From 79e49503efe53a8c51d8b695bedc8a346c5e4a87 Mon Sep 17 00:00:00 2001 From: Florian Westphal Date: Mon, 13 Mar 2017 16:24:28 +0100 Subject: ipv6: avoid write to a possibly cloned skb 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 Reported-by: Andreas Karis Signed-off-by: Florian Westphal Signed-off-by: David S. Miller --- net/ipv6/ip6_output.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) (limited to 'net/ipv6/ip6_output.c') diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c index df42096e1f04..58f6288e9ba5 100644 --- a/net/ipv6/ip6_output.c +++ b/net/ipv6/ip6_output.c @@ -768,13 +768,14 @@ slow_path: * Fragment the datagram. */ - *prevhdr = NEXTHDR_FRAGMENT; troom = rt->dst.dev->needed_tailroom; /* * Keep copying data until we run out. */ while (left > 0) { + u8 *fragnexthdr_offset; + len = left; /* IF: it doesn't fit, use 'mtu' - the data space left */ if (len > mtu) @@ -819,6 +820,10 @@ slow_path: */ skb_copy_from_linear_data(skb, skb_network_header(frag), hlen); + fragnexthdr_offset = skb_network_header(frag); + fragnexthdr_offset += prevhdr - skb_network_header(skb); + *fragnexthdr_offset = NEXTHDR_FRAGMENT; + /* * Build fragment header. */ -- cgit