From 33f835ec7c74629d4a6982c3b75630af2cd5d65b Mon Sep 17 00:00:00 2001
From: Simon McVittie <simon.mcvittie@collabora.co.uk>
Date: Wed, 17 Jun 2015 16:45:49 +0100
Subject: [PATCH] logind: save /run/systemd/users/UID before starting
user@.service
Previously, this had a race condition during a user's first login.
Some component calls CreateSession (most likely by a PAM service
other than 'systemd-user' running pam_systemd), with the following
results:
- logind:
* create the user's XDG_RUNTIME_DIR
* tell pid 1 to create user-UID.slice
* tell pid 1 to start user@UID.service
Then these two processes race:
- logind:
* save information including XDG_RUNTIME_DIR to /run/systemd/users/UID
- the subprocess of pid 1 responsible for user@service:
* start a 'systemd-user' PAM session, which reads XDG_RUNTIME_DIR
and puts it in the environment
* run systemd --user, which requires XDG_RUNTIME_DIR in the
environment
If logind wins the race, which usually happens, everything is fine;
but if the subprocesses of pid 1 win the race, which can happen
under load, then systemd --user exits unsuccessfully.
To avoid this race, we have to write out /run/systemd/users/UID
even though the service has not "officially" started yet;
previously this did an early-return without saving anything.
Record its state as OPENING in this case.
Bug: https://github.com/systemd/systemd/issues/232
Reviewed-by: Philip Withnall <philip.withnall@collabora.co.uk>
(cherry picked from commit 71161305f191d1fe1242ccca47657f9ab51caad4)
---
src/login/logind-user.c | 22 +++++++++++++++++-----
1 file changed, 17 insertions(+), 5 deletions(-)
diff --git a/src/login/logind-user.c b/src/login/logind-user.c
index f4c4490e8f..21acf2afe3 100644
--- a/src/login/logind-user.c
+++ b/src/login/logind-user.c
@@ -104,7 +104,7 @@ void user_free(User *u) {
free(u);
}
-int user_save(User *u) {
+static int user_save_internal(User *u) {
_cleanup_free_ char *temp_path = NULL;
_cleanup_fclose_ FILE *f = NULL;
int r;
@@ -112,9 +112,6 @@ int user_save(User *u) {
assert(u);
assert(u->state_file);
- if (!u->started)
- return 0;
-
r = mkdir_safe_label("/run/systemd/users", 0755, 0, 0);
if (r < 0)
goto finish;
@@ -257,6 +254,15 @@ finish:
return r;
}
+int user_save(User *u) {
+ assert(u);
+
+ if (!u->started)
+ return 0;
+
+ return user_save_internal (u);
+}
+
int user_load(User *u) {
_cleanup_free_ char *display = NULL, *realtime = NULL, *monotonic = NULL;
Session *s = NULL;
@@ -452,6 +458,12 @@ int user_start(User *u) {
if (r < 0)
return r;
+ /* Save the user data so far, because pam_systemd will read the
+ * XDG_RUNTIME_DIR out of it while starting up systemd --user.
+ * We need to do user_save_internal() because we have not
+ * "officially" started yet. */
+ user_save_internal(u);
+
/* Spawn user systemd */
r = user_start_service(u);
if (r < 0)
@@ -703,7 +715,7 @@ UserState user_get_state(User *u) {
if (u->stopping)
return USER_CLOSING;
- if (u->slice_job || u->service_job)
+ if (!u->started || u->slice_job || u->service_job)
return USER_OPENING;
if (u->sessions) {