consolidate duplicate code is skb_checksum_setup() helpers

consolidate duplicate code is skb_checksum_setup() helpers

Realizing that the skb_maybe_pull_tail() calls in the IP-protocol
specific portions of both helpers are terminal ones (i.e. no further
pulls are expected), their maximum size to be pulled can be made match
their minimal size needed, thus making the code identical and hence
possible to be moved into another helper.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Cc: Paul Durrant <paul.durrant@citrix.com>
Cc: David Miller <davem@davemloft.net>
Cc: Eric Dumazet <edumazet@google.com>
Reviewed-by: Paul Durrant <paul.durrant@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/skbuff.c

@@ -3566,15 +3566,47 @@ static int skb_maybe_pull_tail(struct sk_buff *skb, unsigned int len,
 	return 0;
 }
 
+#define MAX_TCP_HDR_LEN (15 * 4)
+
+static __sum16 *skb_checksum_setup_ip(struct sk_buff *skb,
+				      typeof(IPPROTO_IP) proto,
+				      unsigned int off)
+{
+	switch (proto) {
+		int err;
+
+	case IPPROTO_TCP:
+		err = skb_maybe_pull_tail(skb, off + sizeof(struct tcphdr),
+					  off + MAX_TCP_HDR_LEN);
+		if (!err && !skb_partial_csum_set(skb, off,
+						  offsetof(struct tcphdr,
+							   check)))
+			err = -EPROTO;
+		return err ? ERR_PTR(err) : &tcp_hdr(skb)->check;
+
+	case IPPROTO_UDP:
+		err = skb_maybe_pull_tail(skb, off + sizeof(struct udphdr),
+					  off + sizeof(struct udphdr));
+		if (!err && !skb_partial_csum_set(skb, off,
+						  offsetof(struct udphdr,
+							   check)))
+			err = -EPROTO;
+		return err ? ERR_PTR(err) : &udp_hdr(skb)->check;
+	}
+
+	return ERR_PTR(-EPROTO);
+}
+
 /* This value should be large enough to cover a tagged ethernet header plus
  * maximally sized IP and TCP or UDP headers.
  */
 #define MAX_IP_HDR_LEN 128
 
-static int skb_checksum_setup_ip(struct sk_buff *skb, bool recalculate)
+static int skb_checksum_setup_ipv4(struct sk_buff *skb, bool recalculate)
 {
 	unsigned int off;
 	bool fragment;
+	__sum16 *csum;
 	int err;
 
 	fragment = false;
@@ -3595,51 +3627,15 @@ static int skb_checksum_setup_ip(struct sk_buff *skb, bool recalculate)
 	if (fragment)
 		goto out;
 
-	switch (ip_hdr(skb)->protocol) {
-	case IPPROTO_TCP:
-		err = skb_maybe_pull_tail(skb,
-					  off + sizeof(struct tcphdr),
-					  MAX_IP_HDR_LEN);
-		if (err < 0)
-			goto out;
-
-		if (!skb_partial_csum_set(skb, off,
-					  offsetof(struct tcphdr, check))) {
-			err = -EPROTO;
-			goto out;
-		}
-
-		if (recalculate)
-			tcp_hdr(skb)->check =
-				~csum_tcpudp_magic(ip_hdr(skb)->saddr,
-						   ip_hdr(skb)->daddr,
-						   skb->len - off,
-						   IPPROTO_TCP, 0);
-		break;
-	case IPPROTO_UDP:
-		err = skb_maybe_pull_tail(skb,
-					  off + sizeof(struct udphdr),
-					  MAX_IP_HDR_LEN);
-		if (err < 0)
-			goto out;
-
-		if (!skb_partial_csum_set(skb, off,
-					  offsetof(struct udphdr, check))) {
-			err = -EPROTO;
-			goto out;
-		}
-
-		if (recalculate)
-			udp_hdr(skb)->check =
-				~csum_tcpudp_magic(ip_hdr(skb)->saddr,
-						   ip_hdr(skb)->daddr,
-						   skb->len - off,
-						   IPPROTO_UDP, 0);
-		break;
-	default:
-		goto out;
-	}
+	csum = skb_checksum_setup_ip(skb, ip_hdr(skb)->protocol, off);
+	if (IS_ERR(csum))
+		return PTR_ERR(csum);
 
+	if (recalculate)
+		*csum = ~csum_tcpudp_magic(ip_hdr(skb)->saddr,
+					   ip_hdr(skb)->daddr,
+					   skb->len - off,
+					   ip_hdr(skb)->protocol, 0);
 	err = 0;
 
 out:
@@ -3662,6 +3658,7 @@ static int skb_checksum_setup_ipv6(struct sk_buff *skb, bool recalculate)
 	unsigned int len;
 	bool fragment;
 	bool done;
+	__sum16 *csum;
 
 	fragment = false;
 	done = false;
@@ -3739,51 +3736,14 @@ static int skb_checksum_setup_ipv6(struct sk_buff *skb, bool recalculate)
 	if (!done || fragment)
 		goto out;
 
-	switch (nexthdr) {
-	case IPPROTO_TCP:
-		err = skb_maybe_pull_tail(skb,
-					  off + sizeof(struct tcphdr),
-					  MAX_IPV6_HDR_LEN);
-		if (err < 0)
-			goto out;
-
-		if (!skb_partial_csum_set(skb, off,
-					  offsetof(struct tcphdr, check))) {
-			err = -EPROTO;
-			goto out;
-		}
-
-		if (recalculate)
-			tcp_hdr(skb)->check =
-				~csum_ipv6_magic(&ipv6_hdr(skb)->saddr,
-						 &ipv6_hdr(skb)->daddr,
-						 skb->len - off,
-						 IPPROTO_TCP, 0);
-		break;
-	case IPPROTO_UDP:
-		err = skb_maybe_pull_tail(skb,
-					  off + sizeof(struct udphdr),
-					  MAX_IPV6_HDR_LEN);
-		if (err < 0)
-			goto out;
-
-		if (!skb_partial_csum_set(skb, off,
-					  offsetof(struct udphdr, check))) {
-			err = -EPROTO;
-			goto out;
-		}
-
-		if (recalculate)
-			udp_hdr(skb)->check =
-				~csum_ipv6_magic(&ipv6_hdr(skb)->saddr,
-						 &ipv6_hdr(skb)->daddr,
-						 skb->len - off,
-						 IPPROTO_UDP, 0);
-		break;
-	default:
-		goto out;
-	}
+	csum = skb_checksum_setup_ip(skb, nexthdr, off);
+	if (IS_ERR(csum))
+		return PTR_ERR(csum);
 
+	if (recalculate)
+		*csum = ~csum_ipv6_magic(&ipv6_hdr(skb)->saddr,
+					 &ipv6_hdr(skb)->daddr,
+					 skb->len - off, nexthdr, 0);
 	err = 0;
 
 out:
@@ -3801,7 +3761,7 @@ int skb_checksum_setup(struct sk_buff *skb, bool recalculate)
 
 	switch (skb->protocol) {
 	case htons(ETH_P_IP):
-		err = skb_checksum_setup_ip(skb, recalculate);
+		err = skb_checksum_setup_ipv4(skb, recalculate);
 		break;
 
 	case htons(ETH_P_IPV6):