Warn loudly if somebody passes a negative value as

the size to "vsnprintf()".

That's a pretty clear case of overflow.

lib/vsprintf.c

@@ -254,6 +254,15 @@ int vsnprintf(char *buf, size_t size, const char *fmt, va_list args)
 				/* 'z' support added 23/7/1999 S.H.    */
 				/* 'z' changed to 'Z' --davidm 1/25/99 */
 
+	/* Reject out-of-range values early */
+	if (unlikely((int) size < 0)) {
+		/* There can be only one.. */
+		static int warn = 1;
+		WARN_ON(warn);
+		warn = 0;
+		return 0;
+	}
+
 	str = buf;
 	end = buf + size - 1;
 
@@ -498,7 +507,7 @@ EXPORT_SYMBOL(snprintf);
  */
 int vsprintf(char *buf, const char *fmt, va_list args)
 {
-	return vsnprintf(buf, 0xFFFFFFFFUL, fmt, args);
+	return vsnprintf(buf, (~0U)>>1, fmt, args);
 }
 
 EXPORT_SYMBOL(vsprintf);