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Message-ID: <201907231435.FABB1CC@keescook>
Date: Tue, 23 Jul 2019 14:36:25 -0700
From: Kees Cook <keescook@...omium.org>
To: Joe Perches <joe@...ches.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
linux-kernel@...r.kernel.org, Jonathan Corbet <corbet@....net>,
Stephen Kitt <steve@....org>, Nitin Gote <nitin.r.gote@...el.com>,
jannh@...gle.com, kernel-hardening@...ts.openwall.com,
Rasmus Villemoes <rasmus.villemoes@...vas.dk>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/2] string: Add stracpy and stracpy_pad mechanisms
On Mon, Jul 22, 2019 at 05:38:15PM -0700, Joe Perches wrote:
> Several uses of strlcpy and strscpy have had defects because the
> last argument of each function is misused or typoed.
>
> Add macro mechanisms to avoid this defect.
>
> stracpy (copy a string to a string array) must have a string
> array as the first argument (to) and uses sizeof(to) as the
> size.
>
> These mechanisms verify that the to argument is an array of
> char or other compatible types like u8 or unsigned char.
>
> A BUILD_BUG is emitted when the type of to is not compatible.
>
> Signed-off-by: Joe Perches <joe@...ches.com>
I think Rasmus's suggestion would make sense:
BUILD_BUG_ON(!__same_type(typeof(to), char[]))
Either way, I think it should be fine:
Reviewed-by: Kees Cook <keescook@...omium.org>
-Kees
> ---
> include/linux/string.h | 41 +++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 41 insertions(+)
>
> diff --git a/include/linux/string.h b/include/linux/string.h
> index 4deb11f7976b..f80b0973f0e5 100644
> --- a/include/linux/string.h
> +++ b/include/linux/string.h
> @@ -35,6 +35,47 @@ ssize_t strscpy(char *, const char *, size_t);
> /* Wraps calls to strscpy()/memset(), no arch specific code required */
> ssize_t strscpy_pad(char *dest, const char *src, size_t count);
>
> +/**
> + * stracpy - Copy a C-string into an array of char
> + * @to: Where to copy the string, must be an array of char and not a pointer
> + * @from: String to copy, may be a pointer or const char array
> + *
> + * Helper for strscpy.
> + * Copies a maximum of sizeof(@to) bytes of @from with %NUL termination.
> + *
> + * Returns:
> + * * The number of characters copied (not including the trailing %NUL)
> + * * -E2BIG if @to is a zero size array.
> + */
> +#define stracpy(to, from) \
> +({ \
> + size_t size = ARRAY_SIZE(to); \
> + BUILD_BUG_ON(!__same_type(typeof(*to), char)); \
> + \
> + strscpy(to, from, size); \
> +})
> +
> +/**
> + * stracpy_pad - Copy a C-string into an array of char with %NUL padding
> + * @to: Where to copy the string, must be an array of char and not a pointer
> + * @from: String to copy, may be a pointer or const char array
> + *
> + * Helper for strscpy_pad.
> + * Copies a maximum of sizeof(@to) bytes of @from with %NUL termination
> + * and zero-pads the remaining size of @to
> + *
> + * Returns:
> + * * The number of characters copied (not including the trailing %NUL)
> + * * -E2BIG if @to is a zero size array.
> + */
> +#define stracpy_pad(to, from) \
> +({ \
> + size_t size = ARRAY_SIZE(to); \
> + BUILD_BUG_ON(!__same_type(typeof(*to), char)); \
> + \
> + strscpy_pad(to, from, size); \
> +})
> +
> #ifndef __HAVE_ARCH_STRCAT
> extern char * strcat(char *, const char *);
> #endif
> --
> 2.15.0
>
--
Kees Cook
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