[PATCH] ethernet: add sanity check before memory dereferencing

[PATCH] ethernet: add sanity check before memory dereferencing

[Changli Gao]

add sanity check before memory dereferencing

Some callers of eth_type_trans() only can assure the length of the packets
passed to it is not less than ETH_HLEN. We'd better check the packets length
before dereferencing skb->data.

Signed-off-by: Changli Gao <xiaosuo@gmail.com>
----
 net/ethernet/eth.c |    5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)
diff --git a/net/ethernet/eth.c b/net/ethernet/eth.c
index 61ec032..215c839 100644
--- a/net/ethernet/eth.c
+++ b/net/ethernet/eth.c
@@ -158,7 +158,6 @@ EXPORT_SYMBOL(eth_rebuild_header);
 __be16 eth_type_trans(struct sk_buff *skb, struct net_device *dev)
 {
 	struct ethhdr *eth;
-	unsigned char *rawp;
 
 	skb->dev = dev;
 	skb_reset_mac_header(skb);
@@ -199,15 +198,13 @@ __be16 eth_type_trans(struct sk_buff *skb, struct net_device *dev)
 	if (ntohs(eth->h_proto) >= 1536)
 		return eth->h_proto;
 
-	rawp = skb->data;
-
 	/*
 	 *      This is a magic hack to spot IPX packets. Older Novell breaks
 	 *      the protocol design and runs IPX over 802.3 without an 802.2 LLC
 	 *      layer. We look for FFFF which isn't a used 802.2 SSAP/DSAP. This
 	 *      won't work for fault tolerant netware but does for the rest.
 	 */
-	if (*(unsigned short *)rawp == 0xFFFF)
+	if (skb->len >= 2 && *(unsigned short *)(skb->data) == 0xFFFF)
 		return htons(ETH_P_802_3);
 
 	/*

Re: [PATCH] ethernet: add sanity check before memory dereferencing

[David Miller]

From: Changli Gao <xiaosuo@gmail.com>
Date: Tue,  4 May 2010 11:33:48 +0800

> add sanity check before memory dereferencing
> 
> Some callers of eth_type_trans() only can assure the length of the packets
> passed to it is not less than ETH_HLEN. We'd better check the packets length
> before dereferencing skb->data.
> 
> Signed-off-by: Changli Gao <xiaosuo@gmail.com>

We can deference skb->data for at least 16 bytes or so past the end
of the valid packet data area however we want.

It might give garbage values, but it will not cause a fault or any
kind.

We want to remove checks here, not add new ones Changli.