Re: [RFC PATCH v4 2/3] io_uring: add api to set / get napi configuration.

[Ammar Faizi <ammarfaizi2@gnuweeb.org>]

On 11/22/22 12:29 AM, Stefan Roesch wrote:
> +static int io_register_napi(struct io_ring_ctx *ctx, void __user *arg)
> +{
> +#ifdef CONFIG_NET_RX_BUSY_POLL
> +	const struct io_uring_napi curr = {
> +		.busy_poll_to = ctx->napi_busy_poll_to,
> +	};
> +	struct io_uring_napi *napi;
> +
> +	napi = memdup_user(arg, sizeof(*napi));
> +	if (IS_ERR(napi))
> +		return PTR_ERR(napi);
> +
> +	WRITE_ONCE(ctx->napi_busy_poll_to, napi->busy_poll_to);
> +
> +	kfree(napi);
> +
> +	if (copy_to_user(arg, &curr, sizeof(curr)))
> +		return -EFAULT;
> +
> +	return 0;

Considering:

    1) `struct io_uring_napi` is 16 bytes in size.

    2) The lifetime of `struct io_uring_napi *napi;` is brief.

There is no need to use memdup_user() and kfree(). You can place it
on the stack and use copy_from_user() instead.

-- 
Ammar Faizi