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string: Redefine strscpy_pad() as a macro

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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: Andrew Morton <akpm@linux-foundation.org>
Cc:  <linux-hardening@vger.kernel.org>
Reviewed-by: Justin Stitt <justinstitt@google.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
This commit is contained in:
Kees Cook 2024-02-02 03:18:14 -08:00
parent 557f8c582a
commit f478898e0a
2 changed files with 31 additions and 36 deletions
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33
include/linux/string.h
View File

@ -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, the
* remaining bytes in the buffer will be filled with %NUL bytes.
*
* 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 *);

34
lib/string_helpers.c
View File

@ -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.