net: disable fragment reassembly if high_thresh is zero

Before commit 6d7b857d541e ("net: use lib/percpu_counter API for
fragmentation mem accounting"), setting the reassembly high threshold
to 0 prevented fragment reassembly as first fragment would be always
evicted before second could be added to the queue. While inefficient,
some users apparently relied on this method.

Since the commit mentioned above, a percpu counter is used for
reassembly memory accounting and high batch size avoids taking slow path
in most common scenarios. As a result, a whole full sized packet can be
reassembled without the percpu counter's main counter changing its value
so that even with high_thresh set to 0, fragmented packets can be still
reassembled and processed.

Add explicit check preventing reassembly if high threshold is zero.

Signed-off-by: Michal Kubecek <mkubecek@suse.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/inet_fragment.c b/net/ipv4/inet_fragment.c
index 3a88b0c73797231e1468de8297045c8ad725ccfa..b5e9317eaf9eea802089dc0c947d88a932ee857a 100644 (file)
--- a/net/ipv4/inet_fragment.c
+++ b/net/ipv4/inet_fragment.c
@@ -355,7 +355,7 @@ static struct inet_frag_queue *inet_frag_alloc(struct netns_frags *nf,
 {
        struct inet_frag_queue *q;
 
-       if (frag_mem_limit(nf) > nf->high_thresh) {
+       if (!nf->high_thresh || frag_mem_limit(nf) > nf->high_thresh) {
                inet_frag_schedule_worker(f);
                return NULL;
        }