linux-kernel - Re: [PATCH 3/4] vfio: ccw: set ccw->cda to NULL defensively

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Date:   Tue, 27 Mar 2018 12:03:18 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     Dong Jia Shi <bjsdjshi@...ux.vnet.ibm.com>
Cc:     linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        kvm@...r.kernel.org, borntraeger@...ibm.com,
        pasic@...ux.vnet.ibm.com, pmorel@...ux.vnet.ibm.com
Subject: Re: [PATCH 3/4] vfio: ccw: set ccw->cda to NULL defensively

On Tue, 27 Mar 2018 11:08:09 +0800
Dong Jia Shi <bjsdjshi@...ux.vnet.ibm.com> wrote:

> * Cornelia Huck <cohuck@...hat.com> [2018-03-26 15:47:53 +0200]:
> 
> > On Wed, 21 Mar 2018 03:08:21 +0100
> > Dong Jia Shi <bjsdjshi@...ux.vnet.ibm.com> wrote:
> >   
> > > Let's avoid free on ccw->cda that points to a guest address
> > > or a already freed memory area by setting it to NULL if memory
> > > allocation didn't happen or failed.  
> > 
> > Does not hurt, I guess.
> >   
> > > 
> > > Signed-off-by: Dong Jia Shi <bjsdjshi@...ux.vnet.ibm.com>
> > > ---
> > >  drivers/s390/cio/vfio_ccw_cp.c | 28 +++++++++++++++++++---------
> > >  1 file changed, 19 insertions(+), 9 deletions(-)
> > > 
> > > diff --git a/drivers/s390/cio/vfio_ccw_cp.c b/drivers/s390/cio/vfio_ccw_cp.c
> > > index 3abc9770910a..5958c35ab343 100644
> > > --- a/drivers/s390/cio/vfio_ccw_cp.c
> > > +++ b/drivers/s390/cio/vfio_ccw_cp.c
> > > @@ -491,7 +491,7 @@ static int ccwchain_fetch_direct(struct ccwchain *chain,
> > >  	struct ccw1 *ccw;
> > >  	struct pfn_array_table *pat;
> > >  	unsigned long *idaws;
> > > -	int idaw_nr;
> > > +	int idaw_nr, ret;
> > >  
> > >  	ccw = chain->ch_ccw + idx;
> > >  
> > > @@ -511,18 +511,20 @@ static int ccwchain_fetch_direct(struct ccwchain *chain,
> > >  	 * needed when translating a direct ccw to a idal ccw.
> > >  	 */
> > >  	pat = chain->ch_pat + idx;
> > > -	if (pfn_array_table_init(pat, 1))
> > > -		return -ENOMEM;
> > > -	idaw_nr = pfn_array_alloc_pin(pat->pat_pa, cp->mdev,
> > > +	ret = pfn_array_table_init(pat, 1);
> > > +	if (ret)
> > > +		goto out_init;
> > > +
> > > +	idaw_nr = ret = pfn_array_alloc_pin(pat->pat_pa, cp->mdev,  
> > 
> > Ugh, I don't like setting both at the same time... only set idaw_nr for
> > ret > 0? (personal preference)
> >   
> Ah, we don't need idaw_nr anymore. I think I should just replace it with
> ret.

Let's do that.

> 
> > >  				      ccw->cda, ccw->count);
> > > -	if (idaw_nr < 0)
> > > -		return idaw_nr;
> > > +	if (ret < 0)
> > > +		goto out_init;  
> >   
>