Added undefine/redefine keywords

This is a small patch to nft which adds two new keywords - undefine and
redefine. undefine simply undefines a variable from the current scope.
redefine allows one to change a variable definition. We have a firewall
written in bash (using iptables) that is organized by customer VLANs.
Each VLAN has its own set of bash variables holding things like uplink
iface names, gateway IPs, etc. We want to rewrite the firewall to
nftables but are stuck on the fact that nft variables cannot be
overridden in the same scope. We have each VLAN configuration in a
separate file containing pre/post-routing, input, output and forward
rules,and we include those files to a master firewall configuration. One
solution is to rename all the variables with some VLAN specific
(pre/su)ffix. But that is cumbersome.

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

3 files changed, 39 insertions, 0 deletions

diff --git a/src/parser_bison.y b/src/parser_bison.y
index ec8b0dd8..df672b1e 100644
--- a/src/parser_bison.y
+++ b/src/parser_bison.y
@@ -185,6 +185,8 @@ int nft_lex(void *, void *, void *);
 
 %token INCLUDE			"include"
 %token DEFINE			"define"
+%token REDEFINE			"redefine"
+%token UNDEFINE			"undefine"
 
 %token FIB			"fib"
 
@@ -763,6 +765,26 @@ common_block		:	INCLUDE		QUOTED_STRING	stmt_separator
 				symbol_bind(scope, $2, $4);
 				xfree($2);
 			}
+			|	REDEFINE	identifier	'='	initializer_expr	stmt_separator
+			{
+				struct scope *scope = current_scope(state);
+
+				/* ignore missing identifier */
+				symbol_unbind(scope, $2);
+				symbol_bind(scope, $2, $4);
+				xfree($2);
+			}
+			|	UNDEFINE	identifier	stmt_separator
+			{
+				struct scope *scope = current_scope(state);
+
+				if (symbol_unbind(scope, $2) < 0) {
+					erec_queue(error(&@2, "undefined symbol '%s'", $2),
+						   state->msgs);
+					YYERROR;
+				}
+				xfree($2);
+			}
 			|	error		stmt_separator
 			{
 				if (++state->nerrs == nft->parser_max_errors)
diff --git a/src/rule.c b/src/rule.c
index c7b4b498..5b7219e8 100644
--- a/src/rule.c
+++ b/src/rule.c
@@ -485,6 +485,21 @@ void symbol_bind(struct scope *scope, const char *identifier, struct expr *expr)
 	list_add_tail(&sym->list, &scope->symbols);
 }
 
+int symbol_unbind(struct scope *scope, const char *identifier)
+{
+	struct symbol *sym;
+
+	sym = symbol_lookup(scope, identifier);
+	if (!sym)
+		return -1;
+
+	list_del(&sym->list);
+	xfree(sym->identifier);
+	expr_free(sym->expr);
+	xfree(sym);
+	return 0;
+}
+
 struct symbol *symbol_lookup(const struct scope *scope, const char *identifier)
 {
 	struct symbol *sym;
diff --git a/src/scanner.l b/src/scanner.l
index c3992a78..05c70afe 100644
--- a/src/scanner.l
+++ b/src/scanner.l
@@ -233,6 +233,8 @@ addrstring	({macaddr}|{ip4addr}|{ip6addr})
 
 "include"		{ return INCLUDE; }
 "define"		{ return DEFINE; }
+"redefine"		{ return REDEFINE; }
+"undefine"		{ return UNDEFINE; }
 
 "describe"		{ return DESCRIBE; }