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

Greg Kroah-Hartman
2018-04-29T13:20:58Z

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