[efi] Leave USB endpoint descriptors in existence until device is removed

Some UEFI USB drivers (observed with the keyboard driver on a
Microsoft Surface Go) will react to an asynchronous USB transfer
failure by terminating the transfer from within the completion
handler.  This closes the USB endpoint and, in the current
implementation, frees the containing structure.

This can lead to use-after-free bugs after the UEFI USB driver's
completion handler returns, since the calling code in iPXE expects
that a completion handler will not perform a control-flow action such
as terminating the transfer.

Fix by leaving the USB endpoint structure allocated until the device
is finally removed, as is already done (as an optimisation) for
control and bulk transfers.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/interface/efi/efi_usb.c

@@ -79,7 +79,8 @@ static VOID EFIAPI efi_usb_timer ( EFI_EVENT event __unused,
 	usb_poll ( bus );
 
 	/* Refill endpoint */
-	usb_refill ( &usbep->ep );
+	if ( usbep->ep.open )
+		usb_refill ( &usbep->ep );
 }
 
 /**
@@ -117,6 +118,21 @@ static int efi_usb_mtu ( struct efi_usb_interface *usbintf,
 	return -ENOENT;
 }
 
+/**
+ * Check if endpoint is open
+ *
+ * @v usbintf		EFI USB interface
+ * @v endpoint		Endpoint address
+ * @ret is_open		Endpoint is open
+ */
+static int efi_usb_is_open ( struct efi_usb_interface *usbintf,
+			     unsigned int endpoint ) {
+	unsigned int index = USB_ENDPOINT_IDX ( endpoint );
+	struct efi_usb_endpoint *usbep = usbintf->endpoint[index];
+
+	return ( usbep && usbep->ep.open );
+}
+
 /**
  * Open endpoint
  *
@@ -139,6 +155,22 @@ static int efi_usb_open ( struct efi_usb_interface *usbintf,
 	EFI_STATUS efirc;
 	int rc;
 
+	/* Allocate structure, if needed.  Once allocated, we leave
+	 * the endpoint structure in place until the device is
+	 * removed, to work around external UEFI code that closes the
+	 * endpoint at illegal times.
+	 */
+	usbep = usbintf->endpoint[index];
+	if ( ! usbep ) {
+		usbep = zalloc ( sizeof ( *usbep ) );
+		if ( ! usbep ) {
+			rc = -ENOMEM;
+			goto err_alloc;
+		}
+		usbep->usbintf = usbintf;
+		usbintf->endpoint[index] = usbep;
+	}
+
 	/* Get endpoint MTU */
 	mtu = efi_usb_mtu ( usbintf, endpoint );
 	if ( mtu < 0 ) {
@@ -147,12 +179,6 @@ static int efi_usb_open ( struct efi_usb_interface *usbintf,
 	}
 
 	/* Allocate and initialise structure */
-	usbep = zalloc ( sizeof ( *usbep ) );
-	if ( ! usbep ) {
-		rc = -ENOMEM;
-		goto err_alloc;
-	}
-	usbep->usbintf = usbintf;
 	usb_endpoint_init ( &usbep->ep, usbdev->usb, driver );
 	usb_endpoint_describe ( &usbep->ep, endpoint, attributes, mtu, 0,
 				( interval << 3 /* microframes */ ) );
@@ -164,9 +190,6 @@ static int efi_usb_open ( struct efi_usb_interface *usbintf,
 		       strerror ( rc ) );
 		goto err_open;
 	}
-
-	/* Record opened endpoint */
-	usbintf->endpoint[index] = usbep;
 	DBGC ( usbdev, "USBDEV %s %s opened\n",
 	       usbintf->name, usb_endpoint_name ( &usbep->ep ) );
 
@@ -185,12 +208,10 @@ static int efi_usb_open ( struct efi_usb_interface *usbintf,
 
 	bs->CloseEvent ( usbep->event );
  err_event:
-	usbintf->endpoint[index] = usbep;
 	usb_endpoint_close ( &usbep->ep );
  err_open:
-	free ( usbep );
- err_alloc:
  err_mtu:
+ err_alloc:
 	return rc;
 }
 
@@ -216,12 +237,6 @@ static void efi_usb_close ( struct efi_usb_endpoint *usbep ) {
 	usb_endpoint_close ( &usbep->ep );
 	DBGC ( usbdev, "USBDEV %s %s closed\n",
 	       usbintf->name, usb_endpoint_name ( &usbep->ep ) );
-
-	/* Free endpoint */
-	free ( usbep );
-
-	/* Record closed endpoint */
-	usbintf->endpoint[index] = NULL;
 }
 
 /**
@@ -236,11 +251,31 @@ static void efi_usb_close_all ( struct efi_usb_interface *usbintf ) {
 	for ( i = 0 ; i < ( sizeof ( usbintf->endpoint ) /
 			    sizeof ( usbintf->endpoint[0] ) ) ; i++ ) {
 		usbep = usbintf->endpoint[i];
-		if ( usbep )
+		if ( usbep && usbep->ep.open )
 			efi_usb_close ( usbep );
 	}
 }
 
+/**
+ * Free all endpoints
+ *
+ * @v usbintf		EFI USB interface
+ */
+static void efi_usb_free_all ( struct efi_usb_interface *usbintf ) {
+	struct efi_usb_endpoint *usbep;
+	unsigned int i;
+
+	for ( i = 0 ; i < ( sizeof ( usbintf->endpoint ) /
+			    sizeof ( usbintf->endpoint[0] ) ) ; i++ ) {
+		usbep = usbintf->endpoint[i];
+		if ( usbep ) {
+			assert ( ! usbep->ep.open );
+			free ( usbep );
+			usbintf->endpoint[i] = NULL;
+		}
+	}
+}
+
 /**
  * Complete synchronous transfer
  *
@@ -286,7 +321,7 @@ static int efi_usb_sync_transfer ( struct efi_usb_interface *usbintf,
 	int rc;
 
 	/* Open endpoint, if applicable */
-	if ( ( ! usbintf->endpoint[index] ) &&
+	if ( ( ! efi_usb_is_open ( usbintf, endpoint ) ) &&
 	     ( ( rc = efi_usb_open ( usbintf, endpoint, attributes, 0,
 				     &efi_usb_sync_driver ) ) != 0 ) ) {
 		goto err_open;
@@ -384,8 +419,12 @@ static void efi_usb_async_complete ( struct usb_endpoint *ep,
 			  status );
 
  drop:
-	/* Recycle I/O buffer */
+	/* Recycle or free I/O buffer */
-	usb_recycle ( &usbep->ep, iobuf );
+	if ( usbep->ep.open ) {
+		usb_recycle ( &usbep->ep, iobuf );
+	} else {
+		free_iob ( iobuf );
+	}
 }
 
 /** Asynchronous endpoint operations */
@@ -416,6 +455,12 @@ static int efi_usb_async_start ( struct efi_usb_interface *usbintf,
 	EFI_STATUS efirc;
 	int rc;
 
+	/* Fail if endpoint is already open */
+	if ( efi_usb_is_open ( usbintf, endpoint ) ) {
+		rc = -EINVAL;
+		goto err_already_open;
+	}
+
 	/* Open endpoint */
 	if ( ( rc = efi_usb_open ( usbintf, endpoint,
 				   USB_ENDPOINT_ATTR_INTERRUPT, interval,
@@ -453,6 +498,7 @@ static int efi_usb_async_start ( struct efi_usb_interface *usbintf,
  err_prefill:
 	efi_usb_close ( usbep );
  err_open:
+ err_already_open:
 	return rc;
 }
 
@@ -469,9 +515,9 @@ static void efi_usb_async_stop ( struct efi_usb_interface *usbintf,
 	unsigned int index = USB_ENDPOINT_IDX ( endpoint );
 
 	/* Do nothing if endpoint is already closed */
-	usbep = usbintf->endpoint[index];
+	if ( ! efi_usb_is_open ( usbintf, endpoint ) )
-	if ( ! usbep )
 		return;
+	usbep = usbintf->endpoint[index];
 
 	/* Stop timer */
 	bs->SetTimer ( usbep->event, TimerCancel, 0 );
@@ -1122,13 +1168,14 @@ static int efi_usb_install ( struct efi_usb_device *usbdev,
 	       usbintf->name, efi_handle_name ( usbintf->handle ) );
 	return 0;
 
-	efi_usb_close_all ( usbintf );
 	bs->UninstallMultipleProtocolInterfaces (
 			usbintf->handle,
 			&efi_usb_io_protocol_guid, &usbintf->usbio,
 			&efi_device_path_protocol_guid, usbintf->path,
 			NULL );
  err_install_protocol:
+	efi_usb_close_all ( usbintf );
+	efi_usb_free_all ( usbintf );
 	list_del ( &usbintf->list );
 	free ( usbintf );
  err_alloc:
@@ -1142,9 +1189,10 @@ static int efi_usb_install ( struct efi_usb_device *usbdev,
  */
 static void efi_usb_uninstall ( struct efi_usb_interface *usbintf ) {
 	EFI_BOOT_SERVICES *bs = efi_systab->BootServices;
+	struct efi_usb_device *usbdev = usbintf->usbdev;
 
-	/* Close all endpoints */
+	DBGC ( usbdev, "USBDEV %s uninstalling %s\n",
-	efi_usb_close_all ( usbintf );
+	       usbintf->name, efi_handle_name ( usbintf->handle ) );
 
 	/* Uninstall protocols */
 	bs->UninstallMultipleProtocolInterfaces (
@@ -1153,6 +1201,10 @@ static void efi_usb_uninstall ( struct efi_usb_interface *usbintf ) {
 			&efi_device_path_protocol_guid, usbintf->path,
 			NULL );
 
+	/* Close and free all endpoints */
+	efi_usb_close_all ( usbintf );
+	efi_usb_free_all ( usbintf );
+
 	/* Remove from list of interfaces */
 	list_del ( &usbintf->list );