IO-Uring Archive on lore.kernel.org
 help / color / Atom feed
From: Jens Axboe <axboe@kernel.dk>
To: Stefan Metzmacher <metze@samba.org>, io-uring@vger.kernel.org
Cc: linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk
Subject: Re: [PATCH 3/6] io_uring: add support for IORING_OP_OPENAT
Date: Wed, 8 Jan 2020 16:05:59 -0700
Message-ID: <0b8a0f70-c2de-1b1c-28d4-5c578a3534eb@kernel.dk> (raw)
In-Reply-To: <a0f1b3a0-9827-b3e1-da0c-a2b71151fd4e@samba.org>

On 1/8/20 4:03 PM, Stefan Metzmacher wrote:
> Am 08.01.20 um 23:53 schrieb Jens Axboe:
>> On 1/8/20 10:04 AM, Stefan Metzmacher wrote:
>>> Am 08.01.20 um 17:40 schrieb Jens Axboe:
>>>> On 1/8/20 9:32 AM, Stefan Metzmacher wrote:
>>>>> Am 08.01.20 um 17:20 schrieb Jens Axboe:
>>>>>> On 1/8/20 6:05 AM, Stefan Metzmacher wrote:
>>>>>>> Hi Jens,
>>>>>>>
>>>>>>>> This works just like openat(2), except it can be performed async. For
>>>>>>>> the normal case of a non-blocking path lookup this will complete
>>>>>>>> inline. If we have to do IO to perform the open, it'll be done from
>>>>>>>> async context.
>>>>>>>
>>>>>>> Did you already thought about the credentials being used for the async
>>>>>>> open? The application could call setuid() and similar calls to change
>>>>>>> the credentials of the userspace process/threads. In order for
>>>>>>> applications like samba to use this async openat, it would be required
>>>>>>> to specify the credentials for each open, as we have to multiplex
>>>>>>> requests from multiple user sessions in one process.
>>>>>>>
>>>>>>> This applies to non-fd based syscall. Also for an async connect
>>>>>>> to a unix domain socket.
>>>>>>>
>>>>>>> Do you have comments on this?
>>>>>>
>>>>>> The open works like any of the other commands, it inherits the
>>>>>> credentials that the ring was setup with. Same with the memory context,
>>>>>> file table, etc. There's currently no way to have multiple personalities
>>>>>> within a single ring.
>>>>>
>>>>> Ah, it's user = get_uid(current_user()); and ctx->user = user in
>>>>> io_uring_create(), right?
>>>>
>>>> That's just for the accounting, it's the:
>>>>
>>>> ctx->creds = get_current_cred();
>>>
>>> Ok, I just looked at an old checkout.
>>>
>>> In kernel-dk-block/for-5.6/io_uring-vfs I see this only used in
>>> the async processing. Does a non-blocking openat also use ctx->creds?
>>
>> There's basically two sets here - one set is in the ring, and the other
>> is the identity that the async thread (briefly) assumes if we have to go
>> async. Right now they are the same thing, and hence we don't need to
>> play any tricks off the system call submitting SQEs to assume any other
>> identity than the one we have.
> 
> I see two cases using it io_sq_thread() and
> io_wq_create()->io_worker_handle_work() call override_creds().
> 
> But aren't non-blocking syscall executed in the context of the thread
> calling io_uring_enter()->io_submit_sqes()?
> In only see some magic around ctx->sqo_mm for that case, but ctx->creds
> doesn't seem to be used in that case. And my design would require that.

For now, the sq thread (which is used if you use IORING_SETUP_SQPOLL)
currently requires fixed files, so it can't be used with open at the
moment anyway. But if/when enabled, it'll assume the same credentials
as the async context and syscall path.

-- 
Jens Axboe


  reply index

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-07 17:00 [PATCHSET v2 0/6] io_uring: add support for open/close Jens Axboe
2020-01-07 17:00 ` [PATCH 1/6] fs: add namei support for doing a non-blocking path lookup Jens Axboe
2020-01-25 13:15   ` Jeff Layton
2020-01-07 17:00 ` [PATCH 2/6] fs: make build_open_flags() available internally Jens Axboe
2020-01-07 17:00 ` [PATCH 3/6] io_uring: add support for IORING_OP_OPENAT Jens Axboe
2020-01-08 13:05   ` Stefan Metzmacher
2020-01-08 16:20     ` Jens Axboe
2020-01-08 16:32       ` Stefan Metzmacher
2020-01-08 16:40         ` Jens Axboe
2020-01-08 17:04           ` Stefan Metzmacher
2020-01-08 22:53             ` Jens Axboe
2020-01-08 23:03               ` Stefan Metzmacher
2020-01-08 23:05                 ` Jens Axboe [this message]
2020-01-08 23:11                   ` Stefan Metzmacher
2020-01-08 23:22                     ` Jens Axboe
2020-01-09 10:40                       ` Stefan Metzmacher
2020-01-09 21:31                         ` Jens Axboe
2020-01-16 22:42                           ` Stefan Metzmacher
2020-01-17  0:16                             ` Jens Axboe
2020-01-07 17:00 ` [PATCH 4/6] fs: move filp_close() outside of __close_fd_get_file() Jens Axboe
2020-01-07 17:00 ` [PATCH 5/6] io-wq: add support for uncancellable work Jens Axboe
2020-01-07 17:00 ` [PATCH 6/6] io_uring: add support for IORING_OP_CLOSE Jens Axboe
2020-01-08 21:17 ` [PATCHSET v2 0/6] io_uring: add support for open/close Stefan Metzmacher
2020-01-08 22:57   ` Jens Axboe
2020-01-08 23:05     ` Stefan Metzmacher
2020-01-09  1:02       ` Jens Axboe
2020-01-09  2:03         ` Jens Axboe
2020-01-16 22:50           ` Stefan Metzmacher
2020-01-17  0:18             ` Jens Axboe
2020-01-20 12:15               ` Stefan Metzmacher
2020-01-20 13:04                 ` Pavel Begunkov
2020-01-17  0:44             ` Colin Walters
2020-01-17  0:51               ` Jens Axboe
2020-01-17  9:32               ` Pavel Begunkov
2020-01-17 15:21                 ` Jens Axboe
2020-01-17 22:27                   ` Pavel Begunkov
2020-01-17 22:36                     ` Jens Axboe

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=0b8a0f70-c2de-1b1c-28d4-5c578a3534eb@kernel.dk \
    --to=axboe@kernel.dk \
    --cc=io-uring@vger.kernel.org \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=metze@samba.org \
    --cc=viro@zeniv.linux.org.uk \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

IO-Uring Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/io-uring/0 io-uring/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 io-uring io-uring/ https://lore.kernel.org/io-uring \
		io-uring@vger.kernel.org
	public-inbox-index io-uring

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.io-uring


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git