basic: fix touch() creating files with 07777 mode

mode_t is unsigned, so MODE_INVALID < 0 can never be true.

This fixes a possible DoS where any user could fill /run by writing to
a world-writable /run/elogind/show-status.

diff --git a/src/basic/fs-util.c b/src/basic/fs-util.c
index b13a9cbea7ca725d27b7b79de02aeaa7f73d3418..e895cac4f8573ea82a5971a9e30c4eeda87ea60a 100644 (file)
--- a/src/basic/fs-util.c
+++ b/src/basic/fs-util.c
@@ -333,7 +333,8 @@ int touch_file(const char *path, bool parents, usec_t stamp, uid_t uid, gid_t gi
         if (parents)
                 mkdir_parents(path, 0755);
 
-        fd = open(path, O_WRONLY|O_CREAT|O_CLOEXEC|O_NOCTTY, mode > 0 ? mode : 0644);
+        fd = open(path, O_WRONLY|O_CREAT|O_CLOEXEC|O_NOCTTY,
+                        (mode == 0 || mode == MODE_INVALID) ? 0644 : mode);
         if (fd < 0)
                 return -errno;