src: add tcp options set support

This adds support for tcp mss mangling:

nft add rule filter input tcp option maxseg size 1200

Its also possible to change other tcp option fields, but
maxseg is one of the more useful ones to change.

Signed-off-by: Florian Westphal <fw@strlen.de>
Acked-by: Pablo Neira Ayuso <pablo@netfilter.org>

1 files changed, 29 insertions, 0 deletions

diff --git a/src/netlink_linearize.c b/src/netlink_linearize.c
index 3d684569..c5a47dec 100644
--- a/src/netlink_linearize.c
+++ b/src/netlink_linearize.c
@@ -816,6 +816,33 @@ static bool payload_needs_l4csum_update_pseudohdr(const struct expr *expr,
 	return false;
 }
 
+static void netlink_gen_exthdr_stmt(struct netlink_linearize_ctx *ctx,
+				    const struct stmt *stmt)
+{
+	struct nftnl_expr *nle;
+	const struct expr *expr;
+	enum nft_registers sreg;
+	unsigned int offset;
+
+	sreg = get_register(ctx, stmt->exthdr.val);
+	netlink_gen_expr(ctx, stmt->exthdr.val, sreg);
+	release_register(ctx, stmt->exthdr.val);
+
+	expr = stmt->exthdr.expr;
+
+	offset = expr->exthdr.tmpl->offset + expr->exthdr.offset;
+
+	nle = alloc_nft_expr("exthdr");
+	netlink_put_register(nle, NFTNL_EXPR_EXTHDR_SREG, sreg);
+	nftnl_expr_set_u8(nle, NFTNL_EXPR_EXTHDR_TYPE,
+			  expr->exthdr.desc->type);
+	nftnl_expr_set_u32(nle, NFTNL_EXPR_EXTHDR_OFFSET, offset / BITS_PER_BYTE);
+	nftnl_expr_set_u32(nle, NFTNL_EXPR_EXTHDR_LEN,
+			   div_round_up(expr->len, BITS_PER_BYTE));
+	nftnl_expr_set_u8(nle, NFTNL_EXPR_EXTHDR_OP, expr->exthdr.op);
+	nftnl_rule_add_expr(ctx->nlr, nle);
+}
+
 static void netlink_gen_payload_stmt(struct netlink_linearize_ctx *ctx,
 				     const struct stmt *stmt)
 {
@@ -1239,6 +1266,8 @@ static void netlink_gen_stmt(struct netlink_linearize_ctx *ctx,
 		return netlink_gen_verdict_stmt(ctx, stmt);
 	case STMT_FLOW:
 		return netlink_gen_flow_stmt(ctx, stmt);
+	case STMT_EXTHDR:
+		return netlink_gen_exthdr_stmt(ctx, stmt);
 	case STMT_PAYLOAD:
 		return netlink_gen_payload_stmt(ctx, stmt);
 	case STMT_META: