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

From: Wenwen Wang
Date: Mon Apr 30 2018 - 18:44:31 EST

On Mon, Apr 30, 2018 at 5:38 PM, Dilger, Andreas
<andreas.dilger@xxxxxxxxx> wrote:
> On Apr 29, 2018, at 07:20, Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
>> On Sat, Apr 28, 2018 at 04:04:25PM +0000, Dilger, Andreas wrote:
>>> On Apr 27, 2018, at 17:45, Wenwen Wang <wang6495@xxxxxxx> 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,
> I don't think it fixes a real bug, but it makes the code a bit more clear,
> so I'm OK to land it (with minor corrections to commit message per above).
> Cheers, Andreas
> --
> Andreas Dilger
> Lustre Principal Architect
> Intel Corporation

Thanks! I will re-submit the patch with the corrected commit message.