[PATCH nf] netfilter: nf_tables: cancel register tracking if .reduce is not defined

[Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>]

Cancel all register tracking if the the reduce function is not defined.
Add missing reduce function to cmp since this is a read-only operation.

This unbreaks selftests/netfilter/nft_nat_zones.sh.

Fixes: 12e4ecfa244b ("netfilter: nf_tables: add register tracking infrastructure")
Suggested-by: Florian Westphal <fw@xxxxxxxxx>
Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
---
 net/netfilter/nf_tables_api.c | 2 ++
 net/netfilter/nft_cmp.c       | 8 ++++++++
 2 files changed, 10 insertions(+)

diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
index c86748b3873b..861a3a36024a 100644
--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -8311,6 +8311,8 @@ static int nf_tables_commit_chain_prepare(struct net *net, struct nft_chain *cha
 			    expr->ops->reduce(&track, expr)) {
 				expr = track.cur;
 				continue;
+			} else if (expr->ops->reduce == NULL) {
+				memset(track.regs, 0, sizeof(track.regs));
 			}
 
 			if (WARN_ON_ONCE(data + expr->ops->size > data_boundary))
diff --git a/net/netfilter/nft_cmp.c b/net/netfilter/nft_cmp.c
index 47b6d05f1ae6..23bef7df48f1 100644
--- a/net/netfilter/nft_cmp.c
+++ b/net/netfilter/nft_cmp.c
@@ -187,12 +187,19 @@ static int nft_cmp_offload(struct nft_offload_ctx *ctx,
 	return __nft_cmp_offload(ctx, flow, priv);
 }
 
+static bool nft_cmp_reduce(struct nft_regs_track *track,
+			   const struct nft_expr *expr)
+{
+	return false;
+}
+
 static const struct nft_expr_ops nft_cmp_ops = {
 	.type		= &nft_cmp_type,
 	.size		= NFT_EXPR_SIZE(sizeof(struct nft_cmp_expr)),
 	.eval		= nft_cmp_eval,
 	.init		= nft_cmp_init,
 	.dump		= nft_cmp_dump,
+	.reduce		= nft_cmp_reduce,
 	.offload	= nft_cmp_offload,
 };
 
@@ -269,6 +276,7 @@ const struct nft_expr_ops nft_cmp_fast_ops = {
 	.eval		= NULL,	/* inlined */
 	.init		= nft_cmp_fast_init,
 	.dump		= nft_cmp_fast_dump,
+	.reduce		= nft_cmp_reduce,
 	.offload	= nft_cmp_fast_offload,
 };
 
-- 
2.30.2