[lucid/fsl-imx51, maverick, maverick/ti-omap4, natty, natty/ti-omap4 CVE 1/1] gro: Only reset frag0 when skb can be pulled

[Andy Whitcroft]

From: Herbert Xu <herbert at gondor.apana.org.au>

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 at gondor.apana.org.au>
Signed-off-by: David S. Miller <davem at davemloft.net>

(cherry picked from commit 17dd759c67f21e34f2156abcf415e1f60605a188)
CVE-2011-2723
BugLink: http://bugs.launchpad.net/bugs/844371
Signed-off-by: Andy Whitcroft <apw at canonical.com>
---
 include/linux/netdevice.h |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index d4a4d98..b337b81 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1152,9 +1152,12 @@ 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)
-- 
1.7.4.1