===== drivers/net/pppoe.c 1.48 vs edited =====
--- 1.48/drivers/net/pppoe.c	2005-01-21 16:02:12 +11:00
+++ edited/drivers/net/pppoe.c	2005-03-01 11:20:44 +11:00
@@ -338,7 +338,9 @@
 		struct pppoe_hdr *ph = (struct pppoe_hdr *) skb->nh.raw;
 		int len = ntohs(ph->length);
 		skb_pull(skb, sizeof(struct pppoe_hdr));
-		skb_trim(skb, len);
+		skb_postpull_rcsum(skb, ph, sizeof(*ph));
+		if (pskb_trim_rcsum(skb, len))
+			goto abort_kfree;
 
 		ppp_input(&po->chan, skb);
 	} else if (sk->sk_state & PPPOX_RELAY) {
===== include/linux/skbuff.h 1.60 vs edited =====
--- 1.60/include/linux/skbuff.h	2005-02-06 14:23:06 +11:00
+++ edited/include/linux/skbuff.h	2005-03-01 11:15:43 +11:00
@@ -1054,6 +1054,42 @@
 	return __skb_linearize(skb, gfp);
 }
 
+/**
+ *	skb_postpull_rcsum - update checksum for received skb after pull
+ *	@skb: buffer to update
+ *	@start: start of data before pull
+ *	@len: length of data pulled
+ *
+ *	After doing a pull on a received packet, you need to call this to
+ *	update the CHECKSUM_HW checksum, or set ip_summed to CHECKSUM_NONE
+ *	so that it can be recomputed from scratch.
+ */
+
+static inline void skb_postpull_rcsum(struct sk_buff *skb,
+					 const void *start, int len)
+{
+	if (skb->ip_summed == CHECKSUM_HW)
+		skb->csum = csum_sub(skb->csum, csum_partial(start, len, 0));
+}
+
+/**
+ *	pskb_trim_rcsum - trim received skb and update checksum
+ *	@skb: buffer to trim
+ *	@len: new length
+ *
+ *	This is exactly the same as pskb_trim except that it ensures the
+ *	checksum of received packets are still valid after the operation.
+ */
+
+static inline int pskb_trim_rcsum(struct sk_buff *skb, unsigned int len)
+{
+	if (len >= skb->len)
+		return 0;
+	if (skb->ip_summed == CHECKSUM_HW)
+		skb->ip_summed = CHECKSUM_NONE;
+	return __pskb_trim(skb, len);
+}
+
 static inline void *kmap_skb_frag(const skb_frag_t *frag)
 {
 #ifdef CONFIG_HIGHMEM
===== net/ipv4/ip_gre.c 1.46 vs edited =====
--- 1.46/net/ipv4/ip_gre.c	2005-01-14 15:41:05 +11:00
+++ edited/net/ipv4/ip_gre.c	2005-03-01 11:17:35 +11:00
@@ -618,10 +618,8 @@
 
 		skb->mac.raw = skb->nh.raw;
 		skb->nh.raw = __pskb_pull(skb, offset);
+		skb_postpull_rcsum(skb, skb->mac.raw, offset);
 		memset(&(IPCB(skb)->opt), 0, sizeof(struct ip_options));
-		if (skb->ip_summed == CHECKSUM_HW)
-			skb->csum = csum_sub(skb->csum,
-					     csum_partial(skb->mac.raw, skb->nh.raw-skb->mac.raw, 0));
 		skb->pkt_type = PACKET_HOST;
 #ifdef CONFIG_NET_IPGRE_BROADCAST
 		if (MULTICAST(iph->daddr)) {
===== net/ipv4/ip_input.c 1.27 vs edited =====
--- 1.27/net/ipv4/ip_input.c	2005-01-27 17:03:17 +11:00
+++ edited/net/ipv4/ip_input.c	2005-03-01 11:21:19 +11:00
@@ -410,10 +410,9 @@
 		 * is IP we can trim to the true length of the frame.
 		 * Note this now means skb->len holds ntohs(iph->tot_len).
 		 */
-		if (skb->len > len) {
-			__pskb_trim(skb, len);
-			if (skb->ip_summed == CHECKSUM_HW)
-				skb->ip_summed = CHECKSUM_NONE;
+		if (pskb_trim_rcsum(skb, len)) {
+			IP_INC_STATS_BH(IPSTATS_MIB_INDISCARDS);
+			goto drop;
 		}
 	}
 
===== net/ipv6/ip6_input.c 1.22 vs edited =====
--- 1.22/net/ipv6/ip6_input.c	2004-08-23 18:15:14 +10:00
+++ edited/net/ipv6/ip6_input.c	2005-03-01 11:24:32 +11:00
@@ -95,15 +95,11 @@
 	if (pkt_len || hdr->nexthdr != NEXTHDR_HOP) {
 		if (pkt_len + sizeof(struct ipv6hdr) > skb->len)
 			goto truncated;
-		if (pkt_len + sizeof(struct ipv6hdr) < skb->len) {
-			if (__pskb_trim(skb, pkt_len + sizeof(struct ipv6hdr))){
-				IP6_INC_STATS_BH(IPSTATS_MIB_INHDRERRORS);
-				goto drop;
-			}
-			hdr = skb->nh.ipv6h;
-			if (skb->ip_summed == CHECKSUM_HW)
-				skb->ip_summed = CHECKSUM_NONE;
+		if (pskb_trim_rcsum(skb, pkt_len + sizeof(struct ipv6hdr))) {
+			IP6_INC_STATS_BH(IPSTATS_MIB_INHDRERRORS);
+			goto drop;
 		}
+		hdr = skb->nh.ipv6h;
 	}
 
 	if (hdr->nexthdr == NEXTHDR_HOP) {
@@ -138,7 +134,6 @@
 	unsigned int nhoff;
 	int nexthdr;
 	u8 hash;
-	int cksum_sub = 0;
 
 	skb->h.raw = skb->nh.raw + sizeof(struct ipv6hdr);
 
@@ -173,11 +168,8 @@
 		if (ipprot->flags & INET6_PROTO_FINAL) {
 			struct ipv6hdr *hdr;	
 
-			if (!cksum_sub && skb->ip_summed == CHECKSUM_HW) {
-				skb->csum = csum_sub(skb->csum,
-						     csum_partial(skb->nh.raw, skb->h.raw-skb->nh.raw, 0));
-				cksum_sub++;
-			}
+			skb_postpull_rcsum(skb, skb->nh.raw,
+					   skb->h.raw - skb->nh.raw);
 			hdr = skb->nh.ipv6h;
 			if (ipv6_addr_is_multicast(&hdr->daddr) &&
 			    !ipv6_chk_mcast_addr(skb->dev, &hdr->daddr,