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

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Message-Id: <A5330653-F609-4CE7-BE15-AD80C671FAD2@redhat.com>
Date:   Fri, 19 May 2017 08:41:45 +0800
From:   "Yan, Zheng" <zyan@...hat.com>
To:     Luis Henriques <lhenriques@...e.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 19 May 2017, at 00:48, Luis Henriques <lhenriques@...e.com> wrote:
> 
> 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?

Applied. Thanks

Yan, Zheng

> 
> Cheers,
> --
> Luís