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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Vasily Khoruzhick <vasilykh@arista.com>,
        Pablo Neira Ayuso <pablo@netfilter.org>
Subject: [PATCH 4.19 105/205] netfilter: conntrack: fix calculation of next bucket number in early_drop
Date:   Mon, 19 Nov 2018 17:26:52 +0100
Message-Id: <20181119162633.855865262@linuxfoundation.org>
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4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Vasily Khoruzhick <vasilykh@arista.com>

commit f393808dc64149ccd0e5a8427505ba2974a59854 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 net/netfilter/nf_conntrack_core.c |   13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -1073,19 +1073,22 @@ static unsigned int early_drop_list(stru
 	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) {