sysext: Check if preexisting mutable directory has a valid mode

Preexisting mutable directory is likely set by the admin, so we expect it to be
set up properly instead of changing the mode of the directory behind admin's
back.

1 files changed, 39 insertions, 1 deletions

diff --git a/src/sysext/sysext.c b/src/sysext/sysext.c
index 07a9619bd1..47ba78ab3a 100644
--- a/src/sysext/sysext.c
+++ b/src/sysext/sysext.c
@@ -768,8 +768,37 @@ static int resolve_hierarchy(const char *hierarchy, char **ret_resolved_hierarch
         return 0;
 }
 
+static int mutable_directory_mode_matches_hierarchy(
+                const char *root_or_null,
+                const char *path,
+                mode_t hierarchy_mode) {
+
+        _cleanup_free_ char *path_in_root = NULL;
+        struct stat st;
+        mode_t actual_mode;
+
+        assert(path);
+
+        path_in_root = path_join(root_or_null, path);
+        if (!path_in_root)
+                return log_oom();
+
+        if (stat(path_in_root, &st) < 0) {
+                if (errno == ENOENT)
+                        return 0;
+                return log_error_errno(errno, "Failed to stat mutable directory '%s': %m", path_in_root);
+        }
+
+        actual_mode = st.st_mode & 0777;
+        if (actual_mode != hierarchy_mode)
+                return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Mutable directory '%s' has mode %04o, ought to have mode %04o", path_in_root, actual_mode, hierarchy_mode);
+
+        return 0;
+}
+
 static int resolve_mutable_directory(
                 const char *hierarchy,
+                mode_t hierarchy_mode,
                 const char *workspace,
                 char **ret_resolved_mutable_directory) {
 
@@ -801,6 +830,15 @@ static int resolve_mutable_directory(
         if (!path)
                 return log_oom();
 
+        if (IN_SET(arg_mutable, MUTABLE_YES, MUTABLE_AUTO)) {
+                /* If there already is a mutable directory, check if its mode matches hierarchy. Merged
+                 * hierarchy will have the same mode as the mutable directory, so we want no surprising mode
+                 * changes here. */
+                r = mutable_directory_mode_matches_hierarchy(root, path, hierarchy_mode);
+                if (r < 0)
+                        return r;
+        }
+
         if (IN_SET(arg_mutable, MUTABLE_YES, MUTABLE_EPHEMERAL, MUTABLE_EPHEMERAL_IMPORT)) {
                 _cleanup_free_ char *path_in_root = NULL;
 
@@ -847,7 +885,7 @@ static int overlayfs_paths_new(const char *hierarchy, const char *workspace_path
         } else
                 hierarchy_mode = 0755;
 
-        r = resolve_mutable_directory(hierarchy, workspace_path, &resolved_mutable_directory);
+        r = resolve_mutable_directory(hierarchy, hierarchy_mode, workspace_path, &resolved_mutable_directory);
         if (r < 0)
                 return r;