[spice-gtk] usb-acl-helper: Clear environment

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From: Colin Walters <walters@xxxxxxxxxx>

Otherwise we can be subject to attack via environment variables such
as DBUS_SYSTEM_BUS_ADDRESS.
This addresses CVE-2012-4425 http://seclists.org/oss-sec/2012/q3/470
---
 configure.ac                           |  2 ++
 gtk/spice-client-glib-usb-acl-helper.c | 24 +++++++++++++++++++++++-
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/configure.ac b/configure.ac
index 4a220d1..c7367cc 100644
--- a/configure.ac
+++ b/configure.ac
@@ -244,6 +244,8 @@ else
         EXTERNAL_PNP_IDS="$with_pnp_ids_path"
 fi
 
+AC_CHECK_FUNCS(clearenv)
+
 PKG_CHECK_MODULES(GLIB2, glib-2.0 >= 2.22)
 AC_SUBST(GLIB2_CFLAGS)
 AC_SUBST(GLIB2_LIBS)
diff --git a/gtk/spice-client-glib-usb-acl-helper.c b/gtk/spice-client-glib-usb-acl-helper.c
index 724d62a..93b9b3a 100644
--- a/gtk/spice-client-glib-usb-acl-helper.c
+++ b/gtk/spice-client-glib-usb-acl-helper.c
@@ -158,7 +158,8 @@ static void cleanup(void)
     if (state == STATE_WAITING_FOR_STDIN_EOF)
         set_facl(path, getuid(), 0);
 
-    g_main_loop_quit(loop);
+    if (loop)
+        g_main_loop_quit(loop);
 }
 
 /* Not available in polkit < 0.101 */
@@ -311,11 +312,32 @@ polkit_authority_get_sync (GCancellable *cancellable, GError **error)
 }
 #endif
 
+#ifndef HAVE_CLEARENV
+extern char **environ;
+
+static int
+clearenv (void)
+{
+        if (environ != NULL)
+                environ[0] = NULL;
+        return 0;
+}
+#endif
+
 int main(void)
 {
     pid_t parent_pid;
     GInputStream *stdin_unix_stream;
 
+  /* Nuke the environment to get a well-known and sanitized
+   * environment to avoid attacks via e.g. the DBUS_SYSTEM_BUS_ADDRESS
+   * environment variable and similar.
+   */
+    if (clearenv () != 0) {
+        FATAL_ERROR("Error clearing environment: %s\n", g_strerror (errno));
+        return 1;
+    }
+
     g_type_init();
 
     loop = g_main_loop_new(NULL, FALSE);
-- 
1.7.11.4

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