netdev - Re: GRO/GSO hiding PMTU?

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20110210.150759.59671055.davem@davemloft.net>
Date:	Thu, 10 Feb 2011 15:07:59 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	herbert@...dor.apana.org.au
Cc:	netdev@...r.kernel.org, netfilter-devel@...r.kernel.org
Subject: Re: GRO/GSO hiding PMTU?

From: David Miller <davem@...emloft.net>
Date: Thu, 10 Feb 2011 14:55:55 -0800 (PST)

> I suspect that the packet arrives on eth1, accumulates into GRO, and
> thus marked as GSO as well, then GSO/TSO on output to eth0 is
> re-segmenting things transparently, and we're not getting the ICMP
> frag-needed message and the packet drop because of the skb_is_gso()
> check in ip_forward().
> 
> 	if (unlikely(skb->len > dst_mtu(&rt->dst) && !skb_is_gso(skb) &&
> 		     (ip_hdr(skb)->frag_off & htons(IP_DF))) && !skb->local_df) {
> 		IP_INC_STATS(dev_net(rt->dst.dev), IPSTATS_MIB_FRAGFAILS);
> 		icmp_send(skb, ICMP_DEST_UNREACH, ICMP_FRAG_NEEDED,
> 			  htonl(dst_mtu(&rt->dst)));
> 		goto drop;
> 	}
> 
> So if that's what is happening, that's cute, but I think we need to
> fix this :-)
> 
> Perhaps the check in ip_forward() should instead validate the gso_size
> in the skb_is_gso() case?
> 
> That'd be a little tricky since gso_size is an MSS value whereas what
> we're checking against (skb->len) is the full packet size, headers and
> all.

Nevermind, I turned off gso/tso on eth0 (outgoing interface) and it still
happens.

I guess netfilter or something else is causing this.

--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html