[PATCH v2 2/2] tools: include: add proper strscpy() declaration

[Lucas Poupeau]

Currently, strscpy() is defined as a macro for strcpy() in the tools
headers. This is unsafe and prevents using the real strscpy() logic
that provides better buffer overflow protection.

Remove the macro hack and add a proper extern declaration for
strscpy(). This allows tools to use the safer string copying API
once the implementation is provided.

Suggested-by: Maxwell Doose <m32285159@xxxxxxxxx>
Signed-off-by: Lucas Poupeau <lucasp.linux@xxxxxxxxx>
---
 tools/include/linux/string.h |  5 ++++-
 tools/lib/string.c           | 37 ++++++++++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/tools/include/linux/string.h b/tools/include/linux/string.h
index 51ad3cf4fa82..4f3547d0cd84 100644
--- a/tools/include/linux/string.h
+++ b/tools/include/linux/string.h
@@ -12,7 +12,6 @@ void argv_free(char **argv);
 
 int strtobool(const char *s, bool *res);
 
-#define strscpy strcpy
 
 /*
  * glibc based builds needs the extern while uClibc doesn't.
@@ -30,6 +29,10 @@ extern size_t strlcpy(char *dest, const char *src, size_t size);
 #endif
 #endif
 
+extern ssize_t strscpy(char *dest, const char *src, size_t count);
+
+char *str_error_r(int errnum, char *buf, size_t buflen);
+
 char *str_error_r(int errnum, char *buf, size_t buflen);
 
 char *strreplace(char *s, char old, char new);
diff --git a/tools/lib/string.c b/tools/lib/string.c
index 3126d2cff716..12fabbe583cf 100644
--- a/tools/lib/string.c
+++ b/tools/lib/string.c
@@ -36,6 +36,43 @@ void *memdup(const void *src, size_t len)
 	return p;
 }
 
+/**
+ * strscpy - 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 source string to the destination buffer. The result is
+ * always a valid NUL-terminated string that fits in the buffer.
+ *
+ * Return:
+ * * The number of characters copied (not including the trailing NUL)
+ * * -E2BIG if count is 0 or @src was truncated.
+ */
+ssize_t strscpy(char *dest, const char *src, size_t count)
+{
+	size_t res = 0;
+
+	if (count == 0)
+		return -E2BIG;
+
+	while (count) {
+		char c = src[res];
+
+		dest[res] = c;
+		if (!c)
+			return res;
+		res++;
+		count--;
+	}
+
+	/* Hit buffer length without finding a NUL; force NUL-termination. */
+	if (res)
+		dest[res-1] = '\0';
+
+	return -E2BIG;
+}
+
 /**
  * strtobool - convert common user inputs into boolean values
  * @s: input string
-- 
2.54.0