Patch "USB: usbfs: compute urb->actual_length for isochronous" has been added to the 3.18-stable tree

This is a note to let you know that I've just added the patch titled

    USB: usbfs: compute urb->actual_length for isochronous

to the 3.18-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
usb-usbfs-compute-urb-actual_length-for-isochronous.patch
and it can be found in the queue-3.18 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Alan Stern <[email protected]>
Date: Wed, 8 Nov 2017 12:23:17 -0500
Subject: USB: usbfs: compute urb->actual_length for isochronous

From: Alan Stern <[email protected]>

commit 2ef47001b3ee3ded579b7532ebdcf8680e4d8c54 upstream.

The USB kerneldoc says that the actual_length field "is read in non-iso completion functions", but the usbfs driver uses it for all URB types in processcompl(). Since not all of the host controller drivers set actual_length for isochronous URBs, programs using usbfs with some host controllers don't work properly. For example, Minas reports that a USB camera controlled by libusb doesn't work properly with a dwc2 controller.

It doesn't seem worthwhile to change the HCDs and the documentation, since the in-kernel USB class drivers evidently don't rely on actual_length for isochronous transfers. The easiest solution is for usbfs to calculate the actual_length value for itself, by adding up the lengths of the individual packets in an isochronous transfer.

---
 drivers/usb/core/devio.c |   14 ++++++++++++++
 1 file changed, 14 insertions(+)

@@ -1649,6 +1649,18 @@ static int proc_unlinkurb(struct usb_dev
 	return 0;
 }
 
+static void compute_isochronous_actual_length(struct urb *urb)
+{
+	unsigned int i;
+
+	if (urb->number_of_packets > 0) {
+		urb->actual_length = 0;
+		for (i = 0; i < urb->number_of_packets; i++)
+			urb->actual_length +=
+					urb->iso_frame_desc[i].actual_length;
+	}
+}
+
 static int processcompl(struct async *as, void __user * __user *arg)
 {
 	struct urb *urb = as->urb;

@@ -1656,6 +1668,7 @@ static int processcompl(struct async *as
 	void __user *addr = as->userurb;
 	unsigned int i;
 
+	compute_isochronous_actual_length(urb);
 	if (as->userbuffer && urb->actual_length) {
 		if (copy_urb_data_to_user(as->userbuffer, urb))
 			goto err_out;

@@ -1825,6 +1838,7 @@ static int processcompl_compat(struct as
 	void __user *addr = as->userurb;
 	unsigned int i;
 
+	compute_isochronous_actual_length(urb);
 	if (as->userbuffer && urb->actual_length) {
 		if (copy_urb_data_to_user(as->userbuffer, urb))
 			return -EFAULT;

Patches currently in stable-queue which might be from [email protected] are

queue-3.18/usb-usbfs-compute-urb-actual_length-for-isochronous.patch