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From: Miklos Szeredi <miklos@szeredi.hu>
To: Amir Goldstein <amir73il@gmail.com>
Cc: Vivek Goyal <vgoyal@redhat.com>,
	Al Viro <viro@zeniv.linux.org.uk>,
	overlayfs <linux-unionfs@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	"#v4 . 16" <stable@vger.kernel.org>
Subject: Re: [PATCH v3 1/4] ovl: use insert_inode_locked4() to hash a newly created inode
Date: Wed, 16 May 2018 12:14:58 +0200	[thread overview]
Message-ID: <CAJfpegtzd4+Atvu_i0bgfg1JXY1qsy6P5RrWWHCgXvODOy0pUg@mail.gmail.com> (raw)
In-Reply-To: <CAOQ4uxgjO=J-LtcrjtiE1cQDoV-3P1b=6+ixVQMBKnUm7WV+tQ@mail.gmail.com>

On Wed, May 16, 2018 at 11:51 AM, Amir Goldstein <amir73il@gmail.com> wrote:
> On Wed, May 16, 2018 at 11:34 AM, Miklos Szeredi <miklos@szeredi.hu> wrote:
>> On Tue, May 15, 2018 at 3:37 PM, Amir Goldstein <amir73il@gmail.com> wrote:
>>> On Tue, May 15, 2018 at 4:23 PM, Vivek Goyal <vgoyal@redhat.com> wrote:
>>>> On Tue, May 15, 2018 at 01:26:09PM +0300, Amir Goldstein wrote:
>>>>> Currently, there is a small window where ovl_obtain_alias() can
>>>>> race with ovl_instantiate() and create two different overlay inodes
>>>>> with the same underlying real non-dir non-hardlink inode.
>>>>>
>>>>> The race requires an adversary to guess the file handle of the
>>>>> yet to be created upper inode and decode the guessed file handle
>>>>> after ovl_creat_real(), but before ovl_instantiate().
>>>>>
>>>>> This patch fixes the race, by using insert_inode_locked4() to add
>>>>> a newly created inode to icache.
>>>>>
>>>>> If the newly created inode apears to already exist in icache (hashed
>>>>> by the same real upper inode), we export this error to user instead
>>>>> of silently not hashing the new inode.
>>>>
>>>> So we might return an error to user saying operation failed, but still
>>>> create file on upper. Does that sound little odd?
>>>>
>>>
>>> Yes, but I don't see a better solution.
>>
>> Might be better to kick the other, offending inode out, instead of
>> returning an error.  It would also simplify the error handling.
>>
>> We can do that by creating an ovl_inode_test_kick() variant that
>> unhashes the inode on match.  Also needs insert_inode_locked4() to use
>> hlist_for_each_entry_safe() instead of hlist_for_each_entry().
>>
>
> Do you really think that this corner use case calls for such actions,
> as creating flavors of inode cache helpers?

Yes, if it simplifies error handling.

> Remember that the so called "offending" inode, is not offending in
> a way that is wrong or incomplete in any way.

Right, so what about just using that inode instead of erroring out?

Thanks,
Miklos

  reply	other threads:[~2018-05-16 10:14 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-15 10:26 [PATCH v3 0/4] Overlayfs mkdir related fixes Amir Goldstein
2018-05-15 10:26 ` [PATCH v3 1/4] ovl: use insert_inode_locked4() to hash a newly created inode Amir Goldstein
2018-05-15 13:23   ` Vivek Goyal
2018-05-15 13:37     ` Amir Goldstein
2018-05-16  8:34       ` Miklos Szeredi
2018-05-16  9:51         ` Amir Goldstein
2018-05-16 10:14           ` Miklos Szeredi [this message]
2018-05-16 11:03             ` Amir Goldstein
2018-05-17  6:03       ` Amir Goldstein
2018-05-17  8:10         ` Miklos Szeredi
2018-05-17  8:45           ` Amir Goldstein
2018-05-17  8:53           ` Miklos Szeredi
2018-05-17  8:58             ` Amir Goldstein
2018-05-17  9:07               ` Miklos Szeredi
2018-05-17 16:14                 ` Amir Goldstein
2018-05-15 10:26 ` [PATCH v3 2/4] ovl: relax WARN_ON() real inode attributes mismatch Amir Goldstein
2018-05-15 12:48   ` Vivek Goyal
2018-05-15 12:55     ` Amir Goldstein
2018-05-16 10:29   ` Miklos Szeredi
2018-05-16 11:06     ` Amir Goldstein
2018-05-16 11:18       ` Miklos Szeredi
2018-05-16 13:46         ` Amir Goldstein
2018-05-15 10:26 ` [PATCH v3 3/4] ovl: create helper ovl_create_temp() Amir Goldstein
2018-05-16 10:41   ` Miklos Szeredi
2018-05-16 11:15     ` Amir Goldstein
2018-05-16 11:37       ` Miklos Szeredi
2018-05-15 10:26 ` [PATCH v3 4/4] ovl: make ovl_create_real() cope with vfs_mkdir() safely Amir Goldstein

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