login: use parse_uid() when unmounting user runtime directory

When unmounting user runtime directory, only UID is necessary,
and the corresponding user may not exist anymore.
This makes first try to parse the input by parse_uid(), and only if it
fails, prase the input by get_user_creds().

Fixes #9541.

src/login/user-runtime-dir.c

@@ -111,25 +111,53 @@ static int user_remove_runtime_path(const char *runtime_path) {
         return r;
 }
 
-static int do_mount(const char *runtime_path, uid_t uid, gid_t gid) {
+static int do_mount(const char *user) {
+        char runtime_path[sizeof("/run/user") + DECIMAL_STR_MAX(uid_t)];
         size_t runtime_dir_size;
+        uid_t uid;
+        gid_t gid;
+        int r;
+
+        r = get_user_creds(&user, &uid, &gid, NULL, NULL);
+        if (r < 0)
+                return log_error_errno(r,
+                                       r == -ESRCH ? "No such user \"%s\"" :
+                                       r == -ENOMSG ? "UID \"%s\" is invalid or has an invalid main group"
+                                                    : "Failed to look up user \"%s\": %m",
+                                       user);
+
+        xsprintf(runtime_path, "/run/user/" UID_FMT, uid);
 
         assert_se(gather_configuration(&runtime_dir_size) == 0);
 
         log_debug("Will mount %s owned by "UID_FMT":"GID_FMT, runtime_path, uid, gid);
         return user_mkdir_runtime_path(runtime_path, uid, gid, runtime_dir_size);
 }
 
-static int do_umount(const char *runtime_path) {
+static int do_umount(const char *user) {
+        char runtime_path[sizeof("/run/user") + DECIMAL_STR_MAX(uid_t)];
+        uid_t uid;
+        int r;
+
+        /* The user may be already removed. So, first try to parse the string by parse_uid(),
+         * and if it fails, fallback to get_user_creds().*/
+        if (parse_uid(user, &uid) < 0) {
+                r = get_user_creds(&user, &uid, NULL, NULL, NULL);
+                if (r < 0)
+                        return log_error_errno(r,
+                                               r == -ESRCH ? "No such user \"%s\"" :
+                                               r == -ENOMSG ? "UID \"%s\" is invalid or has an invalid main group"
+                                                            : "Failed to look up user \"%s\": %m",
+                                               user);
+        }
+
+        xsprintf(runtime_path, "/run/user/" UID_FMT, uid);
+
         log_debug("Will remove %s", runtime_path);
         return user_remove_runtime_path(runtime_path);
 }
 
 int main(int argc, char *argv[]) {
-        const char *user;
-        uid_t uid;
-        gid_t gid;
-        char runtime_path[sizeof("/run/user") + DECIMAL_STR_MAX(uid_t)];
         int r;
 
         log_parse_environment();
@@ -146,23 +174,10 @@ int main(int argc, char *argv[]) {
 
         umask(0022);
 
-        user = argv[2];
-        r = get_user_creds(&user, &uid, &gid, NULL, NULL);
-        if (r < 0) {
-                log_error_errno(r,
-                                r == -ESRCH ? "No such user \"%s\"" :
-                                r == -ENOMSG ? "UID \"%s\" is invalid or has an invalid main group"
-                                             : "Failed to look up user \"%s\": %m",
-                                user);
-                return EXIT_FAILURE;
-        }
-
-        xsprintf(runtime_path, "/run/user/" UID_FMT, uid);
-
         if (streq(argv[1], "start"))
-                r = do_mount(runtime_path, uid, gid);
+                r = do_mount(argv[2]);
         else if (streq(argv[1], "stop"))
-                r = do_umount(runtime_path);
+                r = do_umount(argv[2]);
         else
                 assert_not_reached("Unknown verb!");