From b9f4200b9674638ee2879db568e30219e81d5ed8 Mon Sep 17 00:00:00 2001
From: Michael Catanzaro <mcatanzaro@redhat.com>
Date: Thu, 12 May 2022 12:44:59 -0500
Subject: [PATCH 1/2] Bind gssproxy socket into sandbox environment

We're using a directory rather than binding a socket directly for
increased robustness. In theory, if gssproxy crashes on the host, a new
socket that a new gssproxy process creates should be immediately visible
inside the sandbox. Nifty.

Previously, applications that wanted to use Kerberos authentication
would have to punch a sandbox hole for the host's KCM socket. In
contrast, this gssproxy socket is designed for use by sandboxed apps.

See also: https://github.com/gssapi/gssproxy/issues/45
---
 common/flatpak-run.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/common/flatpak-run.c b/common/flatpak-run.c
index bf85f47c..3ec007cf 100644
--- a/common/flatpak-run.c
+++ b/common/flatpak-run.c
@@ -955,6 +955,19 @@ flatpak_run_add_pulseaudio_args (FlatpakBwrap         *bwrap,
     flatpak_bwrap_add_args (bwrap, "--dev-bind", "/dev/snd", "/dev/snd", NULL);
 }
 
+static void
+flatpak_run_add_gssproxy_args (FlatpakBwrap *bwrap)
+{
+  /* We only expose the gssproxy user service. The gssproxy system service is
+   * not intended to be exposed to sandboxed environments.
+   */
+  g_autofree char *gssproxy_host_dir = g_build_filename (g_get_user_runtime_dir (), "gssproxy", NULL);
+  const char *gssproxy_sandboxed_dir = "/run/flatpak/gssproxy/";
+
+  if (g_file_test (gssproxy_host_dir, G_FILE_TEST_EXISTS))
+    flatpak_bwrap_add_args (bwrap, "--ro-bind", gssproxy_host_dir, gssproxy_sandboxed_dir, NULL);
+}
+
 static void
 flatpak_run_add_resolved_args (FlatpakBwrap *bwrap)
 {
@@ -4611,7 +4624,10 @@ flatpak_run_app (FlatpakDecomposed *app_ref,
     }
 
   if ((app_context->shares & FLATPAK_CONTEXT_SHARED_NETWORK) != 0)
-    flatpak_run_add_resolved_args (bwrap);
+    {
+      flatpak_run_add_gssproxy_args (bwrap);
+      flatpak_run_add_resolved_args (bwrap);
+    }
 
   flatpak_run_add_journal_args (bwrap);
   add_font_path_args (bwrap);
-- 
2.37.3

From 9e32923a46ffd336dffc4fa7c7a1ee05ae2d39ae Mon Sep 17 00:00:00 2001
From: Michael Catanzaro <mcatanzaro@redhat.com>
Date: Mon, 23 May 2022 09:59:48 -0500
Subject: [PATCH 2/2] Block KRB5CCNAME from inheriting into sandbox

If this environment variable is set on the host, it's going to mess up
authentication in the sandbox. For example, if the host has:

KRB5CCNAME=KCM:

then the sandboxed process will try to use the host KCM socket, which is
not available in the sandboxed environment, rather than the gssproxy
socket that we want it to use. We need to unset it to ensure that
whatever configuration we ship in the runtime gets used instead. We have
switched the GNOME runtime to use an empty krb5.conf and it works as
long as we don't break it with this environment variable meant for the
host.
---
 common/flatpak-run.c | 4 +++-
 doc/flatpak-run.xml  | 1 +
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/common/flatpak-run.c b/common/flatpak-run.c
index 3ec007cf..b650be46 100644
--- a/common/flatpak-run.c
+++ b/common/flatpak-run.c
@@ -1887,7 +1887,8 @@ static const ExportData default_exports[] = {
   {"XDG_RUNTIME_DIR", NULL},
 
   /* Some env vars are common enough and will affect the sandbox badly
-     if set on the host. We clear these always. */
+     if set on the host. We clear these always. If updating this list,
+     also update the list in flatpak-run.xml. */
   {"PYTHONPATH", NULL},
   {"PERLLIB", NULL},
   {"PERL5LIB", NULL},
@@ -1904,6 +1905,7 @@ static const ExportData default_exports[] = {
   {"GST_PTP_HELPER", NULL},
   {"GST_PTP_HELPER_1_0", NULL},
   {"GST_INSTALL_PLUGINS_HELPER", NULL},
+  {"KRB5CCNAME", NULL},
 };
 
 static const ExportData no_ld_so_cache_exports[] = {
diff --git a/doc/flatpak-run.xml b/doc/flatpak-run.xml
index e1aa5e1c..77cd3ad0 100644
--- a/doc/flatpak-run.xml
+++ b/doc/flatpak-run.xml
@@ -97,6 +97,7 @@
             <member>PERLLIB</member>
             <member>PERL5LIB</member>
             <member>XCURSOR_PATH</member>
+            <member>KRB5CCNAME</member>
         </simplelist>
         <para>
             Also several environment variables with the prefix "GST_" that are used by gstreamer
-- 
2.37.3