[NETFILTER]: Use pskb_trim in {ip,ip6,nfnetlink}_queue

Based on patch by James D. Nurmi:

I've got some code very dependant on nfnetlink_queue, and turned up a
large number of warns coming from skb_trim.  While it's quite possibly
my code, having not seen it on older kernels made me a bit suspect.

Anyhow, based on some googling I turned up this thread:
http://lkml.org/lkml/2006/8/13/56

And believe the issue to be related, so attached is a small patch to
the kernel -- not sure if this is completely correct, but for anyone
else hitting the WARN_ON(1) in skbuff.h, it might be helpful..

Signed-off-by: James D. Nurmi <jdnurmi@gmail.com>

Ported to ip6_queue and nfnetlink_queue and added return value
checks.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/netfilter/ip_queue.c

@@ -351,9 +351,10 @@ ipq_mangle_ipv4(ipq_verdict_msg_t *v, struct ipq_queue_entry *e)
 	if (v->data_len < sizeof(*user_iph))
 		return 0;
 	diff = v->data_len - e->skb->len;
-	if (diff < 0)
-		skb_trim(e->skb, v->data_len);
-	else if (diff > 0) {
+	if (diff < 0) {
+		if (pskb_trim(e->skb, v->data_len))
+			return -ENOMEM;
+	} else if (diff > 0) {
 		if (v->data_len > 0xFFFF)
 			return -EINVAL;
 		if (diff > skb_tailroom(e->skb)) {

net/ipv6/netfilter/ip6_queue.c

@@ -349,9 +349,10 @@ ipq_mangle_ipv6(ipq_verdict_msg_t *v, struct ipq_queue_entry *e)
 	if (v->data_len < sizeof(*user_iph))
 		return 0;
 	diff = v->data_len - e->skb->len;
-	if (diff < 0)
-		skb_trim(e->skb, v->data_len);
-	else if (diff > 0) {
+	if (diff < 0) {
+		if (pskb_trim(e->skb, v->data_len))
+			return -ENOMEM;
+	} else if (diff > 0) {
 		if (v->data_len > 0xFFFF)
 			return -EINVAL;
 		if (diff > skb_tailroom(e->skb)) {

net/netfilter/nfnetlink_queue.c

@@ -622,9 +622,10 @@ nfqnl_mangle(void *data, int data_len, struct nfqnl_queue_entry *e)
 	int diff;
 
 	diff = data_len - e->skb->len;
-	if (diff < 0)
-		skb_trim(e->skb, data_len);
-	else if (diff > 0) {
+	if (diff < 0) {
+		if (pskb_trim(e->skb, data_len))
+			return -ENOMEM;
+	} else if (diff > 0) {
 		if (data_len > 0xFFFF)
 			return -EINVAL;
 		if (diff > skb_tailroom(e->skb)) {