linux-kernel - Re: [PATCH] ceph: check i_nlink while converting a file handle to dentry

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Date:   Thu, 18 May 2017 17:48:05 +0100
From:   Luis Henriques <lhenriques@...e.com>
To:     "Yan, Zheng" <zyan@...hat.com>
Cc:     Sage Weil <sage@...hat.com>, Ilya Dryomov <idryomov@...il.com>,
        ceph-devel <ceph-devel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ceph: check i_nlink while converting a file handle to
 dentry

On Thu, May 18, 2017 at 09:36:44PM +0800, Yan, Zheng wrote:
> 
> > On 17 May 2017, at 19:21, Luis Henriques <lhenriques@...e.com> wrote:
> > 
> > Converting a file handle to a dentry can be done call after the inode
> > unlink.  This means that __fh_to_dentry() requires an extra check to
> > verify the number of links is not 0.
> > 
> > The issue can be easily reproduced using xfstest generic/426, which does
> > something like:
> > 
> >  name_to_handle_at(&fh)
> >  echo 3 > /proc/sys/vm/drop_caches
> >  unlink()
> >  open_by_handle_at(&fh)
> > 
> > The call to open_by_handle_at() should fail, as the file doesn't exist
> > anymore.
> > 
> > Cc: stable@...r.kernel.org
> > Link: http://tracker.ceph.com/issues/19958
> > Signed-off-by: Luis Henriques <lhenriques@...e.com>
> > ---
> > fs/ceph/export.c | 4 ++++
> > 1 file changed, 4 insertions(+)
> > 
> > diff --git a/fs/ceph/export.c b/fs/ceph/export.c
> > index e8f11fa565c5..7df550c13d7f 100644
> > --- a/fs/ceph/export.c
> > +++ b/fs/ceph/export.c
> > @@ -91,6 +91,10 @@ static struct dentry *__fh_to_dentry(struct super_block *sb, u64 ino)
> > 		ceph_mdsc_put_request(req);
> > 		if (!inode)
> > 			return ERR_PTR(-ESTALE);
> > +		if (inode->i_nlink == 0) {
> > +			iput(inode);
> > +			return ERR_PTR(-ESTALE);
> > +		}
> > 	}
> 
> maybe we should do this check in MDS

Thank you for your review.  Are you suggesting to do this check *only* in
the MDS?  I guess that's probably a good thing to do too, but don't you
think it's a good idea to keep it on the client side as well?

Cheers,
--
Luís