batman-adv: Fix parameter order of hlist_add_behind

1d023284c3 ("list: fix order of arguments for
hlist_add_after(_rcu)") was incorrectly rebased on top of
d9124268d8 ("batman-adv: Fix out-of-order
fragmentation support"). The parameter order change of the rebased patch was
not re-applied as expected. This causes a memory leak and can cause crashes
when out-of-order packets are received. hlist_add_behind will try to access the
uninitalized list pointers of frag_entry_new to find the previous/next entry
and may modify/read random memory locations.

Signed-off-by: Sven Eckelmann <sven@narfation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/batman-adv/fragmentation.c

@@ -188,7 +188,7 @@ static bool batadv_frag_insert_packet(struct batadv_orig_node *orig_node,
 
 	/* Reached the end of the list, so insert after 'frag_entry_last'. */
 	if (likely(frag_entry_last)) {
-		hlist_add_behind(&frag_entry_last->list, &frag_entry_new->list);
+		hlist_add_behind(&frag_entry_new->list, &frag_entry_last->list);
 		chain->size += skb->len - hdr_size;
 		chain->timestamp = jiffies;
 		ret = true;