From: Wenwen Wang <wang6495@umn.edu>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "devel@driverdev.osuosl.org" <devel@driverdev.osuosl.org>,
Aastha Gupta <aastha.gupta4104@gmail.com>,
"Dilger, Andreas" <andreas.dilger@intel.com>,
Jeff Layton <jlayton@redhat.com>,
"Drokin, Oleg" <oleg.drokin@intel.com>,
Wenwen Wang <wang6495@umn.edu>, "kjlu@umn.edu" <kjlu@umn.edu>,
NeilBrown <neilb@suse.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Ben Evans <bevans@cray.com>,
"lustre-devel@lists.lustre.org" <lustre-devel@lists.lustre.org>
Subject: Re: [PATCH] staging: luster: llite: fix a potential missing-check bug when copying lumv
Date: Sun, 29 Apr 2018 15:58:55 -0500 [thread overview]
Message-ID: <CAAa=b7dPWAsqfQOWzvecHqAHYuhA63_+ya6nOMdPQ7ZaL6JB9w@mail.gmail.com> (raw)
In-Reply-To: <20180429132058.GB5972@kroah.com>
On Sun, Apr 29, 2018 at 8:20 AM, Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
> On Sat, Apr 28, 2018 at 04:04:25PM +0000, Dilger, Andreas wrote:
>> On Apr 27, 2018, at 17:45, Wenwen Wang <wang6495@umn.edu> wrote:
>> > [PATCH] staging: luster: llite: fix potential missing-check bug when copying lumv
>>
>> (typo) s/luster/lustre/
>>
>> > In ll_dir_ioctl(), the object lumv3 is firstly copied from the user space
>> > using Its address, i.e., lumv1 = &lumv3. If the lmm_magic field of lumv3 is
>> > LOV_USER_MAGIV_V3, lumv3 will be modified by the second copy from the user
>>
>> (typo) s/MAGIV/MAGIC/
>>
>> > space. The second copy is necessary, because the two versions (i.e.,
>> > lov_user_md_v1 and lov_user_md_v3) have different data formats and lengths.
>> > 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 isn't a serious bug in the end. The LOV_USER_MAGIC_V3 check just copies
>> a bit more data from userspace (the lmm_pool field). It would be more of a
>> problem if the reverse was possible (copy smaller V1 buffer, but change the
>> magic to LOV_USER_MAGIC_V3 afterward), but this isn't possible since the second
>> copy is not done if there is a V1 magic. If the user changes from V3 magic
>> to V1 in a racy manner it means less data will be used than copied, which
>> is harmless.
>>
>> > This patch rechecks the version field lmm_magic in the second copy. If the
>> > version is not as expected, i.e., LOV_USER_MAGIC_V3, an error code will be
>> > returned: -EINVAL.
>>
>> This isn't a bad idea in any case, since it verifies the data copied from
>> userspace is still valid.
>
> So you agree with this patch? Or do not?
>
> confused,
>
> greg k-h
It is worth fixing this bug, since it offers an opportunity for adversaries
to provide inconsistent user data. In addition to the unwanted version
LOV_USER_MAGIC_V1, a malicious user can also use the version
LMV_USER_MAGIC, which is also unexpected but allowed in the function
ll_dir_setstripe(). These inconsistent data can cause potential logical
errors in the following execution. Hence it is necessary to re-verify the
data copied from userspace.
Thanks!
Wenwen
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next prev parent reply other threads:[~2018-04-29 20:58 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-27 23:45 [PATCH] staging: luster: llite: fix a potential missing-check bug when copying lumv Wenwen Wang
2018-04-28 16:04 ` Dilger, Andreas
2018-04-29 13:20 ` Greg Kroah-Hartman
2018-04-29 20:58 ` Wenwen Wang [this message]
2018-04-30 11:15 ` Dan Carpenter
2018-04-30 22:38 ` Dilger, Andreas
2018-04-30 22:43 ` Wenwen Wang
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