[NETFILTER]: {ip,ip6,nfnetlink}_queue: fix SKB_LINEAR_ASSERT when mangling packet data

As reported by Tomas Simonaitis <tomas.simonaitis@gmail.com>,
inserting new data in skbs queued over {ip,ip6,nfnetlink}_queue
triggers a SKB_LINEAR_ASSERT in skb_put().

Going back through the git history, it seems this bug is present since
at least 2.6.12-rc2, probably even since the removal of
skb_linearize() for netfilter.

Linearize non-linear skbs through skb_copy_expand() when enlarging
them.  Tested by Thomas, fixes bugzilla #9933.
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/netfilter/ip_queue.c

@@ -283,8 +283,8 @@ static int
 ipq_mangle_ipv4(ipq_verdict_msg_t *v, struct nf_queue_entry *e)
 {
 	int diff;
-	int err;
 	struct iphdr *user_iph = (struct iphdr *)v->payload;
+	struct sk_buff *nskb;
 
 	if (v->data_len < sizeof(*user_iph))
 		return 0;
@@ -296,14 +296,16 @@ ipq_mangle_ipv4(ipq_verdict_msg_t *v, struct nf_queue_entry *e)
 		if (v->data_len > 0xFFFF)
 			return -EINVAL;
 		if (diff > skb_tailroom(e->skb)) {
-			err = pskb_expand_head(e->skb, 0,
+			nskb = skb_copy_expand(e->skb, 0,
 					       diff - skb_tailroom(e->skb),
 					       GFP_ATOMIC);
-			if (err) {
+			if (!nskb) {
 				printk(KERN_WARNING "ip_queue: error "
-				      "in mangle, dropping packet: %d\n", -err);
-				return err;
+				      "in mangle, dropping packet\n");
+				return -ENOMEM;
 			}
+			kfree_skb(e->skb);
+			e->skb = nskb;
 		}
 		skb_put(e->skb, diff);
 	}

net/ipv6/netfilter/ip6_queue.c

@@ -285,8 +285,8 @@ static int
 ipq_mangle_ipv6(ipq_verdict_msg_t *v, struct nf_queue_entry *e)
 {
 	int diff;
-	int err;
 	struct ipv6hdr *user_iph = (struct ipv6hdr *)v->payload;
+	struct sk_buff *nskb;
 
 	if (v->data_len < sizeof(*user_iph))
 		return 0;
@@ -298,14 +298,16 @@ ipq_mangle_ipv6(ipq_verdict_msg_t *v, struct nf_queue_entry *e)
 		if (v->data_len > 0xFFFF)
 			return -EINVAL;
 		if (diff > skb_tailroom(e->skb)) {
-			err = pskb_expand_head(e->skb, 0,
+			nskb = skb_copy_expand(e->skb, 0,
 					       diff - skb_tailroom(e->skb),
 					       GFP_ATOMIC);
-			if (err) {
+			if (!nskb) {
 				printk(KERN_WARNING "ip6_queue: OOM "
 				      "in mangle, dropping packet\n");
-				return err;
+				return -ENOMEM;
 			}
+			kfree_skb(e->skb);
+			e->skb = nskb;
 		}
 		skb_put(e->skb, diff);
 	}

net/netfilter/nfnetlink_queue.c

@@ -443,8 +443,8 @@ err_out:
 static int
 nfqnl_mangle(void *data, int data_len, struct nf_queue_entry *e)
 {
+	struct sk_buff *nskb;
 	int diff;
-	int err;
 
 	diff = data_len - e->skb->len;
 	if (diff < 0) {
@@ -454,14 +454,16 @@ nfqnl_mangle(void *data, int data_len, struct nf_queue_entry *e)
 		if (data_len > 0xFFFF)
 			return -EINVAL;
 		if (diff > skb_tailroom(e->skb)) {
-			err = pskb_expand_head(e->skb, 0,
+			nskb = skb_copy_expand(e->skb, 0,
 					       diff - skb_tailroom(e->skb),
 					       GFP_ATOMIC);
-			if (err) {
+			if (!nskb) {
 				printk(KERN_WARNING "nf_queue: OOM "
 				      "in mangle, dropping packet\n");
-				return err;
+				return -ENOMEM;
 			}
+			kfree_skb(e->skb);
+			e->skb = nskb;
 		}
 		skb_put(e->skb, diff);
 	}