netfilter: conntrack: fix calculation of next bucket number in early_drop

If there's no entry to drop in bucket that corresponds to the hash,
early_drop() should look for it in other buckets. But since it increments
hash instead of bucket number, it actually looks in the same bucket 8
times: hsize is 16k by default (14 bits) and hash is 32-bit value, so
reciprocal_scale(hash, hsize) returns the same value for hash..hash+7 in
most cases.

Fix it by increasing bucket number instead of hash and rename _hash
to bucket to avoid future confusion.

Fixes: 3e86638e9a0b ("netfilter: conntrack: consider ct netns in early_drop logic")
Cc: <stable@vger.kernel.org> # v4.7+
Signed-off-by: Vasily Khoruzhick <vasilykh@arista.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index ca1168d67fac6c0fc1eaef5dfeb1db8428e51db3..e92e749aff53e46c60718b55593e72d70838e9be 100644 (file)
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -1073,19 +1073,22 @@ static unsigned int early_drop_list(struct net *net,
        return drops;
 }
 
-static noinline int early_drop(struct net *net, unsigned int _hash)
+static noinline int early_drop(struct net *net, unsigned int hash)
 {
-       unsigned int i;
+       unsigned int i, bucket;
 
        for (i = 0; i < NF_CT_EVICTION_RANGE; i++) {
                struct hlist_nulls_head *ct_hash;
-               unsigned int hash, hsize, drops;
+               unsigned int hsize, drops;
 
                rcu_read_lock();
                nf_conntrack_get_ht(&ct_hash, &hsize);
-               hash = reciprocal_scale(_hash++, hsize);
+               if (!i)
+                       bucket = reciprocal_scale(hash, hsize);
+               else
+                       bucket = (bucket + 1) % hsize;
 
-               drops = early_drop_list(net, &ct_hash[hash]);
+               drops = early_drop_list(net, &ct_hash[bucket]);
                rcu_read_unlock();
 
                if (drops) {