smb: Annotate struct xattr_smb_acl with __counted_by()

Add the __counted_by compiler attribute to the flexible array member
entries to improve access bounds-checking via CONFIG_UBSAN_BOUNDS and
CONFIG_FORTIFY_SOURCE.
Signed-off-by: Thorsten Blum <thorsten.blum@toblux.com>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/smb/server/xattr.h

@@ -76,7 +76,7 @@ struct xattr_acl_entry {
 struct xattr_smb_acl {
 	int count;
 	int next;
-	struct xattr_acl_entry entries[];
+	struct xattr_acl_entry entries[] __counted_by(count);
 };
 
 /* 64bytes hash in xattr_ntacl is computed with sha256 */