genksyms: fix memory leak when the same symbol is read from *.symref …

…file

When a symbol that is already registered is read again from *.symref
file, __add_symbol() removes the previous one from the hash table without
freeing it.

[Test Case]

  $ cat foo.c
  #include <linux/export.h>
  void foo(void);
  void foo(void) {}
  EXPORT_SYMBOL(foo);

  $ cat foo.symref
  foo void foo ( void )
  foo void foo ( void )

When a symbol is removed from the hash table, it must be freed along
with its ->name and ->defn members. However, sym->name cannot be freed
because it is sometimes shared with node->string, but not always. If
sym->name and node->string share the same memory, free(sym->name) could
lead to a double-free bug.

To resolve this issue, always assign a strdup'ed string to sym->name.

Fixes: 64e6c1e ("genksyms: track symbol checksum changes")
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

scripts/genksyms/genksyms.c

@@ -272,11 +272,15 @@ static struct symbol *__add_symbol(const char *name, enum symbol_type type,
 				break;
 			}
 		}
+
+		free_list(sym->defn, NULL);
+		free(sym->name);
+		free(sym);
 		--nsyms;
 	}
 
 	sym = xmalloc(sizeof(*sym));
-	sym->name = name;
+	sym->name = xstrdup(name);
 	sym->type = type;
 	sym->defn = defn;
 	sym->expansion_trail = NULL;
@@ -483,7 +487,7 @@ static void read_reference(FILE *f)
 			defn = def;
 			def = read_node(f);
 		}
-		subsym = add_reference_symbol(xstrdup(sym->string), sym->tag,
+		subsym = add_reference_symbol(sym->string, sym->tag,
 					      defn, is_extern);
 		subsym->is_override = is_override;
 		free_node(sym);

scripts/genksyms/genksyms.h

@@ -32,7 +32,7 @@ struct string_list {
 
 struct symbol {
 	struct symbol *hash_next;
-	const char *name;
+	char *name;
 	enum symbol_type type;
 	struct string_list *defn;
 	struct symbol *expansion_trail;

scripts/genksyms/parse.y

@@ -482,12 +482,12 @@ enumerator_list:
 enumerator:
 	IDENT
 		{
-			const char *name = strdup((*$1)->string);
+			const char *name = (*$1)->string;
 			add_symbol(name, SYM_ENUM_CONST, NULL, 0);
 		}
 	| IDENT '=' EXPRESSION_PHRASE
 		{
-			const char *name = strdup((*$1)->string);
+			const char *name = (*$1)->string;
 			struct string_list *expr = copy_list_range(*$3, *$2);
 			add_symbol(name, SYM_ENUM_CONST, expr, 0);
 		}