linux-kernel - [015/111] blkdev: cgroup whitelist permission fix

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Message-Id: <20100811235456.974518113@clark.site>
Date:	Wed, 11 Aug 2010 16:53:56 -0700
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,
	Chris Wright <chrisw@...s-sol.org>,
	"Serge E. Hallyn" <serue@...ibm.com>,
	Al Viro <viro@...IV.linux.org.uk>,
	Christoph Hellwig <hch@...radead.org>,
	"Daniel P. Berrange" <berrange@...hat.com>
Subject: [015/111] blkdev: cgroup whitelist permission fix

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

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

From: Chris Wright <chrisw@...s-sol.org>

commit b7300b78d1a87625975a799a109a2f98d77757c8 upstream.

The cgroup device whitelist code gets confused when trying to grant
permission to a disk partition that is not currently open.  Part of
blkdev_open() includes __blkdev_get() on the whole disk.

Basically, the only ways to reliably allow a cgroup access to a partition
on a block device when using the whitelist are to 1) also give it access
to the whole block device or 2) make sure the partition is already open in
a different context.

The patch avoids the cgroup check for the whole disk case when opening a
partition.

Addresses https://bugzilla.redhat.com/show_bug.cgi?id=589662

Signed-off-by: Chris Wright <chrisw@...s-sol.org>
Acked-by: Serge E. Hallyn <serue@...ibm.com>
Tested-by: Serge E. Hallyn <serue@...ibm.com>
Reported-by: Vivek Goyal <vgoyal@...hat.com>
Cc: Al Viro <viro@...IV.linux.org.uk>
Cc: Christoph Hellwig <hch@...radead.org>
Cc: "Daniel P. Berrange" <berrange@...hat.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 fs/block_dev.c |   10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1175,10 +1175,12 @@ static int __blkdev_get(struct block_dev
 	/*
 	 * hooks: /n/, see "layering violations".
 	 */
-	ret = devcgroup_inode_permission(bdev->bd_inode, perm);
-	if (ret != 0) {
-		bdput(bdev);
-		return ret;
+	if (!for_part) {
+		ret = devcgroup_inode_permission(bdev->bd_inode, perm);
+		if (ret != 0) {
+			bdput(bdev);
+			return ret;
+		}
 	}

 	lock_kernel();

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