linux-kernel - [PATCH 3.15 28/37] fs: umount on symlink leaks mnt count

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Date:	Tue, 29 Jul 2014 18:49:04 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Vasily Averin <vvs@...nvz.org>,
	Ian Kent <raven@...maw.net>,
	Jeff Layton <jlayton@...marydata.com>,
	Christoph Hellwig <hch@....de>
Subject: [PATCH 3.15 28/37] fs: umount on symlink leaks mnt count

3.15-stable review patch.  If anyone has any objections, please let me know.

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

From: Vasily Averin <vvs@...allels.com>

commit 295dc39d941dc2ae53d5c170365af4c9d5c16212 upstream.

Currently umount on symlink blocks following umount:

/vz is separate mount

# ls /vz/ -al | grep test
drwxr-xr-x.  2 root root       4096 Jul 19 01:14 testdir
lrwxrwxrwx.  1 root root         11 Jul 19 01:16 testlink -> /vz/testdir
# umount -l /vz/testlink
umount: /vz/testlink: not mounted (expected)

# lsof /vz
# umount /vz
umount: /vz: device is busy. (unexpected)

In this case mountpoint_last() gets an extra refcount on path->mnt

Signed-off-by: Vasily Averin <vvs@...nvz.org>
Acked-by: Ian Kent <raven@...maw.net>
Acked-by: Jeff Layton <jlayton@...marydata.com>
Signed-off-by: Christoph Hellwig <hch@....de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/namei.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2256,9 +2256,10 @@ done:
 		goto out;
 	}
 	path->dentry = dentry;
-	path->mnt = mntget(nd->path.mnt);
+	path->mnt = nd->path.mnt;
 	if (should_follow_link(dentry, nd->flags & LOOKUP_FOLLOW))
 		return 1;
+	mntget(path->mnt);
 	follow_mount(path);
 	error = 0;
 out:


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