linux-kernel - Re: [PATCH v3 2/4] bus: fsl-mc: add fsl-mc userspace support

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Message-ID: <20181120164850.GC27531@kroah.com>
Date:   Tue, 20 Nov 2018 17:48:50 +0100
From:   "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
To:     Ioana Ciornei <ioana.ciornei@....com>
Cc:     Laurentiu Tudor <laurentiu.tudor@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev-owner@...r.kernel.org" <netdev-owner@...r.kernel.org>,
        Ioana Ciocoi Radulescu <ruxandra.radulescu@....com>,
        Horia Geanta <horia.geanta@....com>,
        Leo Li <leoyang.li@....com>
Subject: Re: [PATCH v3 2/4] bus: fsl-mc: add fsl-mc userspace support

On Tue, Nov 20, 2018 at 03:39:45PM +0000, Ioana Ciornei wrote:
> +static int fsl_mc_uapi_send_command(unsigned long arg,
> +				    struct fsl_mc_io *mc_io)
> +{
> +	struct fsl_mc_command mc_cmd;
> +	int error;
> +
> +	error = copy_from_user(&mc_cmd, (void __user *)arg, sizeof(mc_cmd));
> +	if (error)
> +		return -EFAULT;
> +
> +	error = mc_send_command(mc_io, &mc_cmd);
> +	if (error)
> +		return error;
> +
> +	error = copy_to_user((void __user *)arg, &mc_cmd, sizeof(mc_cmd));
> +	if (error)
> +		return -EFAULT;
> +
> +	return 0;
> +}

I know you said that "the firmware will properly verify the command"
already, but given that I used to be a firmware developer a long time
ago, I can almost guarantee that this will cause problems in the future.

Want to make a friendly bet about this?

What is the odds that your firmware api/interface has been properly
fuzzed such that all possible combinations of bad commands will really
not do horrible things to the hardware/system?

Are you all willing to bet the system intregrity on this?  If so, ok,
it's your systems :)

Personally, I think you need to add a "known whitelist" and do some sort
of sanity checking here.

thanks,

greg k-h