linux-kernel - RE: [PATCH 12/29] drivers, media: convert s2255_dev.num_channels from atomic_t to refcount

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <2236FBA76BA1254E88B949DDB74E612B41C558C5@IRSMSX102.ger.corp.intel.com>
Date:   Tue, 7 Mar 2017 14:45:45 +0000
From:   "Reshetova, Elena" <elena.reshetova@...el.com>
To:     Sakari Ailus <sakari.ailus@....fi>
CC:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux1394-devel@...ts.sourceforge.net" 
        <linux1394-devel@...ts.sourceforge.net>,
        "linux-bcache@...r.kernel.org" <linux-bcache@...r.kernel.org>,
        "linux-raid@...r.kernel.org" <linux-raid@...r.kernel.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        "fcoe-devel@...n-fcoe.org" <fcoe-devel@...n-fcoe.org>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "open-iscsi@...glegroups.com" <open-iscsi@...glegroups.com>,
        "devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
        "target-devel@...r.kernel.org" <target-devel@...r.kernel.org>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        Hans Liljestrand <ishkamiel@...il.com>,
        Kees Cook <keescook@...omium.org>,
        David Windsor <dwindsor@...il.com>
Subject: RE: [PATCH 12/29] drivers, media: convert s2255_dev.num_channels
 from atomic_t to refcount_t


> Hi Elena,
> 
> On Mon, Mar 06, 2017 at 04:20:59PM +0200, Elena Reshetova wrote:
> > refcount_t type and corresponding API should be
> > used instead of atomic_t when the variable is used as
> > a reference counter. This allows to avoid accidental
> > refcounter overflows that might lead to use-after-free
> > situations.
> >
> > Signed-off-by: Elena Reshetova <elena.reshetova@...el.com>
> > Signed-off-by: Hans Liljestrand <ishkamiel@...il.com>
> > Signed-off-by: Kees Cook <keescook@...omium.org>
> > Signed-off-by: David Windsor <dwindsor@...il.com>
> > ---
> ...
> > @@ -1688,7 +1689,7 @@ static int s2255_probe_v4l(struct s2255_dev *dev)
> >  				"failed to register
> video device!\n");
> >  			break;
> >  		}
> > -		atomic_inc(&dev->num_channels);
> > +		refcount_set(&dev->num_channels, 1);
> 
> That's not right. The loop runs four iterations and the value after the
> loop should be indeed the number of channels.

Oh, yes, I was blind here, sorry. The problem why it cannot be left as inc is because it would do increment from zero here, which is not allowed by refcount_t interface. 

> atomic_t isn't really used for reference counting here, but storing out how
> many "channels" there are per hardware device, with maximum number of four
> (4). I'd leave this driver using atomic_t.
Yes, sounds like the best thing to do. I will drop this patch. 

Thank you for reviews!

Best Regards,
Elena.
> 
> >  		v4l2_info(&dev->v4l2_dev, "V4L2 device registered
> as %s\n",
> >  			  video_device_node_name(&vc-
> >vdev));
> >
> 
> --
> Kind regards,
> 
> Sakari Ailus
> e-mail: sakari.ailus@....fi	XMPP: sailus@...iisi.org.uk