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From: Stefan Metzmacher <[email protected]>
To: Jens Axboe <[email protected]>
Cc: io-uring <[email protected]>
Subject: Re: [PATCH] io_uring/net: save msghdr->msg_control for retries
Date: Mon, 19 Jun 2023 15:09:38 +0200	[thread overview]
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>

Am 19.06.23 um 15:05 schrieb Jens Axboe:
> On 6/19/23 3:57?AM, Stefan Metzmacher wrote:
>> Hi Jens,
>>
>>> If the application sets ->msg_control and we have to later retry this
>>> command, or if it got queued with IOSQE_ASYNC to begin with, then we
>>> need to retain the original msg_control value. This is due to the net
>>> stack overwriting this field with an in-kernel pointer, to copy it
>>> in. Hitting that path for the second time will now fail the copy from
>>> user, as it's attempting to copy from a non-user address.
>>
>> I'm not 100% sure about the impact of this change.
>>
>> But I think the logic we need is that only the
>> first __sys_sendmsg_sock() that returns > 0 should
>> see msg_control. A retry because of MSG_WAITALL should
>> clear msg_control[len] for a follow up __sys_sendmsg_sock().
>> And I fear the patch below would not clear it...
>>
>> Otherwise the receiver/socket-layer will get the same msg_control twice,
>> which is unexpected.
> 
> Yes agree, if we do transfer some (but not all) data and WAITALL is set,
> it should get cleared. I'll post a patch for that.

Thanks!

> Note that it was also broken before, just differently broken. The most
> likely outcome here was a full retry and now getting -EFAULT.

Yes, I can see that it was broken before...

metze

  reply	other threads:[~2023-06-19 13:09 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-06-12 19:56 [PATCH] io_uring/net: save msghdr->msg_control for retries Jens Axboe
2023-06-19  9:57 ` Stefan Metzmacher
2023-06-19 13:05   ` Jens Axboe
2023-06-19 13:09     ` Stefan Metzmacher [this message]
2023-06-19 13:27       ` Stefan Metzmacher
2023-06-19 14:38         ` Jens Axboe
2023-06-19 14:40           ` Stefan Metzmacher
2023-06-19 14:40             ` Jens Axboe

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