Patch "netfilter: nft_set_hash: disable fast_ops for 2-len keys" has been added to the 4.13-stable tree

This is a note to let you know that I've just added the patch titled

netfilter: nft_set_hash: disable fast_ops for 2-len keys

to the 4.13-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
netfilter-nft_set_hash-disable-fast_ops-for-2-len-keys.patch
and it can be found in the queue-4.13 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Anatole Denis <[email protected]>
Date: Wed, 4 Oct 2017 01:17:14 +0100
Subject: netfilter: nft_set_hash: disable fast_ops for 2-len keys

From: Anatole Denis <[email protected]>

commit 0414c78f14861cb704d6e6888efd53dd36e3bdde upstream.

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 <port> 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.

---
 net/netfilter/nft_set_hash.c |    1 -
 1 file changed, 1 deletion(-)

@@ -643,7 +643,6 @@ nft_hash_select_ops(const struct nft_ctx
 {
 	if (desc->size) {
 		switch (desc->klen) {
-		case 2:
 		case 4:
 			return &nft_hash_fast_ops;
 		default:

Patches currently in stable-queue which might be from [email protected] are

queue-4.13/netfilter-nft_set_hash-disable-fast_ops-for-2-len-keys.patch