[NETFILTER]: Do not copy skb in skb_make_writable

Now that all callers of netfilter can guarantee that the skb is not shared,
we no longer have to copy the skb in skb_make_writable.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

4 files changed, 18 insertions, 28 deletions

diff --git a/net/netfilter/core.c b/net/netfilter/core.c
index a523fa4136e..2c9e8e3652d 100644
--- a/net/netfilter/core.c
+++ b/net/netfilter/core.c
@@ -196,34 +196,24 @@ unlock:
 EXPORT_SYMBOL(nf_hook_slow);
 
 
-int skb_make_writable(struct sk_buff **pskb, unsigned int writable_len)
+int skb_make_writable(struct sk_buff *skb, unsigned int writable_len)
 {
-	struct sk_buff *nskb;
-
-	if (writable_len > (*pskb)->len)
+	if (writable_len > skb->len)
 		return 0;
 
 	/* Not exclusive use of packet?  Must copy. */
-	if (skb_cloned(*pskb) && !skb_clone_writable(*pskb, writable_len))
-		goto copy_skb;
-	if (skb_shared(*pskb))
-		goto copy_skb;
-
-	return pskb_may_pull(*pskb, writable_len);
-
-copy_skb:
-	nskb = skb_copy(*pskb, GFP_ATOMIC);
-	if (!nskb)
-		return 0;
-	BUG_ON(skb_is_nonlinear(nskb));
-
-	/* Rest of kernel will get very unhappy if we pass it a
-	   suddenly-orphaned skbuff */
-	if ((*pskb)->sk)
-		skb_set_owner_w(nskb, (*pskb)->sk);
-	kfree_skb(*pskb);
-	*pskb = nskb;
-	return 1;
+	if (!skb_cloned(skb)) {
+		if (writable_len <= skb_headlen(skb))
+			return 1;
+	} else if (skb_clone_writable(skb, writable_len))
+		return 1;
+
+	if (writable_len <= skb_headlen(skb))
+		writable_len = 0;
+	else
+		writable_len -= skb_headlen(skb);
+
+	return !!__pskb_pull_tail(skb, writable_len);
 }
 EXPORT_SYMBOL(skb_make_writable);
 
diff --git a/net/netfilter/nfnetlink_queue.c b/net/netfilter/nfnetlink_queue.c
index 49f0480afe0..6ba98acdd7a 100644
--- a/net/netfilter/nfnetlink_queue.c
+++ b/net/netfilter/nfnetlink_queue.c
@@ -644,7 +644,7 @@ nfqnl_mangle(void *data, int data_len, struct nfqnl_queue_entry *e)
 		}
 		skb_put(e->skb, diff);
 	}
-	if (!skb_make_writable(&e->skb, data_len))
+	if (!skb_make_writable(e->skb, data_len))
 		return -ENOMEM;
 	skb_copy_to_linear_data(e->skb, data, data_len);
 	e->skb->ip_summed = CHECKSUM_NONE;
diff --git a/net/netfilter/xt_DSCP.c b/net/netfilter/xt_DSCP.c
index 798ab731009..17066167438 100644
--- a/net/netfilter/xt_DSCP.c
+++ b/net/netfilter/xt_DSCP.c
@@ -36,7 +36,7 @@ static unsigned int target(struct sk_buff **pskb,
 	u_int8_t dscp = ipv4_get_dsfield(ip_hdr(*pskb)) >> XT_DSCP_SHIFT;
 
 	if (dscp != dinfo->dscp) {
-		if (!skb_make_writable(pskb, sizeof(struct iphdr)))
+		if (!skb_make_writable(*pskb, sizeof(struct iphdr)))
 			return NF_DROP;
 
 		ipv4_change_dsfield(ip_hdr(*pskb), (__u8)(~XT_DSCP_MASK),
@@ -57,7 +57,7 @@ static unsigned int target6(struct sk_buff **pskb,
 	u_int8_t dscp = ipv6_get_dsfield(ipv6_hdr(*pskb)) >> XT_DSCP_SHIFT;
 
 	if (dscp != dinfo->dscp) {
-		if (!skb_make_writable(pskb, sizeof(struct ipv6hdr)))
+		if (!skb_make_writable(*pskb, sizeof(struct ipv6hdr)))
 			return NF_DROP;
 
 		ipv6_change_dsfield(ipv6_hdr(*pskb), (__u8)(~XT_DSCP_MASK),
diff --git a/net/netfilter/xt_TCPMSS.c b/net/netfilter/xt_TCPMSS.c
index d40f7e4b128..31b6f9d0982 100644
--- a/net/netfilter/xt_TCPMSS.c
+++ b/net/netfilter/xt_TCPMSS.c
@@ -50,7 +50,7 @@ tcpmss_mangle_packet(struct sk_buff **pskb,
 	u16 newmss;
 	u8 *opt;
 
-	if (!skb_make_writable(pskb, (*pskb)->len))
+	if (!skb_make_writable(*pskb, (*pskb)->len))
 		return -1;
 
 	tcplen = (*pskb)->len - tcphoff;