[3.8.y.z extended stable] Patch "xen/blkback: fix reference counting" has been added to staging queue

[Kamal Mostafa]

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

    xen/blkback: fix reference counting

to the linux-3.8.y-queue branch of the 3.8.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-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.14.

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

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From e8aceb485a8fe05aebdec0c75a0af2b204355de9 Mon Sep 17 00:00:00 2001
From: Vegard Nossum <vegard.nossum at oracle.com>
Date: Thu, 5 Sep 2013 13:00:14 +0200
Subject: xen/blkback: fix reference counting

commit ea5ec76d76da9279d12027c1828544c5ccbe7932 upstream.

If the permission check fails, we drop a reference to the blkif without
having taken it in the first place. The bug was introduced in commit
604c499cbbcc3d5fe5fb8d53306aa0fae1990109 (xen/blkback: Check device
permissions before allowing OP_DISCARD).

Cc: Jan Beulich <JBeulich at suse.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
Signed-off-by: Vegard Nossum <vegard.nossum at oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
Signed-off-by: Jens Axboe <axboe at kernel.dk>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/block/xen-blkback/blkback.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
index bdee5f8..088f012 100644
--- a/drivers/block/xen-blkback/blkback.c
+++ b/drivers/block/xen-blkback/blkback.c
@@ -658,6 +658,8 @@ static int dispatch_discard_io(struct xen_blkif *blkif,
 	unsigned long secure;
 	struct phys_req preq;

+	xen_blkif_get(blkif);
+
 	preq.sector_number = req->u.discard.sector_number;
 	preq.nr_sects      = req->u.discard.nr_sectors;

@@ -670,7 +672,6 @@ static int dispatch_discard_io(struct xen_blkif *blkif,
 	}
 	blkif->st_ds_req++;

-	xen_blkif_get(blkif);
 	secure = (blkif->vbd.discard_secure &&
 		 (req->u.discard.flag & BLKIF_DISCARD_SECURE)) ?
 		 BLKDEV_DISCARD_SECURE : 0;
--
1.8.3.2