Re: [PATCH for-next 17/25] fortify: Fix dropped strcpy() compile-time write overflow check

[Nick Desaulniers]

On Sun, Aug 22, 2021 at 12:57 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>
> The implementation for intra-object overflow in str*-family functions
> accidentally dropped compile-time write overflow checking in strcpy(),
> leaving it entirely to run-time. Add back the intended check.
>
> Fixes: 6a39e62abbaf ("lib: string.h: detect intra-object overflow in fortified string functions")
> Cc: Daniel Axtens <dja@xxxxxxxxxx>
> Cc: Francis Laniel <laniel_francis@xxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>

Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>

> ---
>  include/linux/fortify-string.h | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h
> index 7e67d02764db..68bc5978d916 100644
> --- a/include/linux/fortify-string.h
> +++ b/include/linux/fortify-string.h
> @@ -287,7 +287,10 @@ __FORTIFY_INLINE char *strcpy(char *p, const char *q)
>         if (p_size == (size_t)-1 && q_size == (size_t)-1)
>                 return __underlying_strcpy(p, q);
>         size = strlen(q) + 1;
> -       /* test here to use the more stringent object size */
> +       /* Compile-time check for const size overflow. */
> +       if (__builtin_constant_p(size) && p_size < size)
> +               __write_overflow();
> +       /* Run-time check for dynamic size overflow. */
>         if (p_size < size)
>                 fortify_panic(__func__);
>         memcpy(p, q, size);
> --
> 2.30.2
>
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-- 
Thanks,
~Nick Desaulniers