tools/libfsimage: Remove the XEN_FSIMAGE_FSDIR environment variable

This was reported to the security team, demonstrating that code execution
could be achieved, but without a demonstration of a priviliege boundary being
bypassed.

Still, it's a high risk path with no obvious evidence of having been used even
for debugging, so remove the environment variable and use the build time
$(libdir)/xenfsimage path only.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
Acked-by: Anthony PERARD <anthony.perard@vates.tech>
Release-Acked-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>

tools/libfsimage/common/fsimage_plugin.c

@@ -121,7 +121,7 @@ fail:
 
 int fsi_init(void)
 {
-	const char *fsdir = getenv("XEN_FSIMAGE_FSDIR");
+	const char *fsdir = FSIMAGE_FSDIR;
 	struct dirent *dp = NULL;
 	DIR *dir = NULL;
 	char *tmp = NULL;
@@ -129,9 +129,6 @@ int fsi_init(void)
 	int err;
 	int ret = -1;
 
-	if (fsdir == NULL)
-		fsdir = FSIMAGE_FSDIR;
-
 	if ((name_max = pathconf(fsdir, _PC_NAME_MAX)) == -1)
 		goto fail;