xt_psd: move L4 header fetching into helper

Also start splitting psd_match into two functions, one to do initial
sanity checking and header retrieval, one to do the actual work.

extensions/xt_psd.c

@@ -214,52 +214,36 @@ static void remove_oldest(struct host **head, struct host *curr)
 		ht_unlink(head, last);
 }
 
-static bool
+static void *
-xt_psd_match(const struct sk_buff *pskb, struct xt_action_param *match)
+get_header_pointer4(const struct sk_buff *skb, unsigned int thoff, void *mem)
+{
+	const struct iphdr *iph = ip_hdr(skb);
+	int hdrlen;
+
+	switch (iph->protocol) {
+	case IPPROTO_TCP:
+		hdrlen = sizeof(struct tcphdr);
+		break;
+	case IPPROTO_UDP:
+	case IPPROTO_UDPLITE:
+		hdrlen = sizeof(struct udphdr);
+		break;
+	default:
+		return NULL;
+	}
+
+	return skb_header_pointer(skb, thoff, hdrlen, mem);
+}
+
+static bool
+handle_packet4(const struct iphdr *iph, const struct tcphdr *tcph,
+               const struct xt_psd_info *psdinfo)
 {
-	const struct iphdr *iph;
-	const struct tcphdr *tcph = NULL;
-	union {
-		struct tcphdr tcph;
-		struct udphdr udph;
-	} _buf;
-	u_int8_t proto;
 	unsigned long now;
 	struct host *curr, *last = NULL, **head;
 	struct host4 *curr4;
 	int count = 0;
 	unsigned int hash;
-	/* Parameters from userspace */
-	const struct xt_psd_info *psdinfo = match->matchinfo;
-
-	iph = ip_hdr(pskb);
-	if (iph->frag_off & htons(IP_OFFSET)) {
-		pr_debug("sanity check failed\n");
-		return false;
-	}
-
-	proto = iph->protocol;
-	/* We're using IP address 0.0.0.0 for a special purpose here, so don't let
-	 * them spoof us. [DHCP needs this feature - HW] */
-	if (iph->saddr == 0) {
-		pr_debug("spoofed source address (0.0.0.0)\n");
-		return false;
-	}
-
-	if (proto == IPPROTO_TCP) {
-		tcph = skb_header_pointer(pskb, match->thoff,
-		       sizeof(_buf.tcph), &_buf.tcph);
-		if (tcph == NULL)
-			return false;
-	} else if (proto == IPPROTO_UDP || proto == IPPROTO_UDPLITE) {
-		tcph = skb_header_pointer(pskb, match->thoff,
-		       sizeof(_buf.udph), &_buf.udph);
-		if (tcph == NULL)
-			return false;
-	} else {
-		pr_debug("protocol not supported\n");
-		return false;
-	}
 
 	now = jiffies;
 	hash = hashfunc(iph->saddr);
@@ -280,7 +264,7 @@ xt_psd_match(const struct sk_buff *pskb, struct xt_action_param *match)
 	if (curr != NULL) {
 		/* We know this address, and the entry isn't too old. Update it. */
 		if (entry_is_recent(curr, psdinfo->delay_threshold, now)) {
-			if (is_portscan(curr, psdinfo, tcph, proto))
+			if (is_portscan(curr, psdinfo, tcph, iph->protocol))
 				goto out_match;
 			goto out_no_match;
 		}
@@ -294,7 +278,7 @@ xt_psd_match(const struct sk_buff *pskb, struct xt_action_param *match)
 	}
 
 	/* We don't need an ACK from a new source address */
-	if (proto == IPPROTO_TCP && tcph->ack)
+	if (iph->protocol == IPPROTO_TCP && tcph->ack)
 		goto out_no_match;
 
 	/* Got too many source addresses with the same hash value? Then remove the
@@ -327,7 +311,7 @@ xt_psd_match(const struct sk_buff *pskb, struct xt_action_param *match)
 	curr->count = 1;
 	curr->weight = get_port_weight(psdinfo, tcph->dest);
 	curr->ports[0].number = tcph->dest;
-	curr->ports[0].proto = proto;
+	curr->ports[0].proto = iph->protocol;
 
 out_no_match:
 	spin_unlock(&state.lock);
@@ -338,6 +322,36 @@ out_match:
 	return true;
 }
 
+static bool
+xt_psd_match(const struct sk_buff *pskb, struct xt_action_param *match)
+{
+	struct iphdr *iph = ip_hdr(pskb);
+	struct tcphdr _tcph;
+	struct tcphdr *tcph;
+	/* Parameters from userspace */
+	const struct xt_psd_info *psdinfo = match->matchinfo;
+
+	if (iph->frag_off & htons(IP_OFFSET)) {
+		pr_debug("sanity check failed\n");
+		return false;
+	}
+
+	/*
+	 * We are using IP address 0.0.0.0 for a special purpose here, so do
+	 * not let them spoof us. [DHCP needs this feature - HW]
+	 */
+	if (iph->saddr == 0) {
+		pr_debug("spoofed source address (0.0.0.0)\n");
+		return false;
+	}
+
+	tcph = get_header_pointer4(pskb, match->thoff, &_tcph);
+	if (tcph == NULL)
+		return false;
+
+	return handle_packet4(iph, tcph, psdinfo);
+}
+
 static int psd_mt_check(const struct xt_mtchk_param *par)
 {
 	const struct xt_psd_info *info = par->matchinfo;