fbdev/vt8623fb: Duplicate video-mode option string

Assume that the driver does not own the option string or its substrings
and hence duplicate the option string for the video mode. The driver only
parses the option string once as part of module initialization, so use
a static buffer to store the duplicated mode option. Linux automatically
frees the memory upon releasing the module.

Done in preparation of constifying the option string.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>

drivers/video/fbdev/vt8623fb.c

@@ -929,8 +929,17 @@ static int __init vt8623fb_init(void)
 	if (fb_get_options("vt8623fb", &option))
 		return -ENODEV;
 
-	if (option && *option)
-		mode_option = option;
+	if (option && *option) {
+		static char mode_option_buf[256];
+		int ret;
+
+		ret = snprintf(mode_option_buf, sizeof(mode_option_buf), "%s", option);
+		if (WARN(ret < 0, "vt8623fb: ignoring invalid option, ret=%d\n", ret))
+			break;
+		if (WARN(ret >= sizeof(mode_option_buf), "vt8623fb: option too long\n"))
+			break;
+		mode_option = mode_option_buf;
+	}
 #endif
 
 	pr_debug("vt8623fb: initializing\n");