[3.11.y.z extended stable] Patch "USB: cdc-acm: fix write and resume race" has been added to staging queue

[Luis Henriques]

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

    USB: cdc-acm: fix write and resume race

to the linux-3.11.y-queue branch of the 3.11.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.11.y-queue

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

For more information about the 3.11.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From e1f91ef102f28fa47cce38249a0497914b6908a0 Mon Sep 17 00:00:00 2001
From: Johan Hovold <jhovold at gmail.com>
Date: Mon, 26 May 2014 19:23:37 +0200
Subject: USB: cdc-acm: fix write and resume race

commit e144ed28bed10684f9aaec6325ed974d53f76110 upstream.

Fix race between write() and resume() due to improper locking that could
lead to writes being reordered.

Resume must be done atomically and susp_count be protected by the
write_lock in order to prevent racing with write(). This could otherwise
lead to writes being reordered if write() grabs the write_lock after
susp_count is decremented, but before the delayed urb is submitted.

Fixes: 11ea859d64b6 ("USB: additional power savings for cdc-acm devices
that support remote wakeup")

Signed-off-by: Johan Hovold <jhovold at gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/usb/class/cdc-acm.c | 23 +++++++++--------------
 1 file changed, 9 insertions(+), 14 deletions(-)

diff --git a/drivers/usb/class/cdc-acm.c b/drivers/usb/class/cdc-acm.c
index 6ebcd38dfb06..2d9601da87b3 100644
--- a/drivers/usb/class/cdc-acm.c
+++ b/drivers/usb/class/cdc-acm.c
@@ -1447,27 +1447,20 @@ static int acm_resume(struct usb_interface *intf)
 	struct acm *acm = usb_get_intfdata(intf);
 	struct acm_wb *wb;
 	int rv = 0;
-	int cnt;

 	spin_lock_irq(&acm->read_lock);
-	acm->susp_count -= 1;
-	cnt = acm->susp_count;
-	spin_unlock_irq(&acm->read_lock);
+	spin_lock(&acm->write_lock);

-	if (cnt)
-		return 0;
+	if (--acm->susp_count)
+		goto out;

 	if (test_bit(ASYNCB_INITIALIZED, &acm->port.flags)) {
-		rv = usb_submit_urb(acm->ctrlurb, GFP_NOIO);
+		rv = usb_submit_urb(acm->ctrlurb, GFP_ATOMIC);

-		spin_lock_irq(&acm->write_lock);
 		if (acm->delayed_wb) {
 			wb = acm->delayed_wb;
 			acm->delayed_wb = NULL;
-			spin_unlock_irq(&acm->write_lock);
 			acm_start_wb(acm, wb);
-		} else {
-			spin_unlock_irq(&acm->write_lock);
 		}

 		/*
@@ -1475,12 +1468,14 @@ static int acm_resume(struct usb_interface *intf)
 		 * do the write path at all cost
 		 */
 		if (rv < 0)
-			goto err_out;
+			goto out;

-		rv = acm_submit_read_urbs(acm, GFP_NOIO);
+		rv = acm_submit_read_urbs(acm, GFP_ATOMIC);
 	}
+out:
+	spin_unlock(&acm->write_lock);
+	spin_unlock_irq(&acm->read_lock);

-err_out:
 	return rv;
 }

--
1.9.1