[v3,1/4] string: Redefine strscpy_pad() as a macro
Commit Message
In preparation for making strscpy_pad()'s 3rd argument optional, redefine
it as a macro. This also has the benefit of allowing greater FORITFY
introspection, as it couldn't see into the strscpy() nor the memset()
within strscpy_pad().
Cc: Andy Shevchenko <andy@kernel.org>
Cc: linux-hardening@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
include/linux/string.h | 33 +++++++++++++++++++++++++++++++--
lib/string_helpers.c | 34 ----------------------------------
2 files changed, 31 insertions(+), 36 deletions(-)
Comments
Hi,
On Tue, Feb 06, 2024 at 06:22:16AM -0800, Kees Cook wrote:
> In preparation for making strscpy_pad()'s 3rd argument optional, redefine
> it as a macro. This also has the benefit of allowing greater FORITFY
> introspection, as it couldn't see into the strscpy() nor the memset()
> within strscpy_pad().
>
> Cc: Andy Shevchenko <andy@kernel.org>
> Cc: linux-hardening@vger.kernel.org
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> include/linux/string.h | 33 +++++++++++++++++++++++++++++++--
> lib/string_helpers.c | 34 ----------------------------------
> 2 files changed, 31 insertions(+), 36 deletions(-)
>
> diff --git a/include/linux/string.h b/include/linux/string.h
> index ab148d8dbfc1..03f59cf7fe72 100644
> --- a/include/linux/string.h
> +++ b/include/linux/string.h
> @@ -70,8 +70,37 @@ extern char * strncpy(char *,const char *, __kernel_size_t);
> ssize_t strscpy(char *, const char *, size_t);
> #endif
>
> -/* Wraps calls to strscpy()/memset(), no arch specific code required */
> -ssize_t strscpy_pad(char *dest, const char *src, size_t count);
> +/**
> + * strscpy_pad() - Copy a C-string into a sized buffer
> + * @dest: Where to copy the string to
> + * @src: Where to copy the string from
> + * @count: Size of destination buffer
> + *
> + * Copy the string, or as much of it as fits, into the dest buffer. The
> + * behavior is undefined if the string buffers overlap. The destination
> + * buffer is always %NUL terminated, unless it's zero-sized.
> + *
> + * If the source string is shorter than the destination buffer, zeros
> + * the tail of the destination buffer.
> + *
> + * For full explanation of why you may want to consider using the
> + * 'strscpy' functions please see the function docstring for strscpy().
> + *
> + * Returns:
> + * * The number of characters copied (not including the trailing %NULs)
> + * * -E2BIG if count is 0 or @src was truncated.
> + */
> +#define strscpy_pad(dest, src, count) ({ \
> + char *__dst = (dest); \
> + const char *__src = (src); \
> + const size_t __count = (count); \
> + ssize_t __wrote; \
> + \
> + __wrote = strscpy(__dst, __src, __count); \
> + if (__wrote >= 0 && __wrote < __count) \
> + memset(__dst + __wrote + 1, 0, __count - __wrote - 1); \
> + __wrote; \
> +})
>
> #ifndef __HAVE_ARCH_STRCAT
> extern char * strcat(char *, const char *);
> diff --git a/lib/string_helpers.c b/lib/string_helpers.c
> index 7713f73e66b0..606c3099013f 100644
> --- a/lib/string_helpers.c
> +++ b/lib/string_helpers.c
> @@ -825,40 +825,6 @@ char **devm_kasprintf_strarray(struct device *dev, const char *prefix, size_t n)
> }
> EXPORT_SYMBOL_GPL(devm_kasprintf_strarray);
>
> -/**
> - * strscpy_pad() - Copy a C-string into a sized buffer
> - * @dest: Where to copy the string to
> - * @src: Where to copy the string from
> - * @count: Size of destination buffer
> - *
> - * Copy the string, or as much of it as fits, into the dest buffer. The
> - * behavior is undefined if the string buffers overlap. The destination
> - * buffer is always %NUL terminated, unless it's zero-sized.
> - *
> - * If the source string is shorter than the destination buffer, zeros
> - * the tail of the destination buffer.
> - *
> - * For full explanation of why you may want to consider using the
> - * 'strscpy' functions please see the function docstring for strscpy().
> - *
> - * Returns:
> - * * The number of characters copied (not including the trailing %NUL)
> - * * -E2BIG if count is 0 or @src was truncated.
> - */
> -ssize_t strscpy_pad(char *dest, const char *src, size_t count)
> -{
> - ssize_t written;
> -
> - written = strscpy(dest, src, count);
> - if (written < 0 || written == count - 1)
> - return written;
> -
> - memset(dest + written + 1, 0, count - written - 1);
> -
> - return written;
> -}
> -EXPORT_SYMBOL(strscpy_pad);
Yep, looks good. This is reminiscent of strtomem and strtomem_pad.
Reviewed-by: Justin Stitt <justinstitt@google.com>
> -
> /**
> * skip_spaces - Removes leading whitespace from @str.
> * @str: The string to be stripped.
> --
> 2.34.1
>
Thanks
Justin
@@ -70,8 +70,37 @@ extern char * strncpy(char *,const char *, __kernel_size_t);
ssize_t strscpy(char *, const char *, size_t);
#endif
-/* Wraps calls to strscpy()/memset(), no arch specific code required */
-ssize_t strscpy_pad(char *dest, const char *src, size_t count);
+/**
+ * strscpy_pad() - Copy a C-string into a sized buffer
+ * @dest: Where to copy the string to
+ * @src: Where to copy the string from
+ * @count: Size of destination buffer
+ *
+ * Copy the string, or as much of it as fits, into the dest buffer. The
+ * behavior is undefined if the string buffers overlap. The destination
+ * buffer is always %NUL terminated, unless it's zero-sized.
+ *
+ * If the source string is shorter than the destination buffer, zeros
+ * the tail of the destination buffer.
+ *
+ * For full explanation of why you may want to consider using the
+ * 'strscpy' functions please see the function docstring for strscpy().
+ *
+ * Returns:
+ * * The number of characters copied (not including the trailing %NULs)
+ * * -E2BIG if count is 0 or @src was truncated.
+ */
+#define strscpy_pad(dest, src, count) ({ \
+ char *__dst = (dest); \
+ const char *__src = (src); \
+ const size_t __count = (count); \
+ ssize_t __wrote; \
+ \
+ __wrote = strscpy(__dst, __src, __count); \
+ if (__wrote >= 0 && __wrote < __count) \
+ memset(__dst + __wrote + 1, 0, __count - __wrote - 1); \
+ __wrote; \
+})
#ifndef __HAVE_ARCH_STRCAT
extern char * strcat(char *, const char *);
@@ -825,40 +825,6 @@ char **devm_kasprintf_strarray(struct device *dev, const char *prefix, size_t n)
}
EXPORT_SYMBOL_GPL(devm_kasprintf_strarray);
-/**
- * strscpy_pad() - Copy a C-string into a sized buffer
- * @dest: Where to copy the string to
- * @src: Where to copy the string from
- * @count: Size of destination buffer
- *
- * Copy the string, or as much of it as fits, into the dest buffer. The
- * behavior is undefined if the string buffers overlap. The destination
- * buffer is always %NUL terminated, unless it's zero-sized.
- *
- * If the source string is shorter than the destination buffer, zeros
- * the tail of the destination buffer.
- *
- * For full explanation of why you may want to consider using the
- * 'strscpy' functions please see the function docstring for strscpy().
- *
- * Returns:
- * * The number of characters copied (not including the trailing %NUL)
- * * -E2BIG if count is 0 or @src was truncated.
- */
-ssize_t strscpy_pad(char *dest, const char *src, size_t count)
-{
- ssize_t written;
-
- written = strscpy(dest, src, count);
- if (written < 0 || written == count - 1)
- return written;
-
- memset(dest + written + 1, 0, count - written - 1);
-
- return written;
-}
-EXPORT_SYMBOL(strscpy_pad);
-
/**
* skip_spaces - Removes leading whitespace from @str.
* @str: The string to be stripped.