[3.13.y-ckt stable] Patch "usb-storage: handle a skipped data phase" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    usb-storage: handle a skipped data phase

to the linux-3.13.y-queue branch of the 3.13.y-ckt extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11-ckt12.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From d70b19d719246b41f336d51cb748294da4e494f7 Mon Sep 17 00:00:00 2001
From: Alan Stern <stern at rowland.harvard.edu>
Date: Fri, 31 Oct 2014 14:49:47 -0400
Subject: usb-storage: handle a skipped data phase

commit 93c9bf4d1838d5851a18ca398b0ad66397f05056 upstream.

Sometimes mass-storage devices using the Bulk-only transport will
mistakenly skip the data phase of a command.  Rather than sending the
data expected by the host or sending a zero-length packet, they go
directly to the status phase and send the CSW.

This causes problems for usb-storage, for obvious reasons.  The driver
will interpret the CSW as a short data transfer and will wait to
receive a CSW.  The device won't have anything left to send, so the
command eventually times out.

The SCSI layer doesn't retry commands after they time out (this is a
relatively recent change).  Therefore we should do our best to detect
a skipped data phase and handle it promptly.

This patch adds code to do that.  If usb-storage receives a short
13-byte data transfer from the device, and if the first four bytes of
the data match the CSW signature, the driver will set the residue to
the full transfer length and interpret the data as a CSW.

This fixes Bugzilla #86611.

Signed-off-by: Alan Stern <stern at rowland.harvard.edu>
CC: Matthew Dharm <mdharm-usb at one-eyed-alien.net>
Tested-by: Paul Osmialowski <newchief at king.net.pl>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/usb/storage/transport.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/drivers/usb/storage/transport.c b/drivers/usb/storage/transport.c
index 22c7d43..b1d815e 100644
--- a/drivers/usb/storage/transport.c
+++ b/drivers/usb/storage/transport.c
@@ -1118,6 +1118,31 @@ int usb_stor_Bulk_transport(struct scsi_cmnd *srb, struct us_data *us)
 		 */
 		if (result == USB_STOR_XFER_LONG)
 			fake_sense = 1;
+
+		/*
+		 * Sometimes a device will mistakenly skip the data phase
+		 * and go directly to the status phase without sending a
+		 * zero-length packet.  If we get a 13-byte response here,
+		 * check whether it really is a CSW.
+		 */
+		if (result == USB_STOR_XFER_SHORT &&
+				srb->sc_data_direction == DMA_FROM_DEVICE &&
+				transfer_length - scsi_get_resid(srb) ==
+					US_BULK_CS_WRAP_LEN) {
+			struct scatterlist *sg = NULL;
+			unsigned int offset = 0;
+
+			if (usb_stor_access_xfer_buf((unsigned char *) bcs,
+					US_BULK_CS_WRAP_LEN, srb, &sg,
+					&offset, FROM_XFER_BUF) ==
+						US_BULK_CS_WRAP_LEN &&
+					bcs->Signature ==
+						cpu_to_le32(US_BULK_CS_SIGN)) {
+				usb_stor_dbg(us, "Device skipped data phase\n");
+				scsi_set_resid(srb, transfer_length);
+				goto skipped_data_phase;
+			}
+		}
 	}

 	/* See flow chart on pg 15 of the Bulk Only Transport spec for
@@ -1153,6 +1178,7 @@ int usb_stor_Bulk_transport(struct scsi_cmnd *srb, struct us_data *us)
 	if (result != USB_STOR_XFER_GOOD)
 		return USB_STOR_TRANSPORT_ERROR;

+ skipped_data_phase:
 	/* check bulk status */
 	residue = le32_to_cpu(bcs->Residue);
 	usb_stor_dbg(us, "Bulk Status S 0x%x T 0x%x R %u Stat 0x%x\n",
--
1.9.1