From 92b6e4fd767145d3bfc408fe036cdf63e09a9d89 Mon Sep 17 00:00:00 2001
From: Peter Elliott <pelliott@ualberta.ca>
Date: Sun, 10 Oct 2021 16:04:14 -0600
Subject: [PATCH] TaskBar+Utilities: Add logout(1) command, and call it in
 ShutdownDialog

logout kills the session that SystemServer --user was started with.
---
 Userland/Services/Taskbar/ShutdownDialog.cpp |  2 +-
 Userland/Utilities/logout.cpp                | 62 ++++++++++++++++++++
 2 files changed, 63 insertions(+), 1 deletion(-)
 create mode 100644 Userland/Utilities/logout.cpp

diff --git a/Userland/Services/Taskbar/ShutdownDialog.cpp b/Userland/Services/Taskbar/ShutdownDialog.cpp
index 35aab6c854..7d6cb8b1b7 100644
--- a/Userland/Services/Taskbar/ShutdownDialog.cpp
+++ b/Userland/Services/Taskbar/ShutdownDialog.cpp
@@ -26,7 +26,7 @@ struct Option {
 static const Vector<Option> options = {
     { "Power off computer", { "/bin/shutdown", "--now", nullptr }, true, true },
     { "Reboot", { "/bin/reboot", nullptr }, true, false },
-    { "Log out", {}, false, false },
+    { "Log out", { "/bin/logout", nullptr }, true, false },
 };
 
 Vector<char const*> ShutdownDialog::show()
diff --git a/Userland/Utilities/logout.cpp b/Userland/Utilities/logout.cpp
new file mode 100644
index 0000000000..0aedb63953
--- /dev/null
+++ b/Userland/Utilities/logout.cpp
@@ -0,0 +1,62 @@
+/*
+ * Copyright (c) 2021, Peter Elliott <pelliott@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibCore/ProcessStatisticsReader.h>
+#include <signal.h>
+
+static Core::ProcessStatistics const& get_proc(Core::AllProcessesStatistics const& stats, pid_t pid)
+{
+    for (auto& proc : stats.processes) {
+        if (proc.pid == pid)
+            return proc;
+    }
+    VERIFY_NOT_REACHED();
+}
+
+int main(int, char**)
+{
+    if (pledge("stdio proc rpath", nullptr) < 0) {
+        perror("pledge");
+        return 1;
+    }
+
+    if (unveil("/proc/all", "r") < 0) {
+        perror("unveil");
+        return 1;
+    }
+
+    if (unveil("/etc/passwd", "r") < 0) {
+        perror("unveil");
+        return 1;
+    }
+
+    unveil(nullptr, nullptr);
+
+    // logout finds the highest session up all nested sessions, and kills it.
+    auto stats = Core::ProcessStatisticsReader::get_all();
+    if (!stats.has_value()) {
+        warnln("couldn't get process statistics");
+        return 1;
+    }
+
+    pid_t sid = getsid(0);
+    while (true) {
+        pid_t parent = get_proc(stats.value(), sid).ppid;
+        pid_t parent_sid = get_proc(stats.value(), parent).sid;
+
+        if (parent_sid == 0)
+            break;
+
+        sid = parent_sid;
+    }
+
+    if (kill(-sid, SIGTERM) == -1) {
+        perror("kill(2)");
+        return 1;
+    }
+
+    return 0;
+}