diff mbox series

[1/5] modpost: fix undefined behavior of is_arm_mapping_symbol()

Message ID 20220523164626.858340-1-masahiroy@kernel.org (mailing list archive)
State New
Headers show
Series [1/5] modpost: fix undefined behavior of is_arm_mapping_symbol() | expand

Commit Message

Masahiro Yamada May 23, 2022, 4:46 p.m. UTC
The return value of is_arm_mapping_symbol() is unpredictable when
"$" is passed in.

strchr(3) says:
  The strchr() and strrchr() functions return a pointer to the matched
  character or NULL if the character is not found. The terminating null
  byte is considered part of the string, so that if c is specified as
  '\0', these functions return a pointer to the terminator.

When str[1] is '\0', strchr("axtd", str[1]) is not NULL, and str[2] is
referenced (i.e. buffer overrun).

Test code
---------

  char str1[] = "abc";
  char str2[] = "ab";

  strcpy(str1, "$");
  strcpy(str2, "$");

  printf("test1: %d\n", is_arm_mapping_symbol(str1));
  printf("test2: %d\n", is_arm_mapping_symbol(str2));

Result
------

  test1: 0
  test2: 1

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
---

 scripts/mod/modpost.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Comments

Nick Desaulniers May 24, 2022, 8:42 p.m. UTC | #1
On Mon, May 23, 2022 at 9:48 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> The return value of is_arm_mapping_symbol() is unpredictable when
> "$" is passed in.
>
> strchr(3) says:
>   The strchr() and strrchr() functions return a pointer to the matched
>   character or NULL if the character is not found. The terminating null
>   byte is considered part of the string, so that if c is specified as
>   '\0', these functions return a pointer to the terminator.
>
> When str[1] is '\0', strchr("axtd", str[1]) is not NULL, and str[2] is
> referenced (i.e. buffer overrun).
>
> Test code
> ---------
>
>   char str1[] = "abc";
>   char str2[] = "ab";
>
>   strcpy(str1, "$");
>   strcpy(str2, "$");
>
>   printf("test1: %d\n", is_arm_mapping_symbol(str1));
>   printf("test2: %d\n", is_arm_mapping_symbol(str2));
>
> Result
> ------
>
>   test1: 0
>   test2: 1
>
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

I guess this is shorter than a call to strlen then conditional call to strchr.
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

> ---
>
>  scripts/mod/modpost.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
> index 6f5c605ab0fb..845bc438ca49 100644
> --- a/scripts/mod/modpost.c
> +++ b/scripts/mod/modpost.c
> @@ -1179,7 +1179,8 @@ static int secref_whitelist(const struct sectioncheck *mismatch,
>
>  static inline int is_arm_mapping_symbol(const char *str)
>  {
> -       return str[0] == '$' && strchr("axtd", str[1])
> +       return str[0] == '$' &&
> +              (str[1] == 'a' || str[1] == 'd' || str[1] == 't' || str[1] == 'x')
>                && (str[2] == '\0' || str[2] == '.');
>  }
>
> --
> 2.32.0
>
diff mbox series

Patch

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 6f5c605ab0fb..845bc438ca49 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -1179,7 +1179,8 @@  static int secref_whitelist(const struct sectioncheck *mismatch,
 
 static inline int is_arm_mapping_symbol(const char *str)
 {
-	return str[0] == '$' && strchr("axtd", str[1])
+	return str[0] == '$' &&
+	       (str[1] == 'a' || str[1] == 'd' || str[1] == 't' || str[1] == 'x')
 	       && (str[2] == '\0' || str[2] == '.');
 }