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From: Vasily Khoruzhick <>
To: Pablo Neira Ayuso <>,
	Jozsef Kadlecsik <>,
	Florian Westphal <>,
	"David S. Miller" <>,,,,,
	Dmitry Safonov <>
Cc: Vasily Khoruzhick <>,
Subject: [PATCH] netfilter: conntrack: fix calculation of next bucket number in early_drop
Date: Wed, 24 Oct 2018 20:48:53 -0700	[thread overview]
Message-ID: <> (raw)

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: <> # v4.7+
Signed-off-by: Vasily Khoruzhick <>
 net/netfilter/nf_conntrack_core.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c
index ca1168d67fac..a04af246b184 100644
--- 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;
 	for (i = 0; i < NF_CT_EVICTION_RANGE; i++) {
 		struct hlist_nulls_head *ct_hash;
-		unsigned int hash, hsize, drops;
+		unsigned int bucket, hsize, drops;
 		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]);
 		if (drops) {

             reply	other threads:[~2018-10-25  3:56 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-25  3:48 Vasily Khoruzhick [this message]
2018-10-25  4:52 ` [PATCH] netfilter: conntrack: fix calculation of next bucket number in early_drop Dmitry Safonov
2018-10-25  6:37   ` Vasiliy Khoruzhick

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