netfilter: nf_tables: check if payload length is a power of 2

Add a check if payload's length is a power of 2 when selecting ops.
The fast ops were meant for well aligned loads, also this fixes a
small bug when using a length of 3 with some offsets which causes
only 1 byte to be loaded because the fast ops are chosen.

Signed-off-by: Nikolay Aleksandrov <nikolay@redhat.com>
Acked-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/net/netfilter/nft_payload.c b/net/netfilter/nft_payload.c
index a2aeb318678f..85daa84bfdfe 100644
--- a/net/netfilter/nft_payload.c
+++ b/net/netfilter/nft_payload.c
@@ -135,7 +135,8 @@ nft_payload_select_ops(const struct nft_ctx *ctx,
         if (len == 0 || len > FIELD_SIZEOF(struct nft_data, data))
                 return ERR_PTR(-EINVAL);
 
-        if (len <= 4 && IS_ALIGNED(offset, len) && base != NFT_PAYLOAD_LL_HEADER)
+        if (len <= 4 && is_power_of_2(len) && IS_ALIGNED(offset, len) &&
+            base != NFT_PAYLOAD_LL_HEADER)
                 return &nft_payload_fast_ops;
         else
                 return &nft_payload_ops;