fs: umount on symlink leaks mnt count

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@openvz.org>
Acked-by: Ian Kent <raven@themaw.net>
Acked-by: Jeff Layton <jlayton@primarydata.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

diff --git a/fs/namei.c b/fs/namei.c
index 338d08b7eae216392bd4d4b1f4f798a798c65349..e3249d565c95a9b2d8d61a2199de28cb8d733c1c 100644 (file)
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2281,9 +2281,10 @@ done:
                goto out;
        }
        path->dentry = dentry;
-       path->mnt = mntget(nd->path.mnt);
+       path->mnt = nd->path.mnt;
        if (should_follow_link(dentry->d_inode, nd->flags & LOOKUP_FOLLOW))
                return 1;
+       mntget(path->mnt);
        follow_mount(path);
        error = 0;
 out: