ipv4: share tcp_v4_save_options() with cookie_v4_check()

cookie_v4_check() allocates ip_options_rcu in the same way
with tcp_v4_save_options(), we can just make it a helper function.

Cc: Krzysztof Kolasa <[e-mail]>
Cc: Eric Dumazet <[e-mail]>
Signed-off-by: Cong Wang <[e-mail]>
Signed-off-by: Cong Wang <[e-mail]>
Acked-by: Eric Dumazet <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/tcp.h

···
 void tcp_v4_init(void);
 void tcp_init(void);
 
+/*
+ * Save and compile IPv4 options, return a pointer to it
+ */
+static inline struct ip_options_rcu *tcp_v4_save_options(struct sk_buff *skb)
+{
+	const struct ip_options *opt = &TCP_SKB_CB(skb)->header.h4.opt;
+	struct ip_options_rcu *dopt = NULL;
+
+	if (opt && opt->optlen) {
+		int opt_size = sizeof(*dopt) + opt->optlen;
+
+		dopt = kmalloc(opt_size, GFP_ATOMIC);
+		if (dopt && __ip_options_echo(&dopt->opt, skb, opt)) {
+			kfree(dopt);
+			dopt = NULL;
+		}
+	}
+	return dopt;
+}
+
 #endif	/* _TCP_H */

net/ipv4/syncookies.c

···
 	/* We throwed the options of the initial SYN away, so we hope
 	 * the ACK carries the same options again (see RFC1122 4.2.3.8)
 	 */
-	if (opt && opt->optlen) {
-		int opt_size = sizeof(struct ip_options_rcu) + opt->optlen;
-
-		ireq->opt = kmalloc(opt_size, GFP_ATOMIC);
-		if (ireq->opt != NULL && __ip_options_echo(&ireq->opt->opt, skb, opt)) {
-			kfree(ireq->opt);
-			ireq->opt = NULL;
-		}
-	}
+	ireq->opt = tcp_v4_save_options(skb);
 
 	if (security_inet_conn_request(sk, skb, req)) {
 		reqsk_free(req);

net/ipv4/tcp_ipv4.c

···
 }
 EXPORT_SYMBOL(tcp_syn_flood_action);
 
-/*
- * Save and compile IPv4 options into the request_sock if needed.
- */
-static struct ip_options_rcu *tcp_v4_save_options(struct sk_buff *skb)
-{
-	const struct ip_options *opt = &TCP_SKB_CB(skb)->header.h4.opt;
-	struct ip_options_rcu *dopt = NULL;
-
-	if (opt && opt->optlen) {
-		int opt_size = sizeof(*dopt) + opt->optlen;
-
-		dopt = kmalloc(opt_size, GFP_ATOMIC);
-		if (dopt && __ip_options_echo(&dopt->opt, skb, opt)) {
-			kfree(dopt);
-			dopt = NULL;
-		}
-	}
-	return dopt;
-}
-
 #ifdef CONFIG_TCP_MD5SIG
 /*
  * RFC2385 MD5 checksumming requires a mapping of