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 5dae9a550a74
("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: 5dae9a550a74 ("genksyms: allow to ignore symbol checksum changes")
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

diff --git a/scripts/genksyms/genksyms.c b/scripts/genksyms/genksyms.c
index 07f9b8cfb23370b385a03ada2becee0e8a2cb3b1..8ca46f807b57aacec3a6b244384f033e102052c5 100644 (file)
--- a/scripts/genksyms/genksyms.c
+++ b/scripts/genksyms/genksyms.c
@@ -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;

diff --git a/scripts/genksyms/parse.y b/scripts/genksyms/parse.y
index 8e9b5e69e8f01da6b71c7f33203d90841118933f..840371d01bf4862c2899e6910051ec28ec04551c 100644 (file)
--- a/scripts/genksyms/parse.y
+++ b/scripts/genksyms/parse.y
@@ -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;