leandrof/linux
1
0
Fork 0
forked from Minki/linux
Code Issues Pull Requests Packages Projects Releases Wiki Activity

ipv6: avoid write to a possibly cloned skb

Browse Source 
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>
This commit is contained in:
Florian Westphal 2017-03-13 16:24:28 +01:00 committed by David S. Miller
parent 6e526fdff7
commit 79e49503ef
1 changed files with 6 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
net/ipv6/ip6_output.c
View File

@ -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.
*/