patches/old/string-add-stracpy-and-stracpy_pad-mechanisms.patch

From: Joe Perches <joe@perches.com>
Subject: string: add stracpy and stracpy_pad mechanisms

Several uses of strlcpy and strscpy have had defects because the last
argument of each function is misused or typoed.

Add macro mechanisms to avoid this defect.

stracpy (copy a string to a string array) must have a string array as the
first argument (dest) and uses sizeof(dest) as the count of bytes to copy.

These mechanisms verify that the dest argument is an array of char or
other compatible types like u8 or s8 or equivalent.

A BUILD_BUG is emitted when the type of dest is not compatible.

Link: http://lkml.kernel.org/r/ed4611a4a96057bf8076856560bfbf9b5e95d390.1563889130.git.joe@perches.com
Signed-off-by: Joe Perches <joe@perches.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Cc: Jann Horn <jannh@google.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Nitin Gote <nitin.r.gote@intel.com>
Cc: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Cc: Stephen Kitt <steve@sk2.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/string.h |   45 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

--- a/include/linux/string.h~string-add-stracpy-and-stracpy_pad-mechanisms
+++ a/include/linux/string.h
@@ -35,6 +35,51 @@ ssize_t strscpy(char *, const char *, si
 /* Wraps calls to strscpy()/memset(), no arch specific code required */
 ssize_t strscpy_pad(char *dest, const char *src, size_t count);
 
+/**
+ * stracpy - Copy a C-string into an array of char/u8/s8 or equivalent
+ * @dest: Where to copy the string, must be an array of char and not a pointer
+ * @src: String to copy, may be a pointer or const char array
+ *
+ * Helper for strscpy().
+ * Copies a maximum of sizeof(@dest) bytes of @src with %NUL termination.
+ *
+ * Returns:
+ * * The number of characters copied (not including the trailing %NUL)
+ * * -E2BIG if @dest is a zero size array or @src was truncated.
+ */
+#define stracpy(dest, src)						\
+({									\
+	size_t count = ARRAY_SIZE(dest);				\
+	BUILD_BUG_ON(!(__same_type(dest, char[]) ||			\
+		       __same_type(dest, unsigned char[]) ||		\
+		       __same_type(dest, signed char[])));		\
+									\
+	strscpy(dest, src, count);					\
+})
+
+/**
+ * stracpy_pad - Copy a C-string into an array of char/u8/s8 with %NUL padding
+ * @dest: Where to copy the string, must be an array of char and not a pointer
+ * @src: String to copy, may be a pointer or const char array
+ *
+ * Helper for strscpy_pad().
+ * Copies a maximum of sizeof(@dest) bytes of @src with %NUL termination
+ * and zero-pads the remaining size of @dest
+ *
+ * Returns:
+ * * The number of characters copied (not including the trailing %NUL)
+ * * -E2BIG if @dest is a zero size array or @src was truncated.
+ */
+#define stracpy_pad(dest, src)						\
+({									\
+	size_t count = ARRAY_SIZE(dest);				\
+	BUILD_BUG_ON(!(__same_type(dest, char[]) ||			\
+		       __same_type(dest, unsigned char[]) ||		\
+		       __same_type(dest, signed char[])));		\
+									\
+	strscpy_pad(dest, src, count);					\
+})
+
 #ifndef __HAVE_ARCH_STRCAT
 extern char * strcat(char *, const char *);
 #endif
_