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Date: Mon, 13 Mar 2017 12:54:01 -0700 (PDT) From: David Miller <davem@...emloft.net> To: fw@...len.de Cc: netdev@...r.kernel.org, hannes@...essinduktion.org Subject: Re: [PATCH nf] ipv6: avoid write to a possibly cloned skb From: Florian Westphal <fw@...len.de> Date: Mon, 13 Mar 2017 16:24:28 +0100 > ip6_fragment, in case skb has a fraglist, checks if the > skb is cloned. If it is, it will move to the 'slow path' and allocates > new skbs for each fragment. > > However, right before entering the slowpath loop, it updates the > nexthdr value of the last ipv6 extension header to NEXTHDR_FRAGMENT, > to account for the fragment header that will be inserted in the new > ipv6-fragment skbs. > > In case original skb is cloned this munges nexthdr value of another > skb. Avoid this by doing the nexthdr update for each of the new fragment > skbs separately. > > This was observed with tcpdump on a bridge device where netfilter ipv6 > reassembly is active: tcpdump shows malformed fragment headers as > the l4 header (icmpv6, tcp, etc). is decoded as a fragment header. > > Cc: Hannes Frederic Sowa <hannes@...essinduktion.org> > Reported-by: Andreas Karis <akaris@...hat.com> > Signed-off-by: Florian Westphal <fw@...len.de> Great catch Florian, applied, thanks.
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