netfilter: nf_conncount: update last_gc only when GC has been performed

[ Upstream commit 7811ba4 ]

Currently last_gc is being updated everytime a new connection is
tracked, that means that it is updated even if a GC wasn't performed.
With a sufficiently high packet rate, it is possible to always bypass
the GC, causing the list to grow infinitely.

Update the last_gc value only when a GC has been actually performed.

Fixes: d265929 ("netfilter: nf_conncount: reduce unnecessary GC")
Signed-off-by: Fernando Fernandez Mancera <fmancera@suse.de>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: ffmancera

net/netfilter/nf_conncount.c

@@ -229,6 +229,7 @@ static int __nf_conncount_add(struct net *net,
 
 		nf_ct_put(found_ct);
 	}
+	list->last_gc = (u32)jiffies;
 
 add_new_node:
 	if (WARN_ON_ONCE(list->count > INT_MAX)) {
@@ -248,7 +249,6 @@ static int __nf_conncount_add(struct net *net,
 	conn->jiffies32 = (u32)jiffies;
 	list_add_tail(&conn->node, &list->head);
 	list->count++;
-	list->last_gc = (u32)jiffies;
 
 out_put:
 	if (refcounted)