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

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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 5dae9a550a
("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: 5dae9a550a ("genksyms: allow to ignore symbol checksum changes")
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
This commit is contained in:
Masahiro Yamada
2025-01-03 16:30:38 +09:00
parent 5963913bb5
commit 45c9c4101d
2 changed files with 15 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

3
scripts/genksyms/genksyms.c
View File

@@ -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;

14
scripts/genksyms/parse.y
View File

@@ -152,14 +152,19 @@ simple_declaration:
;
init_declarator_list_opt:
/* empty */ { $$ = NULL; }
| init_declarator_list
/* empty */ { $$ = NULL; }
| 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;