Commit 45c9c410 authored Jan 03, 2025 by Masahiro Yamada

genksyms: fix memory leak when the same symbol is added from source

When a symbol that is already registered is added again, __add_symbol()
returns without freeing the symbol definition, making it unreachable.

The following test cases demonstrate different memory leak points.

[Test Case 1]

Forward declaration with exactly the same definition

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

[Test Case 2]

Forward declaration with a different definition (e.g. attribute)

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

[Test Case 3]

Preserving an overridden symbol (compile with KBUILD_PRESERVE=1)

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

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

The memory leaks in Test Case 1 and 2 have existed since the introduction
of genksyms into the kernel tree. [1]

The memory leak in Test Case 3 was introduced by commit 5dae9a55
("genksyms: allow to ignore symbol checksum changes").

When multiple init_declarators are reduced to an init_declarator_list,
the decl_spec must be duplicated. Otherwise, the following Test Case 4
would result in a double-free bug.

[Test Case 4]

  $ cat foo.c
  #include <linux/export.h>

  extern int foo, bar;

  int foo, bar;
  EXPORT_SYMBOL(foo);

In this case, 'foo' and 'bar' share the same decl_spec, 'int'. It must
be unshared before being passed to add_symbol().

[1]: https://git.kernel.org/pub/scm/linux/kernel/git/history/history.git/commit/?id=46bd1da672d66ccd8a639d3c1f8a166048cca608



Fixes: 5dae9a55 ("genksyms: allow to ignore symbol checksum changes")
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

parent 5963913b

scripts/genksyms/genksyms.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -239,6 +239,7 @@ static struct symbol __add_symbol(const char name, enum symbol_type type,
		"unchanged\n");
		}
		sym->is_declared = 1;
		free_list(defn, NULL);
		return sym;
		} else if (!sym->is_declared) {
		if (sym->is_override && flag_preserve) {
		@@ -247,6 +248,7 @@ static struct symbol __add_symbol(const char name, enum symbol_type type,
		print_type_name(type, name);
		fprintf(stderr, " modversion change\n");
		sym->is_declared = 1;
		free_list(defn, NULL);
		return sym;
		} else {
		status = is_unknown_symbol(sym) ?
		@@ -254,6 +256,7 @@ static struct symbol __add_symbol(const char name, enum symbol_type type,
		}
		} else {
		error_with_pos("redefinition of %s", name);
		free_list(defn, NULL);
		return sym;
		}
		break;

scripts/genksyms/parse.y

+12 −2

Original line number	Diff line number	Diff line
		@@ -153,13 +153,18 @@ simple_declaration:

		init_declarator_list_opt:
		/* empty */ { $$ = NULL; }
		\| init_declarator_list
		\| init_declarator_list { free_list(decl_spec, NULL); $$ = $1; }
		;

		init_declarator_list:
		init_declarator
		{ struct string_list decl = $1;
		*$1 = NULL;

		/* avoid sharing among multiple init_declarators */
		if (decl_spec)
		decl_spec = copy_list_range(decl_spec, NULL);

		add_symbol(current_name,
		is_typedef ? SYM_TYPEDEF : SYM_NORMAL, decl, is_extern);
		current_name = NULL;
		@@ -170,6 +175,11 @@ init_declarator_list:
		*$3 = NULL;
		free_list(*$2, NULL);
		*$2 = decl_spec;

		/* avoid sharing among multiple init_declarators */
		if (decl_spec)
		decl_spec = copy_list_range(decl_spec, NULL);

		add_symbol(current_name,
		is_typedef ? SYM_TYPEDEF : SYM_NORMAL, decl, is_extern);
		current_name = NULL;