Received-SPF: pass (google.com: domain of linux-crypto-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <29c4a3ec-f23f-f17f-da49-7d79ad88e284@huawei.com>
Date:   Tue, 26 Jul 2022 15:43:31 +0800
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101
 Thunderbird/91.8.0
Subject: Re: Inquiry about the removal of flag O_NONBLOCK on /dev/random
Content-Language: en-US
To:     "Jason A. Donenfeld" <Jason@zx2c4.com>,
        Eric Biggers <ebiggers@kernel.org>
CC:     <linux-crypto@vger.kernel.org>, <luto@kernel.org>, <tytso@mit.edu>
References: <13e1fa9d-4df8-1a99-ca22-d9d655f2d023@huawei.com>
 <YtaPJPkewin5uWdn@zx2c4.com>
 <b9cb514c-30ed-0b8b-5d54-75001e07bd36@huawei.com>
 <YtjREZMzuppTJHeR@sol.localdomain>
 <a93995db-a738-8e4f-68f2-42d7efd3c77d@huawei.com>
 <Ytj3RnGtWqg18bxO@sol.localdomain> <YtksefZvcFiugeC1@zx2c4.com>
From:   "Guozihua (Scott)" <guozihua@huawei.com>
In-Reply-To: <YtksefZvcFiugeC1@zx2c4.com>
Content-Type: text/plain; charset="UTF-8"; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 2022/7/21 18:37, Jason A. Donenfeld wrote:
> Hi Guozihua,
> 
> On Wed, Jul 20, 2022 at 11:50:46PM -0700, Eric Biggers wrote:
>> On Thu, Jul 21, 2022 at 02:44:54PM +0800, Guozihua (Scott) wrote:
>>>
>>> Hi Eric
>>>
>>> We have a userspace program that starts pretty early in the boot process and
>>> it tries to fetch random bits from /dev/random with O_NONBLOCK, if that
>>> returns -EAGAIN, it turns to /dev/urandom. Is this a correct handling of
>>> -EAGAIN? Or this is not one of the intended use case of O_NONBLOCK?
>>
>> That doesn't make any sense; you should just use /dev/urandom unconditionally.
> 
> What Eric said: this flow doesn't really make sense. Why not use
> /dev/urandom unconditionally or getrandom(GRND_INSECURE)?
> 
> But also I have to wonder: you wrote '-EAGAIN' but usually userspace
> checks errno==EAGAIN, a positive value. That makes me wonder whether you
> wrote your email with your code is open. So I just wanted to triple
> check that what you've described is actually what the code is doing,
> just in case there's some ambiguity.
> 
> I'm just trying to find out what this code is and where it is to assess
> whether we change the userspace behavior again, given that this has been
> sitting for several years now.
> 
> Jason
> .

Hi Jason, Eric and Theodore,

Thanks for all the comments on this inquiry. Does the community has any 
channel to publishes changes like these? And will the man pages get 
updated? If so, are there any time frame?

-- 
Best
GUO Zihua