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

[Avri Altman]

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;
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> Cc: linux-scsi@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH v4 3/5] scsi: ufs: fix potential access NULL pointer while
> memcpy
> 
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> 
> 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

Attachment: 0001-scsi-ufshcd-Simplify-ufshcd_read_desc_param.patch
Description: 0001-scsi-ufshcd-Simplify-ufshcd_read_desc_param.patch