <zenczykowski@xxxxxxxxx>
> Fixes: 84379c9afe01 ("netfilter: ipv6: nf_defrag: drop skb dst before queueing")
> Signed-off-by: Florian Westphal <fw@xxxxxxxxx>
> ---
> net/ipv6/netfilter/nf_conntrack_reasm.c | 13 +++++++++----
> 1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/net/ipv6/netfilter/nf_conntrack_reasm.c b/net/ipv6/netfilter/nf_conntrack_reasm.c
> index 8f68a518d9db..f76bd4d15704 100644
> --- a/net/ipv6/netfilter/nf_conntrack_reasm.c
> +++ b/net/ipv6/netfilter/nf_conntrack_reasm.c
> @@ -587,11 +587,16 @@ int nf_ct_frag6_gather(struct net *net, struct sk_buff *skb, u32 user)
> */
> ret = -EINPROGRESS;
> if (fq->q.flags == (INET_FRAG_FIRST_IN | INET_FRAG_LAST_IN) &&
> - fq->q.meat == fq->q.len &&
> - nf_ct_frag6_reasm(fq, skb, dev))
> - ret = 0;
> - else
> + fq->q.meat == fq->q.len) {
> + unsigned long orefdst = skb->_skb_refdst;
> +
> + skb->_skb_refdst = 0UL;
> + if (nf_ct_frag6_reasm(fq, skb, dev))
> + ret = 0;
> + skb->_skb_refdst = orefdst;
> + } else {
> skb_dst_drop(skb);
> + }
>
> out_unlock:
> spin_unlock_bh(&fq->q.lock);
> --
> 2.18.1
>
I don't quite follow how this fixes things, but I'll trust you on it.
(nor do I understand why only 4.9 LTS appears to crash with a null ptr deref)
Thanks for the fix.
