Only allow the UNIX transport in remote driver when setuid

We don't know enough about quality of external libraries used
for non-UNIX transports, nor do we want to spawn external
commands when setuid. Restrict to the bare minimum which is
UNIX transport for local usage. Users shouldn't need to be
running setuid if connecting to remote hypervisors in any
case.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

src/libvirt.c

@@ -1135,6 +1135,12 @@ do_open(const char *name,
     if (name && name[0] == '\0')
         name = NULL;
 
+    if (!name && virIsSUID()) {
+        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                       _("An explicit URI must be provided when setuid"));
+        goto failed;
+    }
+
     /*
      *  If no URI is passed, then check for an environment string if not
      *  available probe the compiled in drivers to find a default hypervisor

src/remote/remote_driver.c

@@ -488,6 +488,20 @@ doRemoteOpen(virConnectPtr conn,
         transport = trans_unix;
     }
 
+    /*
+     * We don't want to be executing external programs in setuid mode,
+     * so this rules out 'ext' and 'ssh' transports. Exclude libssh
+     * and tls too, since we're not confident the libraries are safe
+     * for setuid usage. Just allow UNIX sockets, since that does
+     * not require any external libraries or command execution
+     */
+    if (virIsSUID() &&
+        transport != trans_unix) {
+        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                       _("Only Unix socket URI transport is allowed in setuid mode"));
+        return VIR_DRV_OPEN_ERROR;
+    }
+
     /* Local variables which we will initialize. These can
      * get freed in the failed: path.
      */