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From:   "Jason A. Donenfeld" <Jason@zx2c4.com>
Date:   Fri, 8 Apr 2022 12:33:47 +0200
Message-ID: <CAHmME9qZ4HjG_qL2qb=bUn95rUmd_F8bUnzD=Ht2MMAjuH0CFg@mail.gmail.com>
Subject: Re: [PATCH v2] random: allow partial reads if later user copies fail
To:     David Laight <David.Laight@aculab.com>
Cc:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "torvalds@linux-foundation.org" <torvalds@linux-foundation.org>,
        "tytso@mit.edu" <tytso@mit.edu>,
        "sultan@kerneltoast.com" <sultan@kerneltoast.com>,
        Jann Horn <jannh@google.com>
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Hi David,

On 4/8/22, David Laight <David.Laight@aculab.com> wrote:
> From: Jason A. Donenfeld
>> Sent: 08 April 2022 00:36
>>
>> Rather than failing entirely if a copy_to_user() fails at some point,
>> instead we should return a partial read for the amount that succeeded
>> prior, unless none succeeded at all, in which case we return -EFAULT as
>> before.
>
> I think you now return -EFAULT for a zero length read.

The diff context doesn't show it, but the first line of the function
is `if (!nbytes) return 0;`, before various other bits of work are
done.

Jason