linux-kernel - Re: [PATCH v2] staging: lustre: llite: fix potential missing-check bug when copying lumv

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Message-ID: <7185D89D-A0FE-4B55-B089-9AF0891A00BF@intel.com>
Date:   Fri, 4 May 2018 10:08:16 +0000
From:   "Dilger, Andreas" <andreas.dilger@...el.com>
To:     Wenwen Wang <wang6495@....edu>
CC:     Dan Carpenter <dan.carpenter@...cle.com>,
        "open list:STAGING SUBSYSTEM" <devel@...verdev.osuosl.org>,
        Aastha Gupta <aastha.gupta4104@...il.com>,
        Roman Storozhenko <romeusmeister@...il.com>,
        Jeff Layton <jlayton@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kangjie Lu <kjlu@....edu>, NeilBrown <neilb@...e.com>,
        open list <linux-kernel@...r.kernel.org>,
        "Drokin, Oleg" <oleg.drokin@...el.com>,
        "moderated list:STAGING - LUSTRE PARALLEL FILESYSTEM" 
        <lustre-devel@...ts.lustre.org>
Subject: Re: [PATCH v2] staging: lustre: llite: fix potential missing-check
 bug when copying lumv

On May 3, 2018, at 22:19, Wenwen Wang <wang6495@....edu> wrote:
> 
> On Tue, May 1, 2018 at 3:46 AM, Dan Carpenter <dan.carpenter@...cle.com> wrote:
>> On Mon, Apr 30, 2018 at 05:56:10PM -0500, Wenwen Wang wrote:
>>> However, given that the user data resides in the user space, a malicious
>>> user-space process can race to change the data between the two copies. By
>>> doing so, the attacker can provide a data with an inconsistent version,
>>> e.g., v1 version + v3 data. This can lead to logical errors in the
>>> following execution in ll_dir_setstripe(), which performs different actions
>>> according to the version specified by the field lmm_magic.
>> 
>> This part is misleading.  The fix is to improve readability and make
>> static checkers happy.  You're over dramatizing it to make people think
>> it has a security impact when it doesn't.
>> 
>> If the user wants to specify v1 data they can just say that on the first
>> read.  They don't need to do funny tricks and race between the two
>> reads.  It's allowed.
>> 
>> In other words this allows the user to do something in a very
>> complicated way which they are already allowed to do in a very simple
>> straight forward way.
>> 
>> regards,
>> dan carpenter
> 
> Thanks for your comment, Dan! How about this:
> 
> However, given that the user data resides in the user space, a
> malicious user-space process can race to change the data between the
> two copies. By doing so, the attacker can provide a data with an
> inconsistent version, e.g., v1 version + v3 data. The current kernel
> can handle such inconsistent data. But, it may pose a potential
> security risk for future implementations. Also, to improve code
> readability and make static analysis tools happy, which will warn
> about read-verify-re-read type bugs, this issue should be fixed.

There is nothing preventing the user from using struct lov_mds_md_v3 but
filling in lmm_magic = LOV_MAGIC_V1 from the beginning, no need for a race.

Cheers, Andreas
--
Andreas Dilger
Lustre Principal Architect
Intel Corporation