USBFS Bugfix

Markus Rechberger mrechberger at
Wed Mar 24 16:21:52 UTC 2010


on IRC I was recommended to submit this information to the mailinglist

Here's a better solution.  In theory we could copy just the individual
packets from within the transfer buffer, but that would probably take
longer than simply copying the whole buffer.

(This was a little hasty; I haven't even compile-tested the patch.
Some small fixes may be needed.)

Alan Stern

This patch fixes a bug in the way isochronous input data is returned
to userspace for usbfs transfers.  The entire buffer must be copied,
not just the first actual_length bytes, because the individual packets
will be discontiguous if any of them are short.

Signed-off-by: Alan Stern <stern at>
CC: stable <stable at>

Index: usb-2.6/drivers/usb/core/devio.c
--- usb-2.6.orig/drivers/usb/core/devio.c
+++ usb-2.6/drivers/usb/core/devio.c
@@ -1176,6 +1176,13 @@ static int proc_do_submiturb(struct dev_
 			return -ENOMEM;
+		/* Isochronous input data may end up being discontiguous
+		 * if some of the packets are short.  Clear the buffer so
+		 * that the gaps don't leak kernel data to userspace.
+		 */
+		if (is_in && uurb->type == USBDEVFS_URB_TYPE_ISO)
+			memset(as->urb->transfer_buffer, 0,
+					uurb->buffer_length);
 	as->urb->dev = ps->dev;
 	as->urb->pipe = (uurb->type << 30) |
@@ -1312,10 +1319,14 @@ static int processcompl(struct async *as
 	void __user *addr = as->userurb;
 	unsigned int i;

-	if (as->userbuffer && urb->actual_length)
-		if (copy_to_user(as->userbuffer, urb->transfer_buffer,
-				 urb->actual_length))
+	if (as->userbuffer && urb->actual_length) {
+		if (urb->number_of_packets > 0)		/* Isochronous */
+			i = urb->transfer_buffer_length;
+		else					/* Non-Isoc */
+			i = urb->actual_length;
+		if (copy_to_user(as->userbuffer, urb->transfer_buffer, i))
 			goto err_out;
+	}
 	if (put_user(as->status, &userurb->status))
 		goto err_out;
 	if (put_user(urb->actual_length, &userurb->actual_length))

It would be nice if this patch could go into the ubuntu lucid kernel
as soon as possible.


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