basic/fs-util: add a version of chmod_and_chown that doesn not use /proc

src/basic/fs-util.c

@@ -272,6 +272,52 @@ int fchmod_and_chown(int fd, mode_t mode, uid_t uid, gid_t gid) {
         return do_chown || do_chmod;
 }
 
+int chmod_and_chown_unsafe(const char *path, mode_t mode, uid_t uid, gid_t gid) {
+        bool do_chown, do_chmod;
+        struct stat st;
+
+        assert(path);
+
+        /* Change ownership and access mode of the specified path, see description of fchmod_and_chown().
+         * Should only be used on trusted paths. */
+
+        if (lstat(path, &st) < 0)
+                return -errno;
+
+        do_chown =
+                (uid != UID_INVALID && st.st_uid != uid) ||
+                (gid != GID_INVALID && st.st_gid != gid);
+
+        do_chmod =
+                !S_ISLNK(st.st_mode) && /* chmod is not defined on symlinks */
+                ((mode != MODE_INVALID && ((st.st_mode ^ mode) & 07777) != 0) ||
+                 do_chown); /* If we change ownership, make sure we reset the mode afterwards, since chown()
+                             * modifies the access mode too */
+
+        if (mode == MODE_INVALID)
+                mode = st.st_mode; /* If we only shall do a chown(), save original mode, since chown() might break it. */
+        else if ((mode & S_IFMT) != 0 && ((mode ^ st.st_mode) & S_IFMT) != 0)
+                return -EINVAL; /* insist on the right file type if it was specified */
+
+        if (do_chown && do_chmod) {
+                mode_t minimal = st.st_mode & mode; /* the subset of the old and the new mask */
+
+                if (((minimal ^ st.st_mode) & 07777) != 0)
+                        if (chmod(path, minimal & 07777) < 0)
+                                return -errno;
+        }
+
+        if (do_chown)
+                if (lchown(path, uid, gid) < 0)
+                        return -errno;
+
+        if (do_chmod)
+                if (chmod(path, mode & 07777) < 0)
+                        return -errno;
+
+        return do_chown || do_chmod;
+}
+
 int fchmod_umask(int fd, mode_t m) {
         mode_t u;
         int r;