Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH] fs/io_uring: fix O_PATH fds in openat, openat2, statx
To:     Al Viro <viro@zeniv.linux.org.uk>
Cc:     Max Kellermann <mk@cm4all.com>, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org, stable@vger.kernel.org
References: <20200507185725.15840-1-mk@cm4all.com>
 <20200507190131.GF23230@ZenIV.linux.org.uk>
 <4cac0e53-656c-50f0-3766-ae3cc6c0310a@kernel.dk>
 <20200507192903.GG23230@ZenIV.linux.org.uk>
 <8e3c88cc-027b-4f90-b4f8-a20d11d35c4b@kernel.dk>
 <20200507220637.GH23230@ZenIV.linux.org.uk>
 <283c8edb-fea2-5192-f1d6-3cc57815b1e2@kernel.dk>
 <20200507224447.GI23230@ZenIV.linux.org.uk>
 <e16125f2-c3ec-f029-c607-19bede54fa17@kernel.dk>
 <20200507233132.GJ23230@ZenIV.linux.org.uk>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <629de3b6-cf80-fe37-1dde-7f0464da0a04@kernel.dk>
Date:   Thu, 7 May 2020 20:28:10 -0600
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.7.0
MIME-Version: 1.0
In-Reply-To: <20200507233132.GJ23230@ZenIV.linux.org.uk>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 5/7/20 5:31 PM, Al Viro wrote:
> On Thu, May 07, 2020 at 05:03:17PM -0600, Jens Axboe wrote:
>> On 5/7/20 4:44 PM, Al Viro wrote:
>>> On Thu, May 07, 2020 at 04:25:24PM -0600, Jens Axboe wrote:
>>>
>>>>  static int io_close(struct io_kiocb *req, bool force_nonblock)
>>>>  {
>>>> +	struct files_struct *files = current->files;
>>>>  	int ret;
>>>>  
>>>>  	req->close.put_file = NULL;
>>>> -	ret = __close_fd_get_file(req->close.fd, &req->close.put_file);
>>>> +	spin_lock(&files->file_lock);
>>>> +	if (req->file->f_op == &io_uring_fops ||
>>>> +	    req->close.fd == req->ctx->ring_fd) {
>>>> +		spin_unlock(&files->file_lock);
>>>> +		return -EBADF;
>>>> +	}
>>>> +
>>>> +	ret = __close_fd_get_file_locked(files, req->close.fd,
>>>> +						&req->close.put_file);
>>>
>>> Pointless.  By that point req->file might have nothing in common with
>>> anything in any descriptor table.
>>
>> How about the below then? Stop using req->file, defer the lookup until
>> we're in the handler instead. Not sure the 'fd' check makes sense
>> at this point, but at least we should be consistent in terms of
>> once we lookup the file and check the f_op.
> 
> Actually, what _is_ the reason for that check?  Note, BTW, that if the
> file in question happens to be an AF_UNIX socket, closing it will
> close all references held in SCM_RIGHTS datagrams sitting in its queue,
> which might very well include io_uring files.
> 
> IOW, if tries to avoid something really unpleasant, it's not enough.
> And if it doesn't, then what is it for?

Maybe there is no issue at all, the point was obviously to not have
io_uring close itself. But we might just need an ordering of the
fput vs put_request to make that just fine. Let me experiment a bit
and see what's going on.

-- 
Jens Axboe