[PATCH 4.9 017/105] USB: devio: Dont corrupt user memory

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Dan Carpenter <dan.carpenter@xxxxxxxxxx>

commit fa1ed74eb1c233be6131ec92df21ab46499a15b6 upstream.

The user buffer has "uurb->buffer_length" bytes.  If the kernel has more
information than that, we should truncate it instead of writing past
the end of the user's buffer.  I added a WARN_ONCE() to help the user
debug the issue.

Reported-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Acked-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/usb/core/devio.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/drivers/usb/core/devio.c
+++ b/drivers/usb/core/devio.c
@@ -1577,7 +1577,11 @@ static int proc_do_submiturb(struct usb_
 			totlen += isopkt[u].length;
 		}
 		u *= sizeof(struct usb_iso_packet_descriptor);
-		uurb->buffer_length = totlen;
+		if (totlen <= uurb->buffer_length)
+			uurb->buffer_length = totlen;
+		else
+			WARN_ONCE(1, "uurb->buffer_length is too short %d vs %d",
+				  totlen, uurb->buffer_length);
 		break;
 
 	default: