linux-kernel - [PATCH v2 3/4] string: Allow 2-argument strscpy

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Message-Id: <20240205123525.1379299-3-keescook@chromium.org>
Date: Mon,  5 Feb 2024 04:35:23 -0800
From: Kees Cook <keescook@...omium.org>
To: Andy Shevchenko <andy@...nel.org>
Cc: Kees Cook <keescook@...omium.org>,
	linux-hardening@...r.kernel.org,
	Richard Weinberger <richard@....at>,
	Justin Stitt <justinstitt@...gle.com>,
	Anton Ivanov <anton.ivanov@...bridgegreys.com>,
	Johannes Berg <johannes@...solutions.net>,
	Willem de Bruijn <willemdebruijn.kernel@...il.com>,
	Jason Wang <jasowang@...hat.com>,
	kernel test robot <lkp@...el.com>,
	Nathan Chancellor <nathan@...nel.org>,
	Azeem Shaikh <azeemshaikh38@...il.com>,
	linux-kernel@...r.kernel.org,
	linux-um@...ts.infradead.org
Subject: [PATCH v2 3/4] 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@...nel.org>
Cc: linux-hardening@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 include/linux/string.h | 29 ++++++++++++++++++-----------
 1 file changed, 18 insertions(+), 11 deletions(-)

diff --git a/include/linux/string.h b/include/linux/string.h
index a21371aa2fd6..4f0f27013418 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -78,6 +78,10 @@ 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
@@ -103,6 +107,18 @@ 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
@@ -123,17 +139,8 @@ 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 *);
-- 
2.34.1