linux-kernel - Re: [PATCH 1/2] random: convert to using fops->read

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Date:   Fri, 20 May 2022 03:11:06 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     tytso@....edu, Jason@...c4.com, hch@....de,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] random: convert to using fops->read_iter()

On Thu, May 19, 2022 at 05:31:36PM -0600, Jens Axboe wrote:

> @@ -418,25 +419,23 @@ static ssize_t get_random_bytes_user(void __user *ubuf, size_t len)
>  	 * the user directly.
>  	 */
>  	if (len <= CHACHA_KEY_SIZE) {
> -		ret = len - copy_to_user(ubuf, &chacha_state[4], len);
> +		ret = copy_to_iter(&chacha_state[4], len, to);
>  		goto out_zero_chacha;
>  	}
>  
>  	for (;;) {
> +		size_t copied;
> +
>  		chacha20_block(chacha_state, output);
>  		if (unlikely(chacha_state[12] == 0))
>  			++chacha_state[13];
>  
>  		block_len = min_t(size_t, len, CHACHA_BLOCK_SIZE);
> -		left = copy_to_user(ubuf, output, block_len);
> -		if (left) {
> -			ret += block_len - left;
> +		copied = copy_to_iter(output, block_len, to);
> +		ret += copied;
> +		if (copied != block_len)
>  			break;
> -		}

		copied = copy_to_iter(output, CHACHA_BLOCK_SIZE, to);
		ret += copied;
		if (copied != CHACHA_BLOCK_SIZE) {
			if (!ret)
				ret = -EFAULT;
			break;
		}
	}

>  SYSCALL_DEFINE3(getrandom, char __user *, ubuf, size_t, len, unsigned int, flags)
>  {
> +	struct iovec iov = { .iov_base = ubuf };
> +	struct iov_iter iter;

	import_single_range(READ, ubuf, len, &iov, &iter)

(note, BTW, that this'll cap len)