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, 51 insertions, 0 deletions

diff --git a/src/expression.c b/src/expression.c
index b3400751..7ae075d2 100644
--- a/src/expression.c
+++ b/src/expression.c
@@ -1351,6 +1351,56 @@ struct expr *set_elem_catchall_expr_alloc(const struct location *loc)
 	return expr;
 }
 
+static void flagcmp_expr_print(const struct expr *expr, struct output_ctx *octx)
+{
+	expr_print(expr->flagcmp.expr, octx);
+	nft_print(octx, " ");
+	expr_print(expr->flagcmp.value, octx);
+	nft_print(octx, " / ");
+	expr_print(expr->flagcmp.mask, octx);
+}
+
+static void flagcmp_expr_clone(struct expr *new, const struct expr *expr)
+{
+	new->flagcmp.expr = expr_clone(expr->flagcmp.expr);
+	new->flagcmp.mask = expr_clone(expr->flagcmp.mask);
+	new->flagcmp.value = expr_clone(expr->flagcmp.value);
+}
+
+static void flagcmp_expr_destroy(struct expr *expr)
+{
+	expr_free(expr->flagcmp.expr);
+	expr_free(expr->flagcmp.mask);
+	expr_free(expr->flagcmp.value);
+}
+
+static const struct expr_ops flagcmp_expr_ops = {
+	.type		= EXPR_FLAGCMP,
+	.name		= "flags comparison",
+	.print		= flagcmp_expr_print,
+	.json		= flagcmp_expr_json,
+	.clone		= flagcmp_expr_clone,
+	.destroy	= flagcmp_expr_destroy,
+};
+
+struct expr *flagcmp_expr_alloc(const struct location *loc, enum ops op,
+				struct expr *match, struct expr *mask,
+				struct expr *value)
+{
+	struct expr *expr;
+
+	expr = expr_alloc(loc, EXPR_FLAGCMP, match->dtype, match->byteorder,
+			  match->len);
+	expr->op = op;
+	expr->flagcmp.expr = match;
+	expr->flagcmp.mask = mask;
+	/* json output needs this operation for compatibility */
+	expr->flagcmp.mask->op = OP_OR;
+	expr->flagcmp.value = value;
+
+	return expr;
+}
+
 void range_expr_value_low(mpz_t rop, const struct expr *expr)
 {
 	switch (expr->etype) {
@@ -1427,6 +1477,7 @@ static const struct expr_ops *__expr_ops_by_type(enum expr_types etype)
 	case EXPR_FIB: return &fib_expr_ops;
 	case EXPR_XFRM: return &xfrm_expr_ops;
 	case EXPR_SET_ELEM_CATCHALL: return &set_elem_catchall_expr_ops;
+	case EXPR_FLAGCMP: return &flagcmp_expr_ops;
 	}
 
 	BUG("Unknown expression type %d\n", etype);