src: add free_const() and use it instead of xfree()

Almost everywhere xmalloc() and friends is used instead of malloc().
This is almost everywhere paired with xfree().

xfree() has two problems. First, it brings the wrong notion that
xmalloc() should be paired with xfree(), as if xmalloc() would not use
the plain malloc() allocator. In practices, xfree() just wraps free(),
and it wouldn't make sense any other way. xfree() should go away. This
will be addressed in the next commit.

The problem addressed by this commit is that xfree() accepts a const
pointer. Paired with the practice of almost always using xfree() instead
of free(), all our calls to xfree() cast away constness of the pointer,
regardless whether that is necessary. Declaring a pointer as const
should help us to catch wrong uses. If the xfree() function always casts
aways const, the compiler doesn't help.

There are many places that rightly cast away const during free. But not
all of them. Add a free_const() macro, which is like free(), but accepts
const pointers. We should always make an intentional choice whether to
use free() or free_const(). Having a free_const() macro makes this very
common choice clearer, instead of adding a (void*) cast at many places.

Note that we now pair xmalloc() allocations with a free() call (instead
of xfree(). That inconsistency will be resolved in the next commit.

Signed-off-by: Thomas Haller <thaller@redhat.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

13 files changed, 124 insertions, 118 deletions

diff --git a/include/nft.h b/include/nft.h
index 3c894e5b..a2d62dbf 100644
--- a/include/nft.h
+++ b/include/nft.h
@@ -9,4 +9,10 @@
 #include <stdlib.h>
 #include <string.h>
 
+/* Just free(), but casts to a (void*). This is for places where
+ * we have a const pointer that we know we want to free. We could just
+ * do the (void*) cast, but free_const() makes it clear that this is
+ * something we frequently need to do and it's intentional. */
+#define free_const(ptr) free((void *)(ptr))
+
 #endif /* NFTABLES_NFT_H */
diff --git a/src/ct.c b/src/ct.c
index 1dda799d..ebfd90a1 100644
--- a/src/ct.c
+++ b/src/ct.c
@@ -570,7 +570,7 @@ static void flow_offload_stmt_print(const struct stmt *stmt,
 
 static void flow_offload_stmt_destroy(struct stmt *stmt)
 {
-	xfree(stmt->flow.table_name);
+	free_const(stmt->flow.table_name);
 }
 
 static const struct stmt_ops flow_offload_stmt_ops = {
diff --git a/src/datatype.c b/src/datatype.c
index 63627358..ca251138 100644
--- a/src/datatype.c
+++ b/src/datatype.c
@@ -908,8 +908,8 @@ void rt_symbol_table_free(const struct symbol_table *tbl)
 	const struct symbolic_constant *s;
 
 	for (s = tbl->symbols; s->identifier != NULL; s++)
-		xfree(s->identifier);
-	xfree(tbl);
+		free_const(s->identifier);
+	free_const(tbl);
 }
 
 void mark_table_init(struct nft_ctx *ctx)
@@ -1266,8 +1266,8 @@ void datatype_free(const struct datatype *ptr)
 	if (--dtype->refcnt > 0)
 		return;
 
-	xfree(dtype->name);
-	xfree(dtype->desc);
+	free_const(dtype->name);
+	free_const(dtype->desc);
 	xfree(dtype);
 }
 
diff --git a/src/evaluate.c b/src/evaluate.c
index ba6aa300..a2cb4dda 100644
--- a/src/evaluate.c
+++ b/src/evaluate.c
@@ -4027,7 +4027,7 @@ static int stmt_evaluate_chain(struct eval_ctx *ctx, struct stmt *stmt)
 		memset(&h, 0, sizeof(h));
 		handle_merge(&h, &chain->handle);
 		h.family = ctx->rule->handle.family;
-		xfree(h.table.name);
+		free_const(h.table.name);
 		h.table.name = xstrdup(ctx->rule->handle.table.name);
 		h.chain.location = stmt->location;
 		h.chain_id = chain->handle.chain_id;
@@ -4047,9 +4047,9 @@ static int stmt_evaluate_chain(struct eval_ctx *ctx, struct stmt *stmt)
 			struct handle h2 = {};
 
 			handle_merge(&rule->handle, &ctx->rule->handle);
-			xfree(rule->handle.table.name);
+			free_const(rule->handle.table.name);
 			rule->handle.table.name = xstrdup(ctx->rule->handle.table.name);
-			xfree(rule->handle.chain.name);
+			free_const(rule->handle.chain.name);
 			rule->handle.chain.name = NULL;
 			rule->handle.chain_id = chain->handle.chain_id;
 			if (rule_evaluate(&rule_ctx, rule, CMD_INVALID) < 0)
@@ -5152,7 +5152,7 @@ static int ct_timeout_evaluate(struct eval_ctx *ctx, struct obj *obj)
 
 		ct->timeout[ts->timeout_index] = ts->timeout_value;
 		list_del(&ts->head);
-		xfree(ts->timeout_str);
+		free_const(ts->timeout_str);
 		xfree(ts);
 	}
 
diff --git a/src/expression.c b/src/expression.c
index a21dfec2..0b4a537a 100644
--- a/src/expression.c
+++ b/src/expression.c
@@ -314,7 +314,7 @@ static void symbol_expr_clone(struct expr *new, const struct expr *expr)
 
 static void symbol_expr_destroy(struct expr *expr)
 {
-	xfree(expr->identifier);
+	free_const(expr->identifier);
 }
 
 static const struct expr_ops symbol_expr_ops = {
@@ -1335,7 +1335,7 @@ static void set_elem_expr_destroy(struct expr *expr)
 {
 	struct stmt *stmt, *next;
 
-	xfree(expr->comment);
+	free_const(expr->comment);
 	expr_free(expr->key);
 	list_for_each_entry_safe(stmt, next, &expr->stmt_list, list)
 		stmt_free(stmt);
diff --git a/src/libnftables.c b/src/libnftables.c
index 41f54c0c..866b5c6b 100644
--- a/src/libnftables.c
+++ b/src/libnftables.c
@@ -154,8 +154,8 @@ void nft_ctx_clear_vars(struct nft_ctx *ctx)
 	unsigned int i;
 
 	for (i = 0; i < ctx->num_vars; i++) {
-		xfree(ctx->vars[i].key);
-		xfree(ctx->vars[i].value);
+		free_const(ctx->vars[i].key);
+		free_const(ctx->vars[i].value);
 	}
 	ctx->num_vars = 0;
 	xfree(ctx->vars);
@@ -743,12 +743,12 @@ err:
 
 		list_for_each_entry_safe(indesc, next, &nft->vars_ctx.indesc_list, list) {
 			if (indesc->name)
-				xfree(indesc->name);
+				free_const(indesc->name);
 
 			xfree(indesc);
 		}
 	}
-	xfree(nft->vars_ctx.buf);
+	free_const(nft->vars_ctx.buf);
 
 	if (!rc &&
 	    nft_output_json(&nft->output) &&
@@ -799,12 +799,12 @@ int nft_run_cmd_from_filename(struct nft_ctx *nft, const char *filename)
 
 	if (nft->optimize_flags) {
 		ret = nft_run_optimized_file(nft, filename);
-		xfree(nft->stdin_buf);
+		free_const(nft->stdin_buf);
 		return ret;
 	}
 
 	ret = __nft_run_cmd_from_filename(nft, filename);
-	xfree(nft->stdin_buf);
+	free_const(nft->stdin_buf);
 
 	return ret;
 }
diff --git a/src/mnl.c b/src/mnl.c
index 0fb36bd5..0158924c 100644
--- a/src/mnl.c
+++ b/src/mnl.c
@@ -776,9 +776,9 @@ static void nft_dev_array_free(const struct nft_dev *dev_array)
 	int i = 0;
 
 	while (dev_array[i].ifname != NULL)
-		xfree(dev_array[i++].ifname);
+		free_const(dev_array[i++].ifname);
 
-	xfree(dev_array);
+	free_const(dev_array);
 }
 
 static void mnl_nft_chain_devs_build(struct nlmsghdr *nlh, struct cmd *cmd)
@@ -2175,10 +2175,10 @@ static struct basehook *basehook_alloc(void)
 static void basehook_free(struct basehook *b)
 {
 	list_del(&b->list);
-	xfree(b->module_name);
-	xfree(b->hookfn);
-	xfree(b->chain);
-	xfree(b->table);
+	free_const(b->module_name);
+	free_const(b->hookfn);
+	free_const(b->chain);
+	free_const(b->table);
 	xfree(b);
 }
 
diff --git a/src/optimize.c b/src/optimize.c
index 27e0ffe1..9ae9283d 100644
--- a/src/optimize.c
+++ b/src/optimize.c
@@ -1194,7 +1194,7 @@ static void merge_rules(const struct optimize_ctx *ctx,
 	}
 
 	if (ctx->rule[from]->comment) {
-		xfree(ctx->rule[from]->comment);
+		free_const(ctx->rule[from]->comment);
 		ctx->rule[from]->comment = NULL;
 	}
 
diff --git a/src/parser_bison.y b/src/parser_bison.y
index 9bfc3cdb..fdbf307a 100644
--- a/src/parser_bison.y
+++ b/src/parser_bison.y
@@ -154,13 +154,13 @@ static struct expr *ifname_expr_alloc(const struct location *location,
 	struct expr *expr;
 
 	if (length == 0) {
-		xfree(name);
+		free_const(name);
 		erec_queue(error(location, "empty interface name"), queue);
 		return NULL;
 	}
 
 	if (length >= IFNAMSIZ) {
-		xfree(name);
+		free_const(name);
 		erec_queue(error(location, "interface name too long"), queue);
 		return NULL;
 	}
@@ -168,7 +168,7 @@ static struct expr *ifname_expr_alloc(const struct location *location,
 	expr = constant_expr_alloc(location, &ifname_type, BYTEORDER_HOST_ENDIAN,
 				   length * BITS_PER_BYTE, name);
 
-	xfree(name);
+	free_const(name);
 
 	return expr;
 }
@@ -358,7 +358,7 @@ int nft_lex(void *, void *, void *);
 %token <string> STRING		"string"
 %token <string> QUOTED_STRING	"quoted string"
 %token <string> ASTERISK_STRING	"string with a trailing asterisk"
-%destructor { xfree($$); }	STRING QUOTED_STRING ASTERISK_STRING
+%destructor { free_const($$); }	STRING QUOTED_STRING ASTERISK_STRING
 
 %token LL_HDR			"ll"
 %token NETWORK_HDR		"nh"
@@ -674,7 +674,7 @@ int nft_lex(void *, void *, void *);
 %type <limit_rate>		limit_rate_bytes
 
 %type <string>			identifier type_identifier string comment_spec
-%destructor { xfree($$); }	identifier type_identifier string comment_spec
+%destructor { free_const($$); }	identifier type_identifier string comment_spec
 
 %type <val>			time_spec time_spec_or_num_s quota_used
 
@@ -709,7 +709,7 @@ int nft_lex(void *, void *, void *);
 %type <val32>			int_num	chain_policy
 %type <prio_spec>		extended_prio_spec prio_spec
 %type <string>			extended_prio_name quota_unit	basehook_device_name
-%destructor { xfree($$); }	extended_prio_name quota_unit	basehook_device_name
+%destructor { free_const($$); }	extended_prio_name quota_unit	basehook_device_name
 
 %type <expr>			dev_spec
 %destructor { xfree($$); }	dev_spec
@@ -928,7 +928,7 @@ int nft_lex(void *, void *, void *);
 
 %type <val>			markup_format
 %type <string>			monitor_event
-%destructor { xfree($$); }	monitor_event
+%destructor { free_const($$); }	monitor_event
 %type <val>			monitor_object	monitor_format
 
 %type <val>			synproxy_ts	synproxy_sack
@@ -1053,10 +1053,10 @@ close_scope_xt		: { scanner_pop_start_cond(nft->scanner, PARSER_SC_XT); }
 common_block		:	INCLUDE		QUOTED_STRING	stmt_separator
 			{
 				if (scanner_include_file(nft, scanner, $2, &@$) < 0) {
-					xfree($2);
+					free_const($2);
 					YYERROR;
 				}
-				xfree($2);
+				free_const($2);
 			}
 			|	DEFINE		identifier	'='	initializer_expr	stmt_separator
 			{
@@ -1066,19 +1066,19 @@ common_block		:	INCLUDE		QUOTED_STRING	stmt_separator
 					erec_queue(error(&@2, "redefinition of symbol '%s'", $2),
 						   state->msgs);
 					expr_free($4);
-					xfree($2);
+					free_const($2);
 					YYERROR;
 				}
 
 				symbol_bind(scope, $2, $4);
-				xfree($2);
+				free_const($2);
 			}
 			|	REDEFINE	identifier	'='	initializer_expr	stmt_separator
 			{
 				struct scope *scope = current_scope(state);
 
 				symbol_bind(scope, $2, $4);
-				xfree($2);
+				free_const($2);
 			}
 			|	UNDEFINE	identifier	stmt_separator
 			{
@@ -1087,10 +1087,10 @@ common_block		:	INCLUDE		QUOTED_STRING	stmt_separator
 				if (symbol_unbind(scope, $2) < 0) {
 					erec_queue(error(&@2, "undefined symbol '%s'", $2),
 						   state->msgs);
-					xfree($2);
+					free_const($2);
 					YYERROR;
 				}
-				xfree($2);
+				free_const($2);
 			}
 			|	error		stmt_separator
 			{
@@ -1879,21 +1879,21 @@ table_options		:	FLAGS		STRING
 			{
 				if (strcmp($2, "dormant") == 0) {
 					$<table>0->flags |= TABLE_F_DORMANT;
-					xfree($2);
+					free_const($2);
 				} else if (strcmp($2, "owner") == 0) {
 					$<table>0->flags |= TABLE_F_OWNER;
-					xfree($2);
+					free_const($2);
 				} else {
 					erec_queue(error(&@2, "unknown table option %s", $2),
 						   state->msgs);
-					xfree($2);
+					free_const($2);
 					YYERROR;
 				}
 			}
 			|	comment_spec
 			{
 				if (already_set($<table>0->comment, &@$, state)) {
-					xfree($1);
+					free_const($1);
 					YYERROR;
 				}
 				$<table>0->comment = $1;
@@ -2064,7 +2064,7 @@ chain_block		:	/* empty */	{ $$ = $<chain>-1; }
 			|	chain_block	comment_spec	stmt_separator
 			{
 				if (already_set($1->comment, &@2, state)) {
-					xfree($2);
+					free_const($2);
 					YYERROR;
 				}
 				$1->comment = $2;
@@ -2190,7 +2190,7 @@ set_block		:	/* empty */	{ $$ = $<set>-1; }
 			|	set_block	comment_spec	stmt_separator
 			{
 				if (already_set($1->comment, &@2, state)) {
-					xfree($2);
+					free_const($2);
 					YYERROR;
 				}
 				$1->comment = $2;
@@ -2307,7 +2307,7 @@ map_block		:	/* empty */	{ $$ = $<set>-1; }
 			|	map_block	comment_spec	stmt_separator
 			{
 				if (already_set($1->comment, &@2, state)) {
-					xfree($2);
+					free_const($2);
 					YYERROR;
 				}
 				$1->comment = $2;
@@ -2346,10 +2346,10 @@ flowtable_block		:	/* empty */	{ $$ = $<flowtable>-1; }
 				if ($$->hook.name == NULL) {
 					erec_queue(error(&@3, "unknown chain hook"),
 						   state->msgs);
-					xfree($3);
+					free_const($3);
 					YYERROR;
 				}
-				xfree($3);
+				free_const($3);
 
 				$$->priority = $4;
 			}
@@ -2423,12 +2423,12 @@ data_type_atom_expr	:	type_identifier
 				if (dtype == NULL) {
 					erec_queue(error(&@1, "unknown datatype %s", $1),
 						   state->msgs);
-					xfree($1);
+					free_const($1);
 					YYERROR;
 				}
 				$$ = constant_expr_alloc(&@1, dtype, dtype->byteorder,
 							 dtype->size, NULL);
-				xfree($1);
+				free_const($1);
 			}
 			|	TIME
 			{
@@ -2465,7 +2465,7 @@ counter_block		:	/* empty */	{ $$ = $<obj>-1; }
 			|	counter_block	  comment_spec
 			{
 				if (already_set($<obj>1->comment, &@2, state)) {
-					xfree($2);
+					free_const($2);
 					YYERROR;
 				}
 				$<obj>1->comment = $2;
@@ -2482,7 +2482,7 @@ quota_block		:	/* empty */	{ $$ = $<obj>-1; }
 			|	quota_block	comment_spec
 			{
 				if (already_set($<obj>1->comment, &@2, state)) {
-					xfree($2);
+					free_const($2);
 					YYERROR;
 				}
 				$<obj>1->comment = $2;
@@ -2499,7 +2499,7 @@ ct_helper_block		:	/* empty */	{ $$ = $<obj>-1; }
 			|       ct_helper_block     comment_spec
 			{
 				if (already_set($<obj>1->comment, &@2, state)) {
-					xfree($2);
+					free_const($2);
 					YYERROR;
 				}
 				$<obj>1->comment = $2;
@@ -2520,7 +2520,7 @@ ct_timeout_block	:	/*empty */
 			|       ct_timeout_block     comment_spec
 			{
 				if (already_set($<obj>1->comment, &@2, state)) {
-					xfree($2);
+					free_const($2);
 					YYERROR;
 				}
 				$<obj>1->comment = $2;
@@ -2537,7 +2537,7 @@ ct_expect_block		:	/*empty */	{ $$ = $<obj>-1; }
 			|       ct_expect_block     comment_spec
 			{
 				if (already_set($<obj>1->comment, &@2, state)) {
-					xfree($2);
+					free_const($2);
 					YYERROR;
 				}
 				$<obj>1->comment = $2;
@@ -2554,7 +2554,7 @@ limit_block		:	/* empty */	{ $$ = $<obj>-1; }
 			|       limit_block     comment_spec
 			{
 				if (already_set($<obj>1->comment, &@2, state)) {
-					xfree($2);
+					free_const($2);
 					YYERROR;
 				}
 				$<obj>1->comment = $2;
@@ -2571,7 +2571,7 @@ secmark_block		:	/* empty */	{ $$ = $<obj>-1; }
 			|       secmark_block     comment_spec
 			{
 				if (already_set($<obj>1->comment, &@2, state)) {
-					xfree($2);
+					free_const($2);
 					YYERROR;
 				}
 				$<obj>1->comment = $2;
@@ -2588,7 +2588,7 @@ synproxy_block		:	/* empty */	{ $$ = $<obj>-1; }
 			|       synproxy_block     comment_spec
 			{
 				if (already_set($<obj>1->comment, &@2, state)) {
-					xfree($2);
+					free_const($2);
 					YYERROR;
 				}
 				$<obj>1->comment = $2;
@@ -2609,12 +2609,12 @@ hook_spec		:	TYPE		close_scope_type	STRING		HOOK		STRING		dev_spec	prio_spec
 				if (chain_type == NULL) {
 					erec_queue(error(&@3, "unknown chain type"),
 						   state->msgs);
-					xfree($3);
+					free_const($3);
 					YYERROR;
 				}
 				$<chain>0->type.loc = @3;
 				$<chain>0->type.str = xstrdup(chain_type);
-				xfree($3);
+				free_const($3);
 
 				$<chain>0->loc = @$;
 				$<chain>0->hook.loc = @5;
@@ -2622,10 +2622,10 @@ hook_spec		:	TYPE		close_scope_type	STRING		HOOK		STRING		dev_spec	prio_spec
 				if ($<chain>0->hook.name == NULL) {
 					erec_queue(error(&@5, "unknown chain hook"),
 						   state->msgs);
-					xfree($5);
+					free_const($5);
 					YYERROR;
 				}
-				xfree($5);
+				free_const($5);
 
 				$<chain>0->dev_expr	= $6;
 				$<chain>0->priority	= $7;
@@ -2672,7 +2672,7 @@ extended_prio_spec	:	int_num
 								BYTEORDER_HOST_ENDIAN,
 								strlen($1) * BITS_PER_BYTE,
 								$1);
-				xfree($1);
+				free_const($1);
 				$$ = spec;
 			}
 			|	extended_prio_name PLUS NUM
@@ -2685,7 +2685,7 @@ extended_prio_spec	:	int_num
 								BYTEORDER_HOST_ENDIAN,
 								strlen(str) * BITS_PER_BYTE,
 								str);
-				xfree($1);
+				free_const($1);
 				$$ = spec;
 			}
 			|	extended_prio_name DASH NUM
@@ -2698,7 +2698,7 @@ extended_prio_spec	:	int_num
 								BYTEORDER_HOST_ENDIAN,
 								strlen(str) * BITS_PER_BYTE,
 								str);
-				xfree($1);
+				free_const($1);
 				$$ = spec;
 			}
 			;
@@ -2783,7 +2783,7 @@ time_spec		:	STRING
 				uint64_t res;
 
 				erec = time_parse(&@1, $1, &res);
-				xfree($1);
+				free_const($1);
 				if (erec != NULL) {
 					erec_queue(erec, state->msgs);
 					YYERROR;
@@ -2984,7 +2984,7 @@ comment_spec		:	COMMENT		string
 					erec_queue(error(&@2, "comment too long, %d characters maximum allowed",
 							 NFTNL_UDATA_COMMENT_MAXLEN),
 						   state->msgs);
-					xfree($2);
+					free_const($2);
 					YYERROR;
 				}
 				$$ = $2;
@@ -3085,8 +3085,8 @@ stmt			:	verdict_stmt
 xt_stmt			:	XT	STRING	string
 			{
 				$$ = NULL;
-				xfree($2);
-				xfree($3);
+				free_const($2);
+				free_const($3);
 				erec_queue(error(&@$, "unsupported xtables compat expression, use iptables-nft with this ruleset"),
 					   state->msgs);
 				YYERROR;
@@ -3244,7 +3244,7 @@ log_arg			:	PREFIX			string
 					expr = constant_expr_alloc(&@$, &string_type,
 								   BYTEORDER_HOST_ENDIAN,
 								   (strlen($2) + 1) * BITS_PER_BYTE, $2);
-					xfree($2);
+					free_const($2);
 					$<stmt>0->log.prefix = expr;
 					$<stmt>0->log.flags |= STMT_LOG_PREFIX;
 					break;
@@ -3318,7 +3318,7 @@ log_arg			:	PREFIX			string
 									   state->msgs);
 							}
 							expr_free(expr);
-							xfree($2);
+							free_const($2);
 							YYERROR;
 						}
 						item = variable_expr_alloc(&@$, scope, sym);
@@ -3348,7 +3348,7 @@ log_arg			:	PREFIX			string
 					}
 				}
 
-				xfree($2);
+				free_const($2);
 				$<stmt>0->log.prefix	 = expr;
 				$<stmt>0->log.flags 	|= STMT_LOG_PREFIX;
 			}
@@ -3401,10 +3401,10 @@ level_type		:	string
 				else {
 					erec_queue(error(&@1, "invalid log level"),
 						   state->msgs);
-					xfree($1);
+					free_const($1);
 					YYERROR;
 				}
-				xfree($1);
+				free_const($1);
 			}
 			;
 
@@ -3494,7 +3494,7 @@ quota_used		:	/* empty */	{ $$ = 0; }
 				uint64_t rate;
 
 				erec = data_unit_parse(&@$, $3, &rate);
-				xfree($3);
+				free_const($3);
 				if (erec != NULL) {
 					erec_queue(erec, state->msgs);
 					YYERROR;
@@ -3509,7 +3509,7 @@ quota_stmt		:	QUOTA	quota_mode NUM quota_unit quota_used	close_scope_quota
 				uint64_t rate;
 
 				erec = data_unit_parse(&@$, $4, &rate);
-				xfree($4);
+				free_const($4);
 				if (erec != NULL) {
 					erec_queue(erec, state->msgs);
 					YYERROR;
@@ -3553,7 +3553,7 @@ limit_rate_bytes	:	NUM     STRING
 				uint64_t rate, unit;
 
 				erec = rate_parse(&@$, $2, &rate, &unit);
-				xfree($2);
+				free_const($2);
 				if (erec != NULL) {
 					erec_queue(erec, state->msgs);
 					YYERROR;
@@ -3575,7 +3575,7 @@ limit_bytes		:	NUM	BYTES		{ $$ = $1; }
 				uint64_t rate;
 
 				erec = data_unit_parse(&@$, $2, &rate);
-				xfree($2);
+				free_const($2);
 				if (erec != NULL) {
 					erec_queue(erec, state->msgs);
 					YYERROR;
@@ -3604,7 +3604,7 @@ reject_with_expr	:	STRING
 			{
 				$$ = symbol_expr_alloc(&@$, SYMBOL_VALUE,
 						       current_scope(state), $1);
-				xfree($1);
+				free_const($1);
 			}
 			|	integer_expr	{ $$ = $1; }
 			;
@@ -4268,12 +4268,12 @@ variable_expr		:	'$'	identifier
 						erec_queue(error(&@2, "unknown identifier '%s'", $2),
 							   state->msgs);
 					}
-					xfree($2);
+					free_const($2);
 					YYERROR;
 				}
 
 				$$ = variable_expr_alloc(&@$, scope, sym);
-				xfree($2);
+				free_const($2);
 			}
 			;
 
@@ -4283,7 +4283,7 @@ symbol_expr		:	variable_expr
 				$$ = symbol_expr_alloc(&@$, SYMBOL_VALUE,
 						       current_scope(state),
 						       $1);
-				xfree($1);
+				free_const($1);
 			}
 			;
 
@@ -4296,7 +4296,7 @@ set_ref_symbol_expr	:	AT	identifier	close_scope_at
 				$$ = symbol_expr_alloc(&@$, SYMBOL_SET,
 						       current_scope(state),
 						       $2);
-				xfree($2);
+				free_const($2);
 			}
 			;
 
@@ -4393,10 +4393,10 @@ osf_ttl			:	/* empty */
 				else {
 					erec_queue(error(&@2, "invalid ttl option"),
 						   state->msgs);
-					xfree($2);
+					free_const($2);
 					YYERROR;
 				}
-				xfree($2);
+				free_const($2);
 			}
 			;
 
@@ -4566,7 +4566,7 @@ set_elem_option		:	TIMEOUT			time_spec
 			|	comment_spec
 			{
 				if (already_set($<expr>0->comment, &@1, state)) {
-					xfree($1);
+					free_const($1);
 					YYERROR;
 				}
 				$<expr>0->comment = $1;
@@ -4648,7 +4648,7 @@ set_elem_stmt		:	COUNTER	close_scope_counter
 				uint64_t rate;
 
 				erec = data_unit_parse(&@$, $4, &rate);
-				xfree($4);
+				free_const($4);
 				if (erec != NULL) {
 					erec_queue(erec, state->msgs);
 					YYERROR;
@@ -4681,7 +4681,7 @@ set_elem_expr_option	:	TIMEOUT			time_spec
 			|	comment_spec
 			{
 				if (already_set($<expr>0->comment, &@1, state)) {
-					xfree($1);
+					free_const($1);
 					YYERROR;
 				}
 				$<expr>0->comment = $1;
@@ -4733,7 +4733,7 @@ quota_config		:	quota_mode NUM quota_unit quota_used
 				uint64_t rate;
 
 				erec = data_unit_parse(&@$, $3, &rate);
-				xfree($3);
+				free_const($3);
 				if (erec != NULL) {
 					erec_queue(erec, state->msgs);
 					YYERROR;
@@ -4762,10 +4762,10 @@ secmark_config		:	string
 				ret = snprintf(secmark->ctx, sizeof(secmark->ctx), "%s", $1);
 				if (ret <= 0 || ret >= (int)sizeof(secmark->ctx)) {
 					erec_queue(error(&@1, "invalid context '%s', max length is %u\n", $1, (int)sizeof(secmark->ctx)), state->msgs);
-					xfree($1);
+					free_const($1);
 					YYERROR;
 				}
-				xfree($1);
+				free_const($1);
 			}
 			;
 
@@ -4802,7 +4802,7 @@ ct_helper_config		:	TYPE	QUOTED_STRING	PROTOCOL	ct_l4protoname	stmt_separator	cl
 					erec_queue(error(&@2, "invalid name '%s', max length is %u\n", $2, (int)sizeof(ct->name)), state->msgs);
 					YYERROR;
 				}
-				xfree($2);
+				free_const($2);
 
 				ct->l4proto = $4;
 			}
@@ -5197,7 +5197,7 @@ chain_expr		:	variable_expr
 							 BYTEORDER_HOST_ENDIAN,
 							 strlen($1) * BITS_PER_BYTE,
 							 $1);
-				xfree($1);
+				free_const($1);
 			}
 			;
 
@@ -5215,7 +5215,7 @@ meta_expr		:	META	meta_key	close_scope_meta
 				unsigned int key;
 
 				erec = meta_key_parse(&@$, $2, &key);
-				xfree($2);
+				free_const($2);
 				if (erec != NULL) {
 					erec_queue(erec, state->msgs);
 					YYERROR;
@@ -5292,7 +5292,7 @@ meta_stmt		:	META	meta_key	SET	stmt_expr	close_scope_meta
 				unsigned int key;
 
 				erec = meta_key_parse(&@$, $2, &key);
-				xfree($2);
+				free_const($2);
 				if (erec != NULL) {
 					erec_queue(erec, state->msgs);
 					YYERROR;
@@ -5603,10 +5603,10 @@ payload_base_spec	:	LL_HDR		{ $$ = PROTO_BASE_LL_HDR; }
 					$$ = PROTO_BASE_INNER_HDR;
 				} else {
 					erec_queue(error(&@1, "unknown raw payload base"), state->msgs);
-					xfree($1);
+					free_const($1);
 					YYERROR;
 				}
-				xfree($1);
+				free_const($1);
 			}
 			;
 
diff --git a/src/rule.c b/src/rule.c
index 739b7a54..b40a54d7 100644
--- a/src/rule.c
+++ b/src/rule.c
@@ -104,11 +104,11 @@ int timeout_str2num(uint16_t l4proto, struct timeout_state *ts)
 
 void handle_free(struct handle *h)
 {
-	xfree(h->table.name);
-	xfree(h->chain.name);
-	xfree(h->set.name);
-	xfree(h->flowtable.name);
-	xfree(h->obj.name);
+	free_const(h->table.name);
+	free_const(h->chain.name);
+	free_const(h->set.name);
+	free_const(h->flowtable.name);
+	free_const(h->obj.name);
 }
 
 void handle_merge(struct handle *dst, const struct handle *src)
@@ -194,7 +194,7 @@ void set_free(struct set *set)
 
 	expr_free(set->init);
 	if (set->comment)
-		xfree(set->comment);
+		free_const(set->comment);
 	handle_free(&set->handle);
 	list_for_each_entry_safe(stmt, next, &set->stmt_list, list)
 		stmt_free(stmt);
@@ -479,7 +479,7 @@ void rule_free(struct rule *rule)
 		return;
 	stmt_list_free(&rule->stmts);
 	handle_free(&rule->handle);
-	xfree(rule->comment);
+	free_const(rule->comment);
 	xfree(rule);
 }
 
@@ -557,7 +557,7 @@ void scope_release(const struct scope *scope)
 	list_for_each_entry_safe(sym, next, &scope->symbols, list) {
 		assert(sym->refcnt == 1);
 		list_del(&sym->list);
-		xfree(sym->identifier);
+		free_const(sym->identifier);
 		expr_free(sym->expr);
 		xfree(sym);
 	}
@@ -597,7 +597,7 @@ struct symbol *symbol_get(const struct scope *scope, const char *identifier)
 static void symbol_put(struct symbol *sym)
 {
 	if (--sym->refcnt == 0) {
-		xfree(sym->identifier);
+		free_const(sym->identifier);
 		expr_free(sym->expr);
 		xfree(sym);
 	}
@@ -730,14 +730,14 @@ void chain_free(struct chain *chain)
 		rule_free(rule);
 	handle_free(&chain->handle);
 	scope_release(&chain->scope);
-	xfree(chain->type.str);
+	free_const(chain->type.str);
 	expr_free(chain->dev_expr);
 	for (i = 0; i < chain->dev_array_len; i++)
-		xfree(chain->dev_array[i]);
+		free_const(chain->dev_array[i]);
 	xfree(chain->dev_array);
 	expr_free(chain->priority.expr);
 	expr_free(chain->policy);
-	xfree(chain->comment);
+	free_const(chain->comment);
 	xfree(chain);
 }
 
@@ -1151,7 +1151,7 @@ void table_free(struct table *table)
 	if (--table->refcnt > 0)
 		return;
 	if (table->comment)
-		xfree(table->comment);
+		free_const(table->comment);
 	list_for_each_entry_safe(chain, next, &table->chains, list)
 		chain_free(chain);
 	list_for_each_entry_safe(chain, next, &table->chain_bindings, cache.list)
@@ -1348,7 +1348,7 @@ struct monitor *monitor_alloc(uint32_t format, uint32_t type, const char *event)
 
 void monitor_free(struct monitor *m)
 {
-	xfree(m->event);
+	free_const(m->event);
 	xfree(m);
 }
 
@@ -1404,7 +1404,7 @@ void cmd_free(struct cmd *cmd)
 		}
 	}
 	xfree(cmd->attr);
-	xfree(cmd->arg);
+	free_const(cmd->arg);
 	xfree(cmd);
 }
 
@@ -1642,14 +1642,14 @@ void obj_free(struct obj *obj)
 {
 	if (--obj->refcnt > 0)
 		return;
-	xfree(obj->comment);
+	free_const(obj->comment);
 	handle_free(&obj->handle);
 	if (obj->type == NFT_OBJECT_CT_TIMEOUT) {
 		struct timeout_state *ts, *next;
 
 		list_for_each_entry_safe(ts, next, &obj->ct_timeout.timeout_list, head) {
 			list_del(&ts->head);
-			xfree(ts->timeout_str);
+			free_const(ts->timeout_str);
 			xfree(ts);
 		}
 	}
@@ -2062,7 +2062,7 @@ void flowtable_free(struct flowtable *flowtable)
 
 	if (flowtable->dev_array != NULL) {
 		for (i = 0; i < flowtable->dev_array_len; i++)
-			xfree(flowtable->dev_array[i]);
+			free_const(flowtable->dev_array[i]);
 		xfree(flowtable->dev_array);
 	}
 	xfree(flowtable);
diff --git a/src/scanner.l b/src/scanner.l
index 88376b7a..93a31f27 100644
--- a/src/scanner.l
+++ b/src/scanner.l
@@ -1261,8 +1261,8 @@ void *scanner_init(struct parser_state *state)
 static void input_descriptor_destroy(const struct input_descriptor *indesc)
 {
 	if (indesc->name)
-		xfree(indesc->name);
-	xfree(indesc);
+		free_const(indesc->name);
+	free_const(indesc);
 }
 
 static void input_descriptor_list_destroy(struct parser_state *state)
diff --git a/src/statement.c b/src/statement.c
index f5176e6d..994b522c 100644
--- a/src/statement.c
+++ b/src/statement.c
@@ -183,7 +183,7 @@ static void meter_stmt_destroy(struct stmt *stmt)
 	expr_free(stmt->meter.key);
 	expr_free(stmt->meter.set);
 	stmt_free(stmt->meter.stmt);
-	xfree(stmt->meter.name);
+	free_const(stmt->meter.name);
 }
 
 static const struct stmt_ops meter_stmt_ops = {
diff --git a/src/xt.c b/src/xt.c
index 3cb5f028..48b2873b 100644
--- a/src/xt.c
+++ b/src/xt.c
@@ -124,7 +124,7 @@ void xt_stmt_xlate(const struct stmt *stmt, struct output_ctx *octx)
 
 void xt_stmt_destroy(struct stmt *stmt)
 {
-	xfree(stmt->xt.name);
+	free_const(stmt->xt.name);
 	xfree(stmt->xt.info);
 }