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Commit 2a368703 authored by Tobin C. Harding's avatar Tobin C. Harding Committed by Greg Kroah-Hartman
Browse files

lib/string: Add strscpy_pad() function 



[ Upstream commit 458a3bf82df4fe1f951d0f52b1e0c1e9d5a88a3b ]

We have a function to copy strings safely and we have a function to copy
strings and zero the tail of the destination (if source string is
shorter than destination buffer) but we do not have a function to do
both at once.  This means developers must write this themselves if they
desire this functionality.  This is a chore, and also leaves us open to
off by one errors unnecessarily.

Add a function that calls strscpy() then memset()s the tail to zero if
the source string is shorter than the destination buffer.

Acked-by: default avatarKees Cook <keescook@chromium.org>
Signed-off-by: default avatarTobin C. Harding <tobin@kernel.org>
Signed-off-by: default avatarShuah Khan <shuah@kernel.org>
Signed-off-by: default avatarSasha Levin <sashal@kernel.org>
parent 9848962b

include/linux/string.h

+4 −0
Original line number Diff line number Diff line
@@ -31,6 +31,10 @@ size_t strlcpy(char *, const char *, size_t); 
#ifndef __HAVE_ARCH_STRSCPY

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);



#ifndef __HAVE_ARCH_STRCAT

extern char * strcat(char *, const char *);

#endif

lib/string.c

+40 −7
Original line number Diff line number Diff line
@@ -158,11 +158,9 @@ EXPORT_SYMBOL(strlcpy); 
 * @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 routine returns the number of characters copied (not including

 * the trailing NUL) or -E2BIG if the destination buffer wasn't big enough.

 * The behavior is undefined if the string buffers overlap.

 * The destination buffer is always NUL terminated, unless it's zero-sized.

 * 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.

 *

 * Preferred to strlcpy() since the API doesn't require reading memory

 * from the src string beyond the specified "count" bytes, and since
@@ -172,8 +170,10 @@ EXPORT_SYMBOL(strlcpy); 
 *

 * Preferred to strncpy() since it always returns a valid string, and

 * doesn't unnecessarily force the tail of the destination buffer to be

 * zeroed.  If the zeroing is desired, it's likely cleaner to use strscpy()

 * with an overflow test, then just memset() the tail of the dest buffer.

 * zeroed.  If zeroing is desired please use strscpy_pad().

 *

 * Return: The number of characters copied (not including the trailing

 *         %NUL) or -E2BIG if the destination buffer wasn't big enough.

 */

ssize_t strscpy(char *dest, const char *src, size_t count)

{
@@ -260,6 +260,39 @@ char *stpcpy(char *__restrict__ dest, const char *__restrict__ src) 
}

EXPORT_SYMBOL(stpcpy);



/**

 * 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().

 *

 * Return: The number of characters copied (not including the trailing

 *         %NUL) or -E2BIG if the destination buffer wasn't big enough.

 */

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);



#ifndef __HAVE_ARCH_STRCAT

/**

 * strcat - Append one %NUL-terminated string to another