linux-kernel - [67/68] xhci: Fix errors in the running total calculations in the TRB math

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Message-Id: <20110228162412.397726637@clark.kroah.org>
Date:	Mon, 28 Feb 2011 08:23:28 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Paul Zimmerman <paulz@...opsys.com>,
	Sarah Sharp <sarah.a.sharp@...ux.intel.com>
Subject: [67/68] xhci: Fix errors in the running total calculations in the TRB math

2.6.32-longterm review patch.  If anyone has any objections, please let us know.

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

From: Paul Zimmerman <Paul.Zimmerman@...opsys.com>

commit 5807795bd4dececdf553719cc02869e633395787 upstream.

Calculations like

	running_total = TRB_MAX_BUFF_SIZE -
		(sg_dma_address(sg) & (TRB_MAX_BUFF_SIZE - 1));
	if (running_total != 0)
		num_trbs++;

are incorrect, because running_total can never be zero, so the if()
expression will never be true. I think the intention was that
running_total be in the range of 0 to TRB_MAX_BUFF_SIZE-1, not 1
to TRB_MAX_BUFF_SIZE. So adding a

	running_total &= TRB_MAX_BUFF_SIZE - 1;

fixes the problem.

This patch should be queued for stable kernels back to 2.6.31.

Signed-off-by: Paul Zimmerman <paulz@...opsys.com>
Signed-off-by: Sarah Sharp <sarah.a.sharp@...ux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 drivers/usb/host/xhci-ring.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -1491,6 +1491,7 @@ static unsigned int count_sg_trbs_needed
 		/* Scatter gather list entries may cross 64KB boundaries */
 		running_total = TRB_MAX_BUFF_SIZE -
 			(sg_dma_address(sg) & (TRB_MAX_BUFF_SIZE - 1));
+		running_total &= TRB_MAX_BUFF_SIZE - 1;
 		if (running_total != 0)
 			num_trbs++;
 
@@ -1740,6 +1741,7 @@ int xhci_queue_bulk_tx(struct xhci_hcd *
 	/* How much data is (potentially) left before the 64KB boundary? */
 	running_total = TRB_MAX_BUFF_SIZE -
 		(urb->transfer_dma & (TRB_MAX_BUFF_SIZE - 1));
+	running_total &= TRB_MAX_BUFF_SIZE - 1;
 
 	/* If there's some data on this 64KB chunk, or we have to send a
 	 * zero-length transfer, we need at least one TRB


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