src: add refcount asserts

_get() functions must not be used when refcnt is 0, as expr_free()
releases expressions on 1 -> 0 transition.

Also, check that a refcount would not overflow from UINT_MAX to 0.
Use INT_MAX to also catch refcount leaks sooner, we don't expect
2**31 get()s on same object.

This helps catching use-after-free refcounting bugs even when nft
is built without ASAN support.

v3: use a macro + BUG to get more info without a coredump.

Signed-off-by: Florian Westphal <fw@strlen.de>

2 files changed, 19 insertions, 0 deletions

diff --git a/src/expression.c b/src/expression.c
index 019c263f..6c7bebe0 100644
--- a/src/expression.c
+++ b/src/expression.c
@@ -68,6 +68,7 @@ struct expr *expr_clone(const struct expr *expr)
 
 struct expr *expr_get(struct expr *expr)
 {
+	assert_refcount_safe(expr->refcnt);
 	expr->refcnt++;
 	return expr;
 }
@@ -84,6 +85,8 @@ void expr_free(struct expr *expr)
 {
 	if (expr == NULL)
 		return;
+
+	assert_refcount_safe(expr->refcnt);
 	if (--expr->refcnt > 0)
 		return;
 
@@ -343,11 +346,13 @@ static void variable_expr_clone(struct expr *new, const struct expr *expr)
 	new->scope      = expr->scope;
 	new->sym	= expr->sym;
 
+	assert_refcount_safe(expr->sym->refcnt);
 	expr->sym->refcnt++;
 }
 
 static void variable_expr_destroy(struct expr *expr)
 {
+	assert_refcount_safe(expr->sym->refcnt);
 	expr->sym->refcnt--;
 }
 
diff --git a/src/rule.c b/src/rule.c
index d0a62a3e..f51d605c 100644
--- a/src/rule.c
+++ b/src/rule.c
@@ -181,6 +181,7 @@ struct set *set_clone(const struct set *set)
 
 struct set *set_get(struct set *set)
 {
+	assert_refcount_safe(set->refcnt);
 	set->refcnt++;
 	return set;
 }
@@ -189,6 +190,7 @@ void set_free(struct set *set)
 {
 	struct stmt *stmt, *next;
 
+	assert_refcount_safe(set->refcnt);
 	if (--set->refcnt > 0)
 		return;
 
@@ -484,12 +486,14 @@ struct rule *rule_alloc(const struct location *loc, const struct handle *h)
 
 struct rule *rule_get(struct rule *rule)
 {
+	assert_refcount_safe(rule->refcnt);
 	rule->refcnt++;
 	return rule;
 }
 
 void rule_free(struct rule *rule)
 {
+	assert_refcount_safe(rule->refcnt);
 	if (--rule->refcnt > 0)
 		return;
 	stmt_list_free(&rule->stmts);
@@ -606,6 +610,7 @@ struct symbol *symbol_get(const struct scope *scope, const char *identifier)
 	if (!sym)
 		return NULL;
 
+	assert_refcount_safe(sym->refcnt);
 	sym->refcnt++;
 
 	return sym;
@@ -613,6 +618,7 @@ struct symbol *symbol_get(const struct scope *scope, const char *identifier)
 
 static void symbol_put(struct symbol *sym)
 {
+	assert_refcount_safe(sym->refcnt);
 	if (--sym->refcnt == 0) {
 		free_const(sym->identifier);
 		expr_free(sym->expr);
@@ -732,6 +738,7 @@ struct chain *chain_alloc(void)
 
 struct chain *chain_get(struct chain *chain)
 {
+	assert_refcount_safe(chain->refcnt);
 	chain->refcnt++;
 	return chain;
 }
@@ -741,6 +748,7 @@ void chain_free(struct chain *chain)
 	struct rule *rule, *next;
 	int i;
 
+	assert_refcount_safe(chain->refcnt);
 	if (--chain->refcnt > 0)
 		return;
 	list_for_each_entry_safe(rule, next, &chain->rules, list)
@@ -1176,6 +1184,7 @@ void table_free(struct table *table)
 	struct set *set, *nset;
 	struct obj *obj, *nobj;
 
+	assert_refcount_safe(table->refcnt);
 	if (--table->refcnt > 0)
 		return;
 	if (table->comment)
@@ -1214,6 +1223,7 @@ void table_free(struct table *table)
 
 struct table *table_get(struct table *table)
 {
+	assert_refcount_safe(table->refcnt);
 	table->refcnt++;
 	return table;
 }
@@ -1687,12 +1697,14 @@ struct obj *obj_alloc(const struct location *loc)
 
 struct obj *obj_get(struct obj *obj)
 {
+	assert_refcount_safe(obj->refcnt);
 	obj->refcnt++;
 	return obj;
 }
 
 void obj_free(struct obj *obj)
 {
+	assert_refcount_safe(obj->refcnt);
 	if (--obj->refcnt > 0)
 		return;
 	free_const(obj->comment);
@@ -2270,6 +2282,7 @@ struct flowtable *flowtable_alloc(const struct location *loc)
 
 struct flowtable *flowtable_get(struct flowtable *flowtable)
 {
+	assert_refcount_safe(flowtable->refcnt);
 	flowtable->refcnt++;
 	return flowtable;
 }
@@ -2278,6 +2291,7 @@ void flowtable_free(struct flowtable *flowtable)
 {
 	int i;
 
+	assert_refcount_safe(flowtable->refcnt);
 	if (--flowtable->refcnt > 0)
 		return;
 	handle_free(&flowtable->handle);