[IPX]: Another nonlinear receive fix

Need to check some more cases in IPX receive.  If the skb is purely
fragments, the IPX header needs to be extracted. The function
pskb_may_pull() may in theory invalidate all the pointers in the skb,
so references to ipx header must be refreshed.
Signed-off-by: NStephen Hemminger <shemminger@osdl.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipx/af_ipx.c

@@ -1642,14 +1642,17 @@ static int ipx_rcv(struct sk_buff *skb, struct net_device *dev, struct packet_ty
 	if ((skb = skb_share_check(skb, GFP_ATOMIC)) == NULL)
 		goto out;
 
-	ipx		= ipx_hdr(skb);
-	ipx_pktsize	= ntohs(ipx->ipx_pktsize);
+	if (!pskb_may_pull(skb, sizeof(struct ipxhdr)))
+		goto drop;
+
+	ipx_pktsize = ntohs(ipxhdr(skb)->ipx_pktsize);
 	
 	/* Too small or invalid header? */
 	if (ipx_pktsize < sizeof(struct ipxhdr) ||
 	    !pskb_may_pull(skb, ipx_pktsize))
 		goto drop;
                         
+	ipx = ipx_hdr(skb);
 	if (ipx->ipx_checksum != IPX_NO_CHECKSUM &&
 	   ipx->ipx_checksum != ipx_cksum(ipx, ipx_pktsize))
 		goto drop;