parser_bison: add shortcut syntax for matching flags without binary operations

This patch adds the following shortcut syntax:

	expression flags / flags

instead of:

	expression and flags == flags

For example:

	tcp flags syn,ack / syn,ack,fin,rst
                  ^^^^^^^   ^^^^^^^^^^^^^^^
                   value         mask

instead of:

	tcp flags and (syn|ack|fin|rst) == syn|ack

The second list of comma-separated flags represents the mask which are
examined and the first list of comma-separated flags must be set.

You can also use the != operator with this syntax:

	tcp flags != fin,rst / syn,ack,fin,rst

This shortcut is based on the prefix notation, but it is also similar to
the iptables tcp matching syntax.

This patch introduces the flagcmp expression to print the tcp flags in
this new notation. The delinearize path transforms the binary expression
to this new flagcmp expression whenever possible.

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

1 files changed, 17 insertions, 0 deletions

diff --git a/src/evaluate.c b/src/evaluate.c
index 2e31ed10..a3a1d1c0 100644
--- a/src/evaluate.c
+++ b/src/evaluate.c
@@ -2134,6 +2134,21 @@ static int expr_evaluate_xfrm(struct eval_ctx *ctx, struct expr **exprp)
 	return expr_evaluate_primary(ctx, exprp);
 }
 
+static int expr_evaluate_flagcmp(struct eval_ctx *ctx, struct expr **exprp)
+{
+	struct expr *expr = *exprp, *binop, *rel;
+
+	binop = binop_expr_alloc(&expr->location, OP_AND,
+				 expr_get(expr->flagcmp.expr),
+				 expr_get(expr->flagcmp.mask));
+	rel = relational_expr_alloc(&expr->location, expr->op, binop,
+				    expr_get(expr->flagcmp.value));
+	expr_free(expr);
+	*exprp = rel;
+
+	return expr_evaluate(ctx, exprp);
+}
+
 static int expr_evaluate(struct eval_ctx *ctx, struct expr **expr)
 {
 	if (ctx->nft->debug_mask & NFT_DEBUG_EVALUATION) {
@@ -2203,6 +2218,8 @@ static int expr_evaluate(struct eval_ctx *ctx, struct expr **expr)
 		return expr_evaluate_xfrm(ctx, expr);
 	case EXPR_SET_ELEM_CATCHALL:
 		return 0;
+	case EXPR_FLAGCMP:
+		return expr_evaluate_flagcmp(ctx, expr);
 	default:
 		BUG("unknown expression type %s\n", expr_name(*expr));
 	}