linux-kernel - Re: [PATCH v3] leds: Introduce userspace leds driver

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Date:   Fri, 16 Sep 2016 09:07:45 +0200
From:   Jacek Anaszewski <j.anaszewski@...sung.com>
To:     Pavel Machek <pavel@....cz>, David Lechner <david@...hnology.com>
Cc:     Richard Purdie <rpurdie@...ys.net>, linux-kernel@...r.kernel.org,
        linux-leds@...r.kernel.org, Marcel Holtmann <marcel@...tmann.org>
Subject: Re: [PATCH v3] leds: Introduce userspace leds driver

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