RE: [PATCH v4 3/5] scsi: ufs: fix potential access NULL pointer while memcpy

[Avri Altman]

But this is just a suggestion.
Your way is fine too.

Thanks,
Avri

> 
> How about something like the untested attached?
> 
> Thanks,
> Avri
> 
> > -----Original Message-----
> > From: Bean Huo <huobean@xxxxxxxxx>
> > Sent: Tuesday, June 2, 2020 2:36 PM
> > To: Avri Altman <Avri.Altman@xxxxxxx>; alim.akhtar@xxxxxxxxxxx;
> > asutoshd@xxxxxxxxxxxxxx; jejb@xxxxxxxxxxxxx;
> > martin.petersen@xxxxxxxxxx; stanley.chu@xxxxxxxxxxxx;
> > beanhuo@xxxxxxxxxx; bvanassche@xxxxxxx; tomas.winkler@xxxxxxxxx;
> > cang@xxxxxxxxxxxxxx
> > Cc: linux-scsi@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> > Subject: Re: [PATCH v4 3/5] scsi: ufs: fix potential access NULL pointer while
> > memcpy
> >
> > CAUTION: This email originated from outside of Western Digital. Do not click
> > on links or open attachments unless you recognize the sender and know
> that
> > the content is safe.
> >
> >
> > hi Avri
> > thanks review.
> >
> >
> > On Mon, 2020-06-01 at 06:25 +0000, Avri Altman wrote:
> > > Hi,
> > >
> > > > If param_offset is not 0, the memcpy length shouldn't be the
> > > > true descriptor length.
> > > >
> > > > Fixes: a4b0e8a4e92b ("scsi: ufs: Factor out
> > > > ufshcd_read_desc_param")
> > > > Signed-off-by: Bean Huo <beanhuo@xxxxxxxxxx>
> > > > ---
> > > >  drivers/scsi/ufs/ufshcd.c | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> > > > index f7e8bfefe3d4..bc52a0e89cd3 100644
> > > > --- a/drivers/scsi/ufs/ufshcd.c
> > > > +++ b/drivers/scsi/ufs/ufshcd.c
> > > > @@ -3211,7 +3211,7 @@ int ufshcd_read_desc_param(struct ufs_hba
> > > > *hba,
> > > >
> > > >         /* Check wherher we will not copy more data, than available
> > > > */
> > > >         if (is_kmalloc && param_size > buff_len)
> > > > -               param_size = buff_len;
> > > > +               param_size = buff_len - param_offset;
> > >
> > > But Is_kmalloc is true if (param_offset != 0 || param_size <
> > > buff_len)
> > > So  if (is_kmalloc && param_size > buff_len) implies that
> > > param_offset is 0,
> > > Or did I get it wrong?
> >
> > If param_offset is 0, This willn't get any wrong, after this patch, it
> > is the same since offset is 0. As mentioned in the commit message, this
> > patch is only for the case of param_offset is not 0.
> >
> > >
> > > Still, I think that there is a problem here because nowhere we are
> > > checking that
> > > param_offset + param_size < buff_len, which now can happen because of
> > > ufs-bsg.
> > > Maybe you can add it and get rid of that is_kmalloc which is an
> > > awkward way to test for valid values?
> >
> > let me explain further:
> > we have these conditinos:
> >
> > 1) param_offset == 0, param_size >= buff_len;//no problem,
> > ufshcd_query_descriptor_retry() will read descripor with true
> > descriptor length, and no memcpy() called.
> >
> >
> > 2) param_offset == 0, param_size < buff_len;// no problem,
> > ufshcd_query_descriptor_retry() will read descripor with true
> > descriptor length buff_len, and memcpy() with param_size length.
> >
> >
> > 3) param_offset != 0, param_offset + param_size <= buff_len;// no
> > problem, ufshcd_query_descriptor_retry() will read descripor with true
> > descriptor length, and memcpy() with param_size length.
> >
> >
> > 4) param_offset != 0, param_offset + param_size > buff_len;// NULL
> > pointer reference problem, since ufshcd_query_descriptor_retry() will
> > read descripor with true descriptor length, and memcpy() with buff_len
> > length. correct memcpy length should be (buff_len - param_offset)
> >
> > param_offset + param_size < buff_len doesn't need to add, and
> > is_kmalloc is very hard to be removed based on current flow.
> >
> > so, the correct fixup patch shoulbe be like this:
> >
> >
> > -if (is_kmalloc && param_size > buff_len)
> > -       param_size = buff_len
> > +if (is_kmalloc && (param_size + param_offset) > buff_len)
> > +       param_size = buff_len - param_offset;
> >
> >
> > how do you think about it? if no problem, I will update it in next
> > version patch.
> >
> > thanks,
> >
> > Bean