From: Greg KH <greg@kroah.com>
Subject: Re: [PATCH, RFC] random: introduce getrandom(2) system call
Date: Thu, 17 Jul 2014 12:33:30 -0700
Message-ID: <20140717193330.GB4703@kroah.com>
References: <1405588695-12014-1-git-send-email-tytso@mit.edu>
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Cc: linux-kernel@vger.kernel.org, linux-abi@vger.kernel.org,
	linux-crypto@vger.kernel.org, beck@openbsd.org
To: Theodore Ts'o <tytso@mit.edu>
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On Thu, Jul 17, 2014 at 05:18:15AM -0400, Theodore Ts'o wrote:
> +SYSCALL_DEFINE3(getrandom, char __user *, buf, size_t, count,
> +		unsigned int, flags)
> +{
> +	int r;
> +
> +	if (count > 256)
> +		return -EINVAL;
> +
> +	if (flags & GRND_RANDOM) {
> +		return _random_read(!(flags & GRND_BLOCK), buf, count);
> +	}
> +	if (flags & GRND_BLOCK) {
> +		r = wait_for_completion_interruptible(&urandom_initialized);
> +		if (r)
> +			return r;
> +	} else if (!completion_done(&urandom_initialized))
> +		return -EAGAIN;
> +	return urandom_read(NULL, buf, count, NULL);
> +}

You should fail if any other bits are set that you don't understand in
the flags value, to make it easier for newer kernels with more flags to
fail properly on old kernel releases.

thanks,

greg k-h