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authorFlorian Westphal <fw@strlen.de>2017-03-13 16:24:28 +0100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2017-03-22 12:04:17 +0100
commitaed728c38c483650885dfd975dd9f4903e5505bf (patch)
treeb7033890e312c5fb062451c7abe7f1aed155745c /net
parent5f8bc3856e285cc12597879039c17f7397f4b37d (diff)
ipv6: avoid write to a possibly cloned skb
[ Upstream commit 79e49503efe53a8c51d8b695bedc8a346c5e4a87 ] 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@stressinduktion.org> Reported-by: Andreas Karis <akaris@redhat.com> Signed-off-by: Florian Westphal <fw@strlen.de> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'net')
-rw-r--r--net/ipv6/ip6_output.c7
1 files changed, 6 insertions, 1 deletions
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index 58900c21e4e4..8004532fa882 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -742,13 +742,14 @@ 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)
@@ -793,6 +794,10 @@ 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.
*/