Re: [PATCH v2 04/10] fortify: Use const variables for __member_size tracking

[Nick Desaulniers]

On Fri, Apr 7, 2023 at 12:27 PM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>
> The sizes reported by __member_size should never change in a given
> function. Mark them as such.
>
> Suggested-by: Miguel Ojeda <miguel.ojeda.sandonis@xxxxxxxxx>
> Cc: linux-hardening@xxxxxxxxxxxxxxx
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>

Thanks for the patch!
Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>

> ---
>  include/linux/fortify-string.h | 42 +++++++++++++++++-----------------
>  1 file changed, 21 insertions(+), 21 deletions(-)
>
> diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h
> index c9de1f59ee80..fae1bf4bd543 100644
> --- a/include/linux/fortify-string.h
> +++ b/include/linux/fortify-string.h
> @@ -20,7 +20,7 @@ void __write_overflow_field(size_t avail, size_t wanted) __compiletime_warning("
>  ({                                                             \
>         char *__p = (char *)(p);                                \
>         size_t __ret = SIZE_MAX;                                \
> -       size_t __p_size = __member_size(p);                     \
> +       const size_t __p_size = __member_size(p);               \
>         if (__p_size != SIZE_MAX &&                             \
>             __builtin_constant_p(*__p)) {                       \
>                 size_t __p_len = __p_size - 1;                  \
> @@ -142,7 +142,7 @@ extern char *__underlying_strncpy(char *p, const char *q, __kernel_size_t size)
>  __FORTIFY_INLINE __diagnose_as(__builtin_strncpy, 1, 2, 3)
>  char *strncpy(char * const POS p, const char *q, __kernel_size_t size)
>  {
> -       size_t p_size = __member_size(p);
> +       const size_t p_size = __member_size(p);
>
>         if (__compiletime_lessthan(p_size, size))
>                 __write_overflow();
> @@ -169,7 +169,7 @@ char *strncpy(char * const POS p, const char *q, __kernel_size_t size)
>  __FORTIFY_INLINE __diagnose_as(__builtin_strcat, 1, 2)
>  char *strcat(char * const POS p, const char *q)
>  {
> -       size_t p_size = __member_size(p);
> +       const size_t p_size = __member_size(p);
>
>         if (p_size == SIZE_MAX)
>                 return __underlying_strcat(p, q);
> @@ -191,8 +191,8 @@ extern __kernel_size_t __real_strnlen(const char *, __kernel_size_t) __RENAME(st
>   */
>  __FORTIFY_INLINE __kernel_size_t strnlen(const char * const POS p, __kernel_size_t maxlen)
>  {
> -       size_t p_size = __member_size(p);
> -       size_t p_len = __compiletime_strlen(p);
> +       const size_t p_size = __member_size(p);
> +       const size_t p_len = __compiletime_strlen(p);
>         size_t ret;
>
>         /* We can take compile-time actions when maxlen is const. */
> @@ -233,8 +233,8 @@ __FORTIFY_INLINE __kernel_size_t strnlen(const char * const POS p, __kernel_size
>  __FORTIFY_INLINE __diagnose_as(__builtin_strlen, 1)
>  __kernel_size_t __fortify_strlen(const char * const POS p)
>  {
> +       const size_t p_size = __member_size(p);
>         __kernel_size_t ret;
> -       size_t p_size = __member_size(p);
>
>         /* Give up if we don't know how large p is. */
>         if (p_size == SIZE_MAX)
> @@ -267,8 +267,8 @@ extern size_t __real_strlcpy(char *, const char *, size_t) __RENAME(strlcpy);
>   */
>  __FORTIFY_INLINE size_t strlcpy(char * const POS p, const char * const POS q, size_t size)
>  {
> -       size_t p_size = __member_size(p);
> -       size_t q_size = __member_size(q);
> +       const size_t p_size = __member_size(p);
> +       const size_t q_size = __member_size(q);
>         size_t q_len;   /* Full count of source string length. */
>         size_t len;     /* Count of characters going into destination. */
>
> @@ -318,10 +318,10 @@ extern ssize_t __real_strscpy(char *, const char *, size_t) __RENAME(strscpy);
>   */
>  __FORTIFY_INLINE ssize_t strscpy(char * const POS p, const char * const POS q, size_t size)
>  {
> -       size_t len;
>         /* Use string size rather than possible enclosing struct size. */
> -       size_t p_size = __member_size(p);
> -       size_t q_size = __member_size(q);
> +       const size_t p_size = __member_size(p);
> +       const size_t q_size = __member_size(q);
> +       size_t len;
>
>         /* If we cannot get size of p and q default to call strscpy. */
>         if (p_size == SIZE_MAX && q_size == SIZE_MAX)
> @@ -394,9 +394,9 @@ __FORTIFY_INLINE ssize_t strscpy(char * const POS p, const char * const POS q, s
>  __FORTIFY_INLINE __diagnose_as(__builtin_strncat, 1, 2, 3)
>  char *strncat(char * const POS p, const char * const POS q, __kernel_size_t count)
>  {
> +       const size_t p_size = __member_size(p);
> +       const size_t q_size = __member_size(q);
>         size_t p_len, copy_len;
> -       size_t p_size = __member_size(p);
> -       size_t q_size = __member_size(q);
>
>         if (p_size == SIZE_MAX && q_size == SIZE_MAX)
>                 return __underlying_strncat(p, q, count);
> @@ -639,7 +639,7 @@ __FORTIFY_INLINE bool fortify_memcpy_chk(__kernel_size_t size,
>  extern void *__real_memscan(void *, int, __kernel_size_t) __RENAME(memscan);
>  __FORTIFY_INLINE void *memscan(void * const POS0 p, int c, __kernel_size_t size)
>  {
> -       size_t p_size = __struct_size(p);
> +       const size_t p_size = __struct_size(p);
>
>         if (__compiletime_lessthan(p_size, size))
>                 __read_overflow();
> @@ -651,8 +651,8 @@ __FORTIFY_INLINE void *memscan(void * const POS0 p, int c, __kernel_size_t size)
>  __FORTIFY_INLINE __diagnose_as(__builtin_memcmp, 1, 2, 3)
>  int memcmp(const void * const POS0 p, const void * const POS0 q, __kernel_size_t size)
>  {
> -       size_t p_size = __struct_size(p);
> -       size_t q_size = __struct_size(q);
> +       const size_t p_size = __struct_size(p);
> +       const size_t q_size = __struct_size(q);
>
>         if (__builtin_constant_p(size)) {
>                 if (__compiletime_lessthan(p_size, size))
> @@ -668,7 +668,7 @@ int memcmp(const void * const POS0 p, const void * const POS0 q, __kernel_size_t
>  __FORTIFY_INLINE __diagnose_as(__builtin_memchr, 1, 2, 3)
>  void *memchr(const void * const POS0 p, int c, __kernel_size_t size)
>  {
> -       size_t p_size = __struct_size(p);
> +       const size_t p_size = __struct_size(p);
>
>         if (__compiletime_lessthan(p_size, size))
>                 __read_overflow();
> @@ -680,7 +680,7 @@ void *memchr(const void * const POS0 p, int c, __kernel_size_t size)
>  void *__real_memchr_inv(const void *s, int c, size_t n) __RENAME(memchr_inv);
>  __FORTIFY_INLINE void *memchr_inv(const void * const POS0 p, int c, size_t size)
>  {
> -       size_t p_size = __struct_size(p);
> +       const size_t p_size = __struct_size(p);
>
>         if (__compiletime_lessthan(p_size, size))
>                 __read_overflow();
> @@ -693,7 +693,7 @@ extern void *__real_kmemdup(const void *src, size_t len, gfp_t gfp) __RENAME(kme
>                                                                     __realloc_size(2);
>  __FORTIFY_INLINE void *kmemdup(const void * const POS0 p, size_t size, gfp_t gfp)
>  {
> -       size_t p_size = __struct_size(p);
> +       const size_t p_size = __struct_size(p);
>
>         if (__compiletime_lessthan(p_size, size))
>                 __read_overflow();
> @@ -720,8 +720,8 @@ __FORTIFY_INLINE void *kmemdup(const void * const POS0 p, size_t size, gfp_t gfp
>  __FORTIFY_INLINE __diagnose_as(__builtin_strcpy, 1, 2)
>  char *strcpy(char * const POS p, const char * const POS q)
>  {
> -       size_t p_size = __member_size(p);
> -       size_t q_size = __member_size(q);
> +       const size_t p_size = __member_size(p);
> +       const size_t q_size = __member_size(q);
>         size_t size;
>
>         /* If neither buffer size is known, immediately give up. */
> --
> 2.34.1
>


-- 
Thanks,
~Nick Desaulniers