string: Allow 2-argument strscpy_pad()

Similar to strscpy(), update strscpy_pad()'s 3rd argument to be
optional when the destination is a compile-time known size array.

Cc: Andy Shevchenko <andy@kernel.org>
Cc:  <linux-hardening@vger.kernel.org>
Reviewed-by: Justin Stitt <justinstitt@google.com>
Signed-off-by: Kees Cook <keescook@chromium.org>

diff --git a/include/linux/string.h b/include/linux/string.h
index 0d66bf9407fdd4f71812e8cfe8358a3e0453e6a1..96e6b1af86b5aa47ce8c0a0833b39213119577bc 100644 (file)
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -77,6 +77,10 @@ ssize_t sized_strscpy(char *, const char *, size_t);
        sized_strscpy(dst, src, sizeof(dst) + __must_be_array(dst))
 #define __strscpy1(dst, src, size)     sized_strscpy(dst, src, size)
 
+#define __strscpy_pad0(dst, src, ...)  \
+       sized_strscpy_pad(dst, src, sizeof(dst) + __must_be_array(dst))
+#define __strscpy_pad1(dst, src, size) sized_strscpy_pad(dst, src, size)
+
 /**
  * strscpy - Copy a C-string into a sized buffer
  * @dst: Where to copy the string to
@@ -102,11 +106,23 @@ ssize_t sized_strscpy(char *, const char *, size_t);
 #define strscpy(dst, src, ...) \
        CONCATENATE(__strscpy, COUNT_ARGS(__VA_ARGS__))(dst, src, __VA_ARGS__)
 
+#define sized_strscpy_pad(dest, src, count)    ({                      \
+       char *__dst = (dest);                                           \
+       const char *__src = (src);                                      \
+       const size_t __count = (count);                                 \
+       ssize_t __wrote;                                                \
+                                                                       \
+       __wrote = sized_strscpy(__dst, __src, __count);                 \
+       if (__wrote >= 0 && __wrote < __count)                          \
+               memset(__dst + __wrote + 1, 0, __count - __wrote - 1);  \
+       __wrote;                                                        \
+})
+
 /**
  * strscpy_pad() - Copy a C-string into a sized buffer
- * @dest: Where to copy the string to
+ * @dst: Where to copy the string to
  * @src: Where to copy the string from
- * @count: Size of destination buffer
+ * @...: 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
@@ -122,17 +138,8 @@ ssize_t sized_strscpy(char *, const char *, size_t);
  * * 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;                                                        \
-})
+#define strscpy_pad(dst, src, ...)     \
+       CONCATENATE(__strscpy_pad, COUNT_ARGS(__VA_ARGS__))(dst, src, __VA_ARGS__)
 
 #ifndef __HAVE_ARCH_STRCAT
 extern char * strcat(char *, const char *);