src: allow to use variables in flowtable and chain devices

This patch adds support for using variables for devices in the chain and
flowtable definitions, eg.

 define if_main = lo

 table netdev filter1 {
    chain Main_Ingress1 {
        type filter hook ingress device $if_main priority -500; policy accept;
    }
 }

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

2 files changed, 85 insertions, 0 deletions

diff --git a/src/evaluate.c b/src/evaluate.c
index 67eb5d60..c9601f17 100644
--- a/src/evaluate.c
+++ b/src/evaluate.c
@@ -3719,6 +3719,69 @@ static bool evaluate_priority(struct eval_ctx *ctx, struct prio_spec *prio,
 	return true;
 }
 
+static bool evaluate_expr_variable(struct eval_ctx *ctx, struct expr **exprp)
+{
+	struct expr *expr;
+
+	if (expr_evaluate(ctx, exprp) < 0)
+		return false;
+
+	expr = *exprp;
+	if (expr->etype != EXPR_VALUE &&
+	    expr->etype != EXPR_SET) {
+		expr_error(ctx->msgs, expr, "%s is not a valid "
+			   "variable expression", expr_name(expr));
+		return false;
+	}
+
+	return true;
+}
+
+static bool evaluate_device_expr(struct eval_ctx *ctx, struct expr **dev_expr)
+{
+	struct expr *expr, *next, *key;
+	LIST_HEAD(tmp);
+
+	if ((*dev_expr)->etype == EXPR_VARIABLE) {
+		expr_set_context(&ctx->ectx, &ifname_type,
+				 IFNAMSIZ * BITS_PER_BYTE);
+		if (!evaluate_expr_variable(ctx, dev_expr))
+			return false;
+	}
+
+	if ((*dev_expr)->etype != EXPR_SET &&
+	    (*dev_expr)->etype != EXPR_LIST)
+		return true;
+
+	list_for_each_entry_safe(expr, next, &(*dev_expr)->expressions, list) {
+		list_del(&expr->list);
+
+		switch (expr->etype) {
+		case EXPR_VARIABLE:
+			expr_set_context(&ctx->ectx, &ifname_type,
+					 IFNAMSIZ * BITS_PER_BYTE);
+			if (!evaluate_expr_variable(ctx, &expr))
+				return false;
+			break;
+		case EXPR_SET_ELEM:
+			key = expr_clone(expr->key);
+			expr_free(expr);
+			expr = key;
+			break;
+		case EXPR_VALUE:
+			break;
+		default:
+			BUG("invalid expresion type %s\n", expr_name(expr));
+			break;
+		}
+
+		list_add(&expr->list, &tmp);
+	}
+	list_splice_init(&tmp, &(*dev_expr)->expressions);
+
+	return true;
+}
+
 static uint32_t str2hooknum(uint32_t family, const char *hook);
 
 static int flowtable_evaluate(struct eval_ctx *ctx, struct flowtable *ft)
@@ -3740,6 +3803,9 @@ static int flowtable_evaluate(struct eval_ctx *ctx, struct flowtable *ft)
 						   expr_name(ft->priority.expr));
 	}
 
+	if (ft->dev_expr && !evaluate_device_expr(ctx, &ft->dev_expr))
+		return -1;
+
 	return 0;
 }
 
@@ -3965,6 +4031,9 @@ static int chain_evaluate(struct eval_ctx *ctx, struct chain *chain)
 			if (!chain->dev_expr)
 				return __stmt_binary_error(ctx, &chain->loc, NULL,
 							   "Missing `device' in this chain definition");
+
+			if (!evaluate_device_expr(ctx, &chain->dev_expr))
+				return -1;
 		} else if (chain->dev_expr) {
 			return __stmt_binary_error(ctx, &chain->dev_expr->location, NULL,
 						   "This chain type cannot be bound to device");
diff --git a/src/parser_bison.y b/src/parser_bison.y
index 572e584c..d2d7694a 100644
--- a/src/parser_bison.y
+++ b/src/parser_bison.y
@@ -1945,6 +1945,11 @@ flowtable_expr		:	'{'	flowtable_list_expr	'}'
 				$2->location = @$;
 				$$ = $2;
 			}
+			|	variable_expr
+			{
+				$1->location = @$;
+				$$ = $1;
+			}
 			;
 
 flowtable_list_expr	:	flowtable_expr_member
@@ -1967,6 +1972,11 @@ flowtable_expr_member	:	STRING
 							 strlen($1) * BITS_PER_BYTE, $1);
 				xfree($1);
 			}
+			|	variable_expr
+			{
+				datatype_set($1->sym->expr, &ifname_type);
+				$$ = $1;
+			}
 			;
 
 data_type_atom_expr	:	type_identifier
@@ -2206,6 +2216,12 @@ dev_spec		:	DEVICE	string
 				compound_expr_add($$, expr);
 
 			}
+			|	DEVICE	variable_expr
+			{
+				datatype_set($2->sym->expr, &ifname_type);
+				$$ = compound_expr_alloc(&@$, EXPR_LIST);
+				compound_expr_add($$, $2);
+			}
 			|	DEVICES		'='	flowtable_expr
 			{
 				$$ = $3;