[nf-next PATCH v2 2/2] netfilter: nf_tables: Annotate reduced expressions

[Phil Sutter <phil@nwl.cc>]

Introduce NFTA_EXPR_FLAG_REDUCED and set it for expressions which were
omitted from the rule blob due to being redundant. This allows user
space to verify the rule optimizer's results.

Signed-off-by: Phil Sutter <phil@nwl.cc>
---
Changes since v1:
- Keep pointers in struct nft_regs_track const and avoid assigning from
  track.cur to expr instead.
- Fix for situations where nft_expr_reduce() causes skipping of multiple
  expressions (payload + bitwise for instance).
---
 include/uapi/linux/netfilter/nf_tables.h | 7 +++++++
 net/netfilter/nf_tables_api.c            | 8 ++++++--
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/netfilter/nf_tables.h b/include/uapi/linux/netfilter/nf_tables.h
index 36bf019322a44..1da84ebc3f27a 100644
--- a/include/uapi/linux/netfilter/nf_tables.h
+++ b/include/uapi/linux/netfilter/nf_tables.h
@@ -523,6 +523,13 @@ enum nft_expr_attributes {
 };
 #define NFTA_EXPR_MAX		(__NFTA_EXPR_MAX - 1)
 
+/**
+ * NFTA_EXPR_FLAGS values
+ *
+ * @NFTA_EXPR_FLAG_REDUCED: redundant expression omitted from blob
+ */
+#define NFTA_EXPR_FLAG_REDUCED	(1 << 0)
+
 /**
  * enum nft_immediate_attributes - nf_tables immediate expression netlink attributes
  *
diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
index fddc557983119..d4fd32cf74d69 100644
--- a/net/netfilter/nf_tables_api.c
+++ b/net/netfilter/nf_tables_api.c
@@ -8360,8 +8360,8 @@ static bool nft_expr_reduce(struct nft_regs_track *track,
 
 static int nf_tables_commit_chain_prepare(struct net *net, struct nft_chain *chain)
 {
-	const struct nft_expr *expr, *last;
 	struct nft_regs_track track = {};
+	struct nft_expr *expr, *last;
 	unsigned int size, data_size;
 	void *data, *data_boundary;
 	struct nft_rule_dp *prule;
@@ -8404,7 +8404,11 @@ static int nf_tables_commit_chain_prepare(struct net *net, struct nft_chain *cha
 			track.cur = expr;
 
 			if (nft_expr_reduce(&track, expr)) {
-				expr = track.cur;
+				expr->flags |= NFTA_EXPR_FLAG_REDUCED;
+				while (expr != track.cur) {
+					expr = nft_expr_next(expr);
+					expr->flags |= NFTA_EXPR_FLAG_REDUCED;
+				}
 				continue;
 			}
 
-- 
2.34.1