gro: Only reset frag0 when skb can be pulled, CVE-2011-2723

Currently skb_gro_header_slow unconditionally resets frag0 and
frag0_len.  However, when we can't pull on the skb this leaves
the GRO fields in an inconsistent state.

This patch fixes this by only resetting those fields after the
pskb_may_pull test.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

(cherry picked from commit 17dd759c67f21e34f2156abcf415e1f60605a188)
CVE-2011-2723
BugLink: http://bugs.launchpad.net/bugs/844371
Signed-off-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 71caf7a..191e4aa 100644 (file)
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1433,9 +1433,12 @@ static inline int skb_gro_header_hard(struct sk_buff *skb, unsigned int hlen)
 static inline void *skb_gro_header_slow(struct sk_buff *skb, unsigned int hlen,
                                        unsigned int offset)
 {
+       if (!pskb_may_pull(skb, hlen))
+               return NULL;
+
        NAPI_GRO_CB(skb)->frag0 = NULL;
        NAPI_GRO_CB(skb)->frag0_len = 0;
-       return pskb_may_pull(skb, hlen) ? skb->data + offset : NULL;
+       return skb->data + offset;
 }
 
 static inline void *skb_gro_mac_header(struct sk_buff *skb)