Commit 6912354a authored Nov 03, 2005 by Alan Stern Committed by Greg Kroah-Hartman Jan 04, 2006

[PATCH] USB: EHCI: fix conflation of buf == 0 with len == 0

When the ehci-hcd driver prepares a control URB, it tests for a
zero-length data stage by looking at the transfer_dma value instead of
the transfer_buffer_length. (In fact it does this even for non-control
URBs, which is an additional aspect of the same bug.)

However, under certain circumstances it's possible for transfer_dma to
be 0 while transfer_buffer_length is non-zero. This can happen when a
freshly allocated page (mapped to address 0 and marked Copy-On-Write,
but never written to) is used as the source buffer for an OUT transfer.
This patch (as598) fixes the problem.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

parent 959eea21

drivers/usb/host/ehci-q.c

+7 −7

Original line number	Diff line number	Diff line
		@@ -514,18 +514,18 @@ qh_urb_transaction (
		qtd->urb = urb;
		qtd_prev->hw_next = QTD_NEXT (qtd->qtd_dma);
		list_add_tail (&qtd->qtd_list, head);

		/* for zero length DATA stages, STATUS is always IN */
		if (len == 0)
		token \|= (1 /* "in" */ << 8);
		}

		/*
		* data transfer stage: buffer setup
		*/
		if (likely (len > 0))
		buf = urb->transfer_dma;
		else
		buf = 0;

		/* for zero length DATA stages, STATUS is always IN */
		if (!buf \|\| is_input)
		if (is_input)
		token \|= (1 /* "in" */ << 8);
		/* else it's already initted to "out" pid (0 << 8) */

		@@ -572,7 +572,7 @@ qh_urb_transaction (
		* control requests may need a terminating data "status" ack;
		* bulk ones may need a terminating short packet (zero length).
		*/
		if (likely (buf != 0)) {
		if (likely (urb->transfer_buffer_length != 0)) {
		int one_more = 0;

		if (usb_pipecontrol (urb->pipe)) {