Linux: Stop kernel from re-attaching in-kernel driver after reset

When an interface is bound to the usbfs driver (iow claimed), the
kernel will unbind it, and then after the reset do a device_attach
on the interface, which will bind the default in kernel driver to
the interface.

So if an app has detached the in kernel driver, and claimed the
interface and then does a libusb_reset_device. Things end up with
the interface no longer being bound to the usbfs driver (so no longer
claimed) and instead it is bound to the in kernel driver (iow the in
kernel driver is re-attached).

We can stop this from happening by releasing all claimed interfaces
before the reset, as the kernel will not do the device attach after
reset, if no driver was bound to the interface before the reset.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>

1 files changed, 35 insertions, 5 deletions

diff --git a/libusb/os/linux_usbfs.c b/libusb/os/linux_usbfs.c
index b58861e..95c17b0 100644
--- a/libusb/os/linux_usbfs.c
+++ b/libusb/os/linux_usbfs.c
@@ -1340,17 +1340,47 @@ static int op_clear_halt(struct libusb_device_handle *handle,
 static int op_reset_device(struct libusb_device_handle *handle)
 {
 	int fd = __device_handle_priv(handle)->fd;
-	int r = ioctl(fd, IOCTL_USBFS_RESET, NULL);
+	int i, r, ret = 0;
+
+	/* Doing a device reset will cause the usbfs driver to get unbound
+	   from any interfaces it is bound to. By voluntarily unbinding
+	   the usbfs driver ourself, we stop the kernel from rebinding
+	   the interface after reset (which would end up with the interface
+	   getting bound to the in kernel driver if any). */
+	for (i = 0; i < USB_MAXINTERFACES; i++) {
+		if (handle->claimed_interfaces & (1L << i)) {
+			op_release_interface(handle, i);
+		}
+	}
+
+	usbi_mutex_lock(&handle->lock);
+	r = ioctl(fd, IOCTL_USBFS_RESET, NULL);
 	if (r) {
-		if (errno == ENODEV)
-			return LIBUSB_ERROR_NOT_FOUND;
+		if (errno == ENODEV) {
+			ret = LIBUSB_ERROR_NOT_FOUND;
+			goto out;
+		}
 
 		usbi_err(HANDLE_CTX(handle),
 			"reset failed error %d errno %d", r, errno);
-		return LIBUSB_ERROR_OTHER;
+		ret = LIBUSB_ERROR_OTHER;
+		goto out;
 	}
 
-	return 0;
+	/* And re-claim any interfaces which were claimed before the reset */
+	for (i = 0; i < USB_MAXINTERFACES; i++) {
+		if (handle->claimed_interfaces & (1L << i)) {
+			r = op_claim_interface(handle, i);
+			if (r) {
+				usbi_warn(HANDLE_CTX(handle),
+					"failed to re-claim interface %d after reset", i);
+				handle->claimed_interfaces &= ~(1L << i);
+			}
+		}
+	}
+out:
+	usbi_mutex_unlock(&handle->lock);
+	return ret;
 }
 
 static int op_kernel_driver_active(struct libusb_device_handle *handle,