USB: devio: Don't corrupt user memory

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@rowland.harvard.edu>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/core/devio.c b/drivers/usb/core/devio.c
index e9326f31db8d4367cb80e813954573c983a49a08..4664e543cf2f88aa412615ffa5156148c67be23d 100644 (file)
--- a/drivers/usb/core/devio.c
+++ b/drivers/usb/core/devio.c
@@ -1576,7 +1576,11 @@ static int proc_do_submiturb(struct usb_dev_state *ps, struct usbdevfs_urb *uurb
                        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: