linux-kernel - Re: Does uaccess_kernel() work for detecting kernel thread?

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Message-ID: <20210105075731.GB30414@lst.de>
Date:   Tue, 5 Jan 2021 08:57:31 +0100
From:   Christoph Hellwig <hch@....de>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        Al Viro <viro@...iv.linux.org.uk>,
        Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@....de>,
        Kees Cook <keescook@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: Does uaccess_kernel() work for detecting kernel thread?

On Tue, Dec 22, 2020 at 11:33:58AM -0600, Eric W. Biederman wrote:
> I do wonder though if perhaps we should create a is_user_cred helper to
> detect the difference between the creds of kernel threads and the thread
> of ordinary userspace.   Which would handle io_uring that copy creds
> around and check them at a later time more cleanly.

I don't think we should as no one has a business to check this difference.
If there is a case where the creds are not correct for all access decisions
we need to fix that rather than adding hacks.