From 0414c78f14861cb704d6e6888efd53dd36e3bdde Mon Sep 17 00:00:00 2001 From: Anatole Denis Date: Wed, 4 Oct 2017 01:17:14 +0100 Subject: [PATCH] netfilter: nft_set_hash: disable fast_ops for 2-len keys jhash_1word of a u16 is a different value from jhash of the same u16 with length 2. Since elements are always inserted in sets using jhash over the actual klen, this would lead to incorrect lookups on fixed-size sets with a key length of 2, as they would be inserted with hash value jhash(key, 2) and looked up with hash value jhash_1word(key), which is different. Example reproducer(v4.13+), using anonymous sets which always have a fixed size: table inet t { chain c { type filter hook output priority 0; policy accept; tcp dport { 10001, 10003, 10005, 10007, 10009 } counter packets 4 bytes 240 reject tcp dport 10001 counter packets 4 bytes 240 reject tcp dport 10003 counter packets 4 bytes 240 reject tcp dport 10005 counter packets 4 bytes 240 reject tcp dport 10007 counter packets 0 bytes 0 reject tcp dport 10009 counter packets 4 bytes 240 reject } } then use nc -z localhost to probe; incorrectly hashed ports will pass through the set lookup and increment the counter of an individual rule. jhash being seeded with a random value, it is not deterministic which ports will incorrectly hash, but in testing with 5 ports in the set I always had 4 or 5 with an incorrect hash value. Signed-off-by: Anatole Denis Signed-off-by: Pablo Neira Ayuso --- net/netfilter/nft_set_hash.c | 1 - 1 file changed, 1 deletion(-) diff --git a/net/netfilter/nft_set_hash.c b/net/netfilter/nft_set_hash.c index 0fa01d7..9c0d5a7 100644 --- a/net/netfilter/nft_set_hash.c +++ b/net/netfilter/nft_set_hash.c @@ -643,7 +643,6 @@ nft_hash_select_ops(const struct nft_ctx *ctx, const struct nft_set_desc *desc, { if (desc->size) { switch (desc->klen) { - case 2: case 4: return &nft_hash_fast_ops; default: -- 2.7.4