Add support for using 3-arg pkcheck syntax for process (CVE-2013-4311)

With the existing pkcheck (pid, start time) tuple for identifying
the process, there is a race condition, where a process can make
a libvirt RPC call and in another thread exec a setuid application,
causing it to change to effective UID 0. This in turn causes polkit
to do its permission check based on the wrong UID.

To address this, libvirt must get the UID the caller had at time
of connect() (from SO_PEERCRED) and pass a (pid, start time, uid)
triple to the pkcheck program.

This fix requires that libvirt is re-built against a version of
polkit that has the fix for its CVE-2013-4288, so that libvirt
can see 'pkg-config --variable pkcheck_supports_uid polkit-gobject-1'
Signed-off-by: NColin Walters <walters@redhat.com>
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

configure.ac

@@ -1257,6 +1257,14 @@ if test "x$with_polkit" = "xyes" || test "x$with_polkit" = "xcheck"; then
   AC_PATH_PROG([PKCHECK_PATH],[pkcheck], [], [/usr/sbin:$PATH])
   if test "x$PKCHECK_PATH" != "x" ; then
     AC_DEFINE_UNQUOTED([PKCHECK_PATH],["$PKCHECK_PATH"],[Location of pkcheck program])
+    AC_MSG_CHECKING([whether pkcheck supports uid value])
+    pkcheck_supports_uid=`$PKG_CONFIG --variable pkcheck_supports_uid polkit-gobject-1`
+    if test "x$pkcheck_supports_uid" = "xtrue"; then
+      AC_MSG_RESULT([yes])
+      AC_DEFINE_UNQUOTED([PKCHECK_SUPPORTS_UID], 1, [Pass uid to pkcheck])
+    else
+      AC_MSG_RESULT([no])
+    fi
     AC_DEFINE_UNQUOTED([WITH_POLKIT], 1,
         [use PolicyKit for UNIX socket access checks])
     AC_DEFINE_UNQUOTED([WITH_POLKIT1], 1,

daemon/remote.c

@@ -2738,10 +2738,12 @@ remoteDispatchAuthPolkit(virNetServerPtr server ATTRIBUTE_UNUSED,
     int status = -1;
     char *ident = NULL;
     bool authdismissed = 0;
+    bool supportsuid = false;
     char *pkout = NULL;
     struct daemonClientPrivate *priv =
         virNetServerClientGetPrivateData(client);
     virCommandPtr cmd = NULL;
+    static bool polkitInsecureWarned;
 
     virMutexLock(&priv->lock);
     action = virNetServerClientGetReadonly(client) ?
@@ -2763,14 +2765,28 @@ remoteDispatchAuthPolkit(virNetServerPtr server ATTRIBUTE_UNUSED,
         goto authfail;
     }
 
+    if (timestamp == 0) {
+        VIR_WARN("Failing polkit auth due to missing client (pid=%lld) start time",
+                 (long long)callerPid);
+        goto authfail;
+    }
+
     VIR_INFO("Checking PID %lld running as %d",
              (long long) callerPid, callerUid);
 
     virCommandAddArg(cmd, "--process");
-    if (timestamp != 0) {
-        virCommandAddArgFormat(cmd, "%lld,%llu", (long long) callerPid, timestamp);
+# ifdef PKCHECK_SUPPORTS_UID
+    supportsuid = true;
+# endif
+    if (supportsuid) {
+        virCommandAddArgFormat(cmd, "%lld,%llu,%lu",
+                               (long long) callerPid, timestamp, (unsigned long) callerUid);
     } else {
-        virCommandAddArgFormat(cmd, "%lld", (long long) callerPid);
+        if (!polkitInsecureWarned) {
+            VIR_WARN("No support for caller UID with pkcheck. This deployment is known to be insecure.");
+            polkitInsecureWarned = true;
+        }
+        virCommandAddArgFormat(cmd, "%lld,%llu", (long long) callerPid, timestamp);
     }
     virCommandAddArg(cmd, "--allow-user-interaction");
 

libvirt.spec.in

@@ -509,8 +509,7 @@ BuildRequires: cyrus-sasl-devel
 %endif
 %if %{with_polkit}
     %if 0%{?fedora} >= 12 || 0%{?rhel} >= 6
-# Only need the binary, not -devel
-BuildRequires: polkit >= 0.93
+BuildRequires: polkit-devel >= 0.93
     %else
 BuildRequires: PolicyKit-devel >= 0.6
     %endif

src/access/viraccessdriverpolkit.c

@@ -72,8 +72,12 @@ static char *
 virAccessDriverPolkitFormatProcess(const char *actionid)
 {
     virIdentityPtr identity = virIdentityGetCurrent();
-    const char *process = NULL;
+    const char *callerPid = NULL;
+    const char *callerTime = NULL;
+    const char *callerUid = NULL;
     char *ret = NULL;
+    bool supportsuid = false;
+    static bool polkitInsecureWarned;
 
     if (!identity) {
         virAccessError(VIR_ERR_ACCESS_DENIED,
@@ -81,17 +85,43 @@ virAccessDriverPolkitFormatProcess(const char *actionid)
                        actionid);
         return NULL;
     }
-    if (virIdentityGetAttr(identity, VIR_IDENTITY_ATTR_UNIX_PROCESS_ID, &process) < 0)
+    if (virIdentityGetAttr(identity, VIR_IDENTITY_ATTR_UNIX_PROCESS_ID, &callerPid) < 0)
+        goto cleanup;
+    if (virIdentityGetAttr(identity, VIR_IDENTITY_ATTR_UNIX_PROCESS_TIME, &callerTime) < 0)
+        goto cleanup;
+    if (virIdentityGetAttr(identity, VIR_IDENTITY_ATTR_UNIX_USER_ID, &callerUid) < 0)
         goto cleanup;
 
-    if (!process) {
+    if (!callerPid) {
         virAccessError(VIR_ERR_INTERNAL_ERROR, "%s",
                        _("No UNIX process ID available"));
         goto cleanup;
     }
-
-    if (VIR_STRDUP(ret, process) < 0)
+    if (!callerTime) {
+        virAccessError(VIR_ERR_INTERNAL_ERROR, "%s",
+                       _("No UNIX process start time available"));
+        goto cleanup;
+    }
+    if (!callerUid) {
+        virAccessError(VIR_ERR_INTERNAL_ERROR, "%s",
+                       _("No UNIX caller UID available"));
         goto cleanup;
+    }
+
+#ifdef PKCHECK_SUPPORTS_UID
+    supportsuid = true;
+#endif
+    if (supportsuid) {
+        if (virAsprintf(&ret, "%s,%s,%s", callerPid, callerTime, callerUid) < 0)
+            goto cleanup;
+    } else {
+        if (!polkitInsecureWarned) {
+            VIR_WARN("No support for caller UID with pkcheck. This deployment is known to be insecure.");
+            polkitInsecureWarned = true;
+        }
+        if (virAsprintf(&ret, "%s,%s", callerPid, callerTime) < 0)
+            goto cleanup;
+    }
 
 cleanup:
     virObjectUnref(identity);