Re: [PATCH v3] leds: Introduce userspace leds driver

[Jacek Anaszewski]

On 09/16/2016 07:50 AM, Pavel Machek wrote:
> Hi!
>
> > > > > > +    if (copy_from_user(&udev->user_dev, buffer,
> > > > > > +               sizeof(struct uleds_user_dev))) {
> > > > > > +        ret = -EFAULT;
> > > > > > +        goto out;
> > > > > > +    }
> > > > > > +
> > > > > > +    if (!udev->user_dev.name[0]) {
> > > > > > +        ret = -EINVAL;
> > > > > > +        goto out;
> > > > > > +    }
> > > > > > +
> > > > > > +    ret = led_classdev_register(NULL, &udev->led_cdev);
> > > > > > +    if (ret < 0)
> > > > > > +        goto out;
> > > >
> > > > No sanity checking on the name -> probably a security hole. Do not
> > > > push this upstream before this is fixed.
> >
> > If this is a serious security issue, then you should also raise an issue
> > with input maintainers because this is the extent of sanity checking for
> > uinput device names as well.
>
> I guess that should be fixed. But lets not add new ones.
>
> > I must confess that I am no security expert, so unless you can give specific
> > examples of what potential threats are, I will not be able to guess what I
> > need to do to fix it.
> >
> > After some digging around the kernel, I don't see many instances of
> > validating device node names. The best I have found so far comes from
> > create_entry() in binfmt_misc.c
> >
> > 	if (!e->name[0] ||
> > 	    !strcmp(e->name, ".") ||
> > 	    !strcmp(e->name, "..") ||
> > 	    strchr(e->name, '/'))
> > 		goto einval;
> >
> > Would something like this be a sufficient sanity check? I suppose we could
> > also check for non-printing characters, but I don't think ignoring them
> > would be a security issue.
>
> That would be minimum, yes. I guess it would be better/easier to just
> limit the names to [a-zA-Z:-_0-9]*?

Right, and we also could check if there are no more then two ":"
characters in the name.

--
Best regards,
Jacek Anaszewski