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

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

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?

confused,

greg k-h