batman-adv: Use only queued fragments when merging

The fragment queueing code now validates the total_size of each fragment,
checks when enough fragments are queued to allow to merge them into a
single packet and if the fragments have the correct size. Therefore, it is
not required to have any other parameter for the merging function than a
list of queued fragments.

This change should avoid problems like in the past when the different skb
from the list and the function parameter were mixed incorrectly.

Signed-off-by: Sven Eckelmann <sven@narfation.org>
Acked-by: Martin Hundebøll <martin@hundeboll.net>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>

net/batman-adv/fragmentation.c

@@ -231,19 +231,13 @@ err:
  * Returns the merged skb or NULL on error.
  */
 static struct sk_buff *
-batadv_frag_merge_packets(struct hlist_head *chain, struct sk_buff *skb)
+batadv_frag_merge_packets(struct hlist_head *chain)
 {
 	struct batadv_frag_packet *packet;
 	struct batadv_frag_list_entry *entry;
 	struct sk_buff *skb_out = NULL;
 	int size, hdr_size = sizeof(struct batadv_frag_packet);
 
-	/* Make sure incoming skb has non-bogus data. */
-	packet = (struct batadv_frag_packet *)skb->data;
-	size = ntohs(packet->total_size);
-	if (size > batadv_frag_size_limit())
-		goto free;
-
 	/* Remove first entry, as this is the destination for the rest of the
 	 * fragments.
 	 */
@@ -252,6 +246,9 @@ batadv_frag_merge_packets(struct hlist_head *chain, struct sk_buff *skb)
 	skb_out = entry->skb;
 	kfree(entry);
 
+	packet = (struct batadv_frag_packet *)skb_out->data;
+	size = ntohs(packet->total_size);
+
 	/* Make room for the rest of the fragments. */
 	if (pskb_expand_head(skb_out, 0, size - skb_out->len, GFP_ATOMIC) < 0) {
 		kfree_skb(skb_out);
@@ -307,7 +304,7 @@ bool batadv_frag_skb_buffer(struct sk_buff **skb,
 	if (hlist_empty(&head))
 		goto out;
 
-	skb_out = batadv_frag_merge_packets(&head, *skb);
+	skb_out = batadv_frag_merge_packets(&head);
 	if (!skb_out)
 		goto out_err;