From: Hangbin Liu <liuhang...@gmail.com>
Date: Thu, 22 Aug 2019 22:19:47 +0800
> When we send a packet larger than PMTU, we need to reply with
> icmp_send(ICMP_FRAG_NEEDED) or icmpv6_send(ICMPV6_PKT_TOOBIG).
>
> But with collect_md mode, kernel will crash while accessing the dst dev
> as __metadata_dst_init() init dst->dev to NULL by default. Here is what
> the code path looks like, for GRE:
...
> We could not fix it in __metadata_dst_init() as there is no dev supplied.
> Look in to the __icmp_send()/decode_session{4,6} code we could find the dst
> dev is actually not needed. In __icmp_send(), we could get the net by
> skb->dev.
> For decode_session{4,6}, as it was called by xfrm_decode_session_reverse()
> in this scenario, the oif is not used by
> fl4->flowi4_oif = reverse ? skb->skb_iif : oif;
>
> The reproducer is easy:
...
Series applied, and queued up for -stable, thanks!
