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Date:   Thu, 13 Oct 2022 19:02:09 +0200
From:   Greg KH <gregkh@linuxfoundation.org>
To:     "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc:     stable@vger.kernel.org
Subject: Re: [PATCH stable 4.9.y] random: restore O_NONBLOCK support
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On Thu, Oct 13, 2022 at 10:32:31AM -0600, Jason A. Donenfeld wrote:
> commit cd4f24ae9404fd31fc461066e57889be3b68641b upstream.
> 
> Prior to 5.6, when /dev/random was opened with O_NONBLOCK, it would
> return -EAGAIN if there was no entropy. When the pools were unified in
> 5.6, this was lost. The post 5.6 behavior of blocking until the pool is
> initialized, and ignoring O_NONBLOCK in the process, went unnoticed,
> with no reports about the regression received for two and a half years.
> However, eventually this indeed did break somebody's userspace.
> 
> So we restore the old behavior, by returning -EAGAIN if the pool is not
> initialized. Unlike the old /dev/random, this can only occur during
> early boot, after which it never blocks again.
> 
> In order to make this O_NONBLOCK behavior consistent with other
> expectations, also respect users reading with preadv2(RWF_NOWAIT) and
> similar.
> 
> Fixes: 30c08efec888 ("random: make /dev/random be almost like /dev/urandom")
> Reported-by: Guozihua <guozihua@huawei.com>
> Reported-by: Zhongguohua <zhongguohua1@huawei.com>
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> Cc: Theodore Ts'o <tytso@mit.edu>
> Cc: Andrew Lutomirski <luto@kernel.org>
> Cc: stable@vger.kernel.org
> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
> ---
>  drivers/char/random.c | 4 ++++
>  1 file changed, 4 insertions(+)

Now queued up, thanks.

greg k-h