netfilter: nft_bitwise: track register operations

Check if the destination register already contains the data that this
bitwise expression performs. This allows to skip this redundant
operation.

If the destination contains a different bitwise operation, cancel the
register tracking information. If the destination contains no bitwise
operation, update the register tracking information.

Update the payload and meta expression to check if this bitwise
operation has been already performed on the register. Hence, both the
payload/meta and the bitwise expressions are reduced.

There is also a special case: If source register != destination register
and source register is not updated by a previous bitwise operation, then
transfer selector from the source register to the destination register.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/net/netfilter/nf_tables.h b/include/net/netfilter/nf_tables.h
index 1c37ce61daea..eaf55da9a205 100644
--- a/include/net/netfilter/nf_tables.h
+++ b/include/net/netfilter/nf_tables.h
@@ -358,6 +358,8 @@ int nft_expr_clone(struct nft_expr *dst, struct nft_expr *src);
 void nft_expr_destroy(const struct nft_ctx *ctx, struct nft_expr *expr);
 int nft_expr_dump(struct sk_buff *skb, unsigned int attr,
 		  const struct nft_expr *expr);
+bool nft_expr_reduce_bitwise(struct nft_regs_track *track,
+			     const struct nft_expr *expr);
 
 struct nft_set_ext;