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

[Wenwen Wang]

On Fri, May 4, 2018 at 5:08 AM, Dilger, Andreas
<andreas.dilger@xxxxxxxxx> wrote:
> On May 3, 2018, at 22:19, Wenwen Wang <wang6495@xxxxxxx> wrote:
>>
>> On Tue, May 1, 2018 at 3:46 AM, Dan Carpenter <dan.carpenter@xxxxxxxxxx> 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.
>

But, if the user uses such a struct, the second fetch won't be
executed. This is a little bit different from using LOV_MAGIC_V3
firstly and then changing it to LOV_MAGIC_V1.

Wenwen