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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Wed, 25 Aug 2021 14:55:18 -0700
Message-ID: <CAKwvOdnjaBZiPOD35hxb3SLVpV59mYcDBs=YZBz0KrTisULi9Q@mail.gmail.com>
Subject: Re: [PATCH for-next 17/25] fortify: Fix dropped strcpy() compile-time
 write overflow check
To:     Kees Cook <keescook@chromium.org>
Cc:     linux-kernel@vger.kernel.org, Daniel Axtens <dja@axtens.net>,
        Francis Laniel <laniel_francis@privacyrequired.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Daniel Micay <danielmicay@gmail.com>,
        Bart Van Assche <bvanassche@acm.org>,
        David Gow <davidgow@google.com>, linux-mm@kvack.org,
        clang-built-linux@googlegroups.com, linux-hardening@vger.kernel.org
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On Sun, Aug 22, 2021 at 12:57 AM Kees Cook <keescook@chromium.org> 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@axtens.net>
> Cc: Francis Laniel <laniel_francis@privacyrequired.com>
> Signed-off-by: Kees Cook <keescook@chromium.org>

Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

> ---
>  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