From af20a66874296f71618819ebce9d4335b195728c Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Wed, 22 Jan 2020 12:04:38 +0100
Subject: [PATCH] logind: check PolicyKit before allowing VT switch

Let's lock this down a bit. Effectively nothing much changes, since the
default PK policy will allow users on the VT to change VT. Only users
with no local VT session won't be able to switch VTs.

(cherry picked from commit 4acf0cfd2f92edb94ad48d04f1ce6c9ab4e19d55)

Resolves: #1797679
---
 src/login/logind-dbus.c                 | 16 +++++++
 src/login/logind-seat-dbus.c            | 58 ++++++++++++++++++++++++-
 src/login/logind-session-dbus.c         | 15 +++++++
 src/login/org.freedesktop.login1.policy | 10 +++++
 4 files changed, 98 insertions(+), 1 deletion(-)

diff --git a/src/login/logind-dbus.c b/src/login/logind-dbus.c
index dca7f4a30f..3f122fcbd9 100644
--- a/src/login/logind-dbus.c
+++ b/src/login/logind-dbus.c
@@ -913,6 +913,8 @@ static int method_activate_session(sd_bus_message *message, void *userdata, sd_b
         if (r < 0)
                 return r;
 
+        /* PolicyKit is done by bus_session_method_activate() */
+
         return bus_session_method_activate(message, session, error);
 }
 
@@ -944,6 +946,20 @@ static int method_activate_session_on_seat(sd_bus_message *message, void *userda
         if (session->seat != seat)
                 return sd_bus_error_setf(error, BUS_ERROR_SESSION_NOT_ON_SEAT, "Session %s not on seat %s", session_name, seat_name);
 
+        r = bus_verify_polkit_async(
+                        message,
+                        CAP_SYS_ADMIN,
+                        "org.freedesktop.login1.chvt",
+                        NULL,
+                        false,
+                        UID_INVALID,
+                        &m->polkit_registry,
+                        error);
+        if (r < 0)
+                return r;
+        if (r == 0)
+                return 1; /* Will call us back */
+
         r = session_activate(session);
         if (r < 0)
                 return r;
diff --git a/src/login/logind-seat-dbus.c b/src/login/logind-seat-dbus.c
index c4d9b067c6..2e590a8f21 100644
--- a/src/login/logind-seat-dbus.c
+++ b/src/login/logind-seat-dbus.c
@@ -174,6 +174,20 @@ static int method_activate_session(sd_bus_message *message, void *userdata, sd_b
         if (session->seat != s)
                 return sd_bus_error_setf(error, BUS_ERROR_SESSION_NOT_ON_SEAT, "Session %s not on seat %s", name, s->id);
 
+        r = bus_verify_polkit_async(
+                        message,
+                        CAP_SYS_ADMIN,
+                        "org.freedesktop.login1.chvt",
+                        NULL,
+                        false,
+                        UID_INVALID,
+                        &s->manager->polkit_registry,
+                        error);
+        if (r < 0)
+                return r;
+        if (r == 0)
+                return 1; /* Will call us back */
+
         r = session_activate(session);
         if (r < 0)
                 return r;
@@ -194,7 +208,21 @@ static int method_switch_to(sd_bus_message *message, void *userdata, sd_bus_erro
                 return r;
 
         if (to <= 0)
-                return -EINVAL;
+                return sd_bus_error_setf(error, SD_BUS_ERROR_INVALID_ARGS, "Invalid virtual terminal");
+
+        r = bus_verify_polkit_async(
+                        message,
+                        CAP_SYS_ADMIN,
+                        "org.freedesktop.login1.chvt",
+                        NULL,
+                        false,
+                        UID_INVALID,
+                        &s->manager->polkit_registry,
+                        error);
+        if (r < 0)
+                return r;
+        if (r == 0)
+                return 1; /* Will call us back */
 
         r = seat_switch_to(s, to);
         if (r < 0)
@@ -210,6 +238,20 @@ static int method_switch_to_next(sd_bus_message *message, void *userdata, sd_bus
         assert(message);
         assert(s);
 
+        r = bus_verify_polkit_async(
+                        message,
+                        CAP_SYS_ADMIN,
+                        "org.freedesktop.login1.chvt",
+                        NULL,
+                        false,
+                        UID_INVALID,
+                        &s->manager->polkit_registry,
+                        error);
+        if (r < 0)
+                return r;
+        if (r == 0)
+                return 1; /* Will call us back */
+
         r = seat_switch_to_next(s);
         if (r < 0)
                 return r;
@@ -224,6 +266,20 @@ static int method_switch_to_previous(sd_bus_message *message, void *userdata, sd
         assert(message);
         assert(s);
 
+        r = bus_verify_polkit_async(
+                        message,
+                        CAP_SYS_ADMIN,
+                        "org.freedesktop.login1.chvt",
+                        NULL,
+                        false,
+                        UID_INVALID,
+                        &s->manager->polkit_registry,
+                        error);
+        if (r < 0)
+                return r;
+        if (r == 0)
+                return 1; /* Will call us back */
+
         r = seat_switch_to_previous(s);
         if (r < 0)
                 return r;
diff --git a/src/login/logind-session-dbus.c b/src/login/logind-session-dbus.c
index 25c4981dc0..88a2d33dc8 100644
--- a/src/login/logind-session-dbus.c
+++ b/src/login/logind-session-dbus.c
@@ -13,6 +13,7 @@
 #include "logind.h"
 #include "signal-util.h"
 #include "strv.h"
+#include "user-util.h"
 #include "util.h"
 
 static int property_get_user(
@@ -182,6 +183,20 @@ int bus_session_method_activate(sd_bus_message *message, void *userdata, sd_bus_
         assert(message);
         assert(s);
 
+        r = bus_verify_polkit_async(
+                        message,
+                        CAP_SYS_ADMIN,
+                        "org.freedesktop.login1.chvt",
+                        NULL,
+                        false,
+                        UID_INVALID,
+                        &s->manager->polkit_registry,
+                        error);
+        if (r < 0)
+                return r;
+        if (r == 0)
+                return 1; /* Will call us back */
+
         r = session_activate(s);
         if (r < 0)
                 return r;
diff --git a/src/login/org.freedesktop.login1.policy b/src/login/org.freedesktop.login1.policy
index f1d1f956d3..83760e1580 100644
--- a/src/login/org.freedesktop.login1.policy
+++ b/src/login/org.freedesktop.login1.policy
@@ -357,4 +357,14 @@
                 </defaults>
         </action>
 
+        <action id="org.freedesktop.login1.chvt">
+                <description gettext-domain="systemd">Change Session</description>
+                <message gettext-domain="systemd">Authentication is required for changing the virtual terminal.</message>
+                <defaults>
+                        <allow_any>auth_admin_keep</allow_any>
+                        <allow_inactive>auth_admin_keep</allow_inactive>
+                        <allow_active>yes</allow_active>
+                </defaults>
+        </action>
+
 </policyconfig>