linux-kernel - Re: [PATCH v4 0/3] random: convert to using iters, for Al Viro

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Message-ID: <7e78d6a7-1cc3-2408-fe91-0329f5020e77@kernel.dk>
Date:   Fri, 20 May 2022 09:53:30 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>,
        Theodore Ts'o <tytso@....edu>, Christoph Hellwig <hch@....de>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 0/3] random: convert to using iters, for Al Viro

On 5/20/22 9:47 AM, Al Viro wrote:
> On Fri, May 20, 2022 at 09:34:46AM -0600, Jens Axboe wrote:
> 
>> I'm very sure, otherwise we're just accepting that we're breaking real
>> world applications.
> 
> "Breaking" as in "it used to work with earlier kernels, doesn't work with
> recent ones"?  Details, please...

Yes, as in exactly that. This is what drove this addition of
->read_iter() for urandom. See commit:

ommit 36e2c7421f02a22f71c9283e55fdb672a9eb58e7
Author: Christoph Hellwig <hch@....de>
Date:   Thu Sep 3 16:22:34 2020 +0200

    fs: don't allow splice read/write without explicit ops

related to the set_fs() changes, and now go look for any commit that
has:

Fixes: 36e2c7421f02 ("fs: don't allow splice read/write without explicit ops")

in it and see that this isn't an isolated incident at all.

tldr - splice from /dev/urandom used to work, and I recently got a
report internally on an application that broke on upgrade from 5.6 to
5.12 exactly because it now just just -EINVAL's instead.

-- 
Jens Axboe