From c32c06e814586431c4604461bf467f0ff73f909b Mon Sep 17 00:00:00 2001
From: Philip Withnall <philip.withnall@collabora.co.uk>
Date: Tue, 2 Jun 2015 16:19:51 +0100
Subject: [PATCH] sessionmonitor-systemd: Use sd_uid_get_state() to check
 session activity
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Instead of using sd_pid_get_session() then sd_session_is_active() to
determine whether the user is active, use sd_uid_get_state() directly.
This gets the maximum of the states of all the user’s sessions, rather
than the state of the session containing the subject process. Since the
user is the security boundary, this is fine.

This change is necessary for `systemd --user` sessions, where most user
code will be forked off user@.service, rather than running inside the
logind session (whether that be a foreground/active or background/online
session).

Policy-wise, the change is from checking whether the subject process is
in an active session; to checking whether the subject process is owned
by a user with at least one active session.

https://bugs.freedesktop.org/show_bug.cgi?id=76358
---
 .../polkitbackendsessionmonitor-systemd.c          | 33 +++++++++++++++++++++-
 1 file changed, 32 insertions(+), 1 deletion(-)

diff --git a/src/polkitbackend/polkitbackendsessionmonitor-systemd.c b/src/polkitbackend/polkitbackendsessionmonitor-systemd.c
index 9995f87..2a6c739 100644
--- a/src/polkitbackend/polkitbackendsessionmonitor-systemd.c
+++ b/src/polkitbackend/polkitbackendsessionmonitor-systemd.c
@@ -389,6 +389,37 @@ gboolean
 polkit_backend_session_monitor_is_session_active (PolkitBackendSessionMonitor *monitor,
                                                   PolkitSubject               *session)
 {
-  return sd_session_is_active (polkit_unix_session_get_session_id (POLKIT_UNIX_SESSION (session)));
+  const char *session_id;
+  char *state;
+  uid_t uid;
+  gboolean is_active = FALSE;
+
+  session_id = polkit_unix_session_get_session_id (POLKIT_UNIX_SESSION (session));
+
+  g_debug ("Checking whether session %s is active.", session_id);
+
+  /* Check whether *any* of the user's current sessions are active. */
+  if (sd_session_get_uid (session_id, &uid) < 0)
+    goto fallback;
+
+  g_debug ("Session %s has UID %u.", session_id, uid);
+
+  if (sd_uid_get_state (uid, &state) < 0)
+    goto fallback;
+
+  g_debug ("UID %u has state %s.", uid, state);
+
+  is_active = (g_strcmp0 (state, "active") == 0);
+  free (state);
+
+  return is_active;
+
+fallback:
+  /* Fall back to checking the session. This is not ideal, since the user
+   * might have multiple sessions, and we cannot guarantee to have chosen
+   * the active one.
+   *
+   * See: https://bugs.freedesktop.org/show_bug.cgi?id=76358. */
+  return sd_session_is_active (session_id);
 }
 
-- 
2.1.0