Re: [PATCH v2] io_uring/net: disable partial retries for recvmsg with cmsg

[Stefan Metzmacher <metze@samba.org>]

Am 20.06.23 um 15:19 schrieb Jens Axboe:
> We cannot sanely handle partial retries for recvmsg if we have cmsg
> attached. If we don't, then we'd just be overwriting the initial cmsg
> header on retries. Alternatively we could increment and handle this
> appropriately, but it doesn't seem worth the complication.
> 
> Move the MSG_WAITALL check into the non-multishot case while at it,
> since MSG_WAITALL is explicitly disabled for multishot anyway.
> 
> Link: https://lore.kernel.org/io-uring/0b0d4411-c8fd-4272-770b-e030af6919a0@kernel.dk/
> Cc: stable@vger.kernel.org # 5.10+
> Reported-by: Stefan Metzmacher <metze@samba.org>
> Signed-off-by: Jens Axboe <axboe@kernel.dk>

Also Reviewed-by: Stefan Metzmacher <metze@samba.org>

> ---
> 
> v2: correct msg_controllen check and move into non-mshot branch
> 
>   io_uring/net.c | 11 +++++++----
>   1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/io_uring/net.c b/io_uring/net.c
> index c0924ab1ea11..2bc2cb2f4d6c 100644
> --- a/io_uring/net.c
> +++ b/io_uring/net.c
> @@ -789,16 +789,19 @@ int io_recvmsg(struct io_kiocb *req, unsigned int issue_flags)
>   	flags = sr->msg_flags;
>   	if (force_nonblock)
>   		flags |= MSG_DONTWAIT;
> -	if (flags & MSG_WAITALL)
> -		min_ret = iov_iter_count(&kmsg->msg.msg_iter);
>   
>   	kmsg->msg.msg_get_inq = 1;
> -	if (req->flags & REQ_F_APOLL_MULTISHOT)
> +	if (req->flags & REQ_F_APOLL_MULTISHOT) {
>   		ret = io_recvmsg_multishot(sock, sr, kmsg, flags,
>   					   &mshot_finished);
> -	else
> +	} else {
> +		/* disable partial retry for recvmsg with cmsg attached */
> +		if (flags & MSG_WAITALL && !kmsg->msg.msg_controllen)
> +			min_ret = iov_iter_count(&kmsg->msg.msg_iter);
> +
>   		ret = __sys_recvmsg_sock(sock, &kmsg->msg, sr->umsg,
>   					 kmsg->uaddr, flags);
> +	}
>   
>   	if (ret < min_ret) {
>   		if (ret == -EAGAIN && force_nonblock) {