Re: [PATCH] staging: vt6655: fix direct dereferencing of user pointer

[Malcolm Priestley]

On 27/07/14 19:21, Greg Kroah-Hartman wrote:
> On Sat, Jul 26, 2014 at 11:44:57AM +0100, Malcolm Priestley wrote:
> > On 26/07/14 10:18, Guillaume CLÉMENT wrote:
> > > On Sat, Jul 26, 2014 at 10:24:30AM +0200, Guillaume CLÉMENT wrote:
> > > > Hi Malcolm,
> > > >
> > > > On Sat, Jul 26, 2014 at 12:09:49AM +0100, Malcolm Priestley wrote:
> > > > > Hi Guillaume
> > > > >
> > > > > On 25/07/14 13:47, Guillaume Clement wrote:
> > > > > > Sparse reported that the data from tagSCmdRequest is given by
> > > > > > userspace, so it should be tagged as such.
> > > > > extra is not in user space
> > > >
> > > > All right.
> > > >
> > > > This is still confusing to me because, taking the SIOCSIWGENIE ioctl as
> > > > an example, in device_main.c, we have this code:
> > > >
> > > > rc = iwctl_siwgenie(dev, NULL, &(wrq->u.data), wrq->u.data.pointer);
> > > >
> > > > Here the extra parameter is the last one, wrq->u.data.pointer.
> > > >
> > > > I was led to believe that wrq->u.data.pointer is in userspace (this was
> > > > reported by sparse actually) because the pointer field in data is
> > > > actually defined as __user.
> > > By the way, the original code (before my patch) reads:
> > >
> > > 	if ((wrq->length < 2) || (extra[1]+2 != wrq->length)) {
> > > 		ret = -EINVAL;
> > > 		goto out;
> > > 	}
> > > 	if (wrq->length > MAX_WPA_IE_LEN) {
> > > 		ret = -ENOMEM;
> > > 		goto out;
> > > 	}
> > > 	memset(pMgmt->abyWPAIE, 0, MAX_WPA_IE_LEN);
> > > 	if (copy_from_user(pMgmt->abyWPAIE, extra, wrq->length)) {
> > > 		ret = -EFAULT;
> > > 		goto out;
> > > 	}
> > >
> > > Note extra[1] and later copy_from_user(x, extra, y).
> > >
> > > If extra is not in userspace, we should not call copy_from_user, and if
> > > it is, we should not dereference it. There is definitely something fishy
> > > here.
> >
> > I got it wrong when the iw_handler is not present a standard ioctl is called
> > extra is in userspace.
> >
> > Sorry for the noise.
>
> So this patch is acceptable?
Yes, this patch is okay.


> confused,
>
> greg k-h

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