linux-kernel - Re: [PATCH v2 2/3] seccomp: Introduce addfd ioctl to seccomp user notifier

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Date:   Sat, 30 May 2020 15:08:37 +0100
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Kees Cook <keescook@...omium.org>
Cc:     Sargun Dhillon <sargun@...gun.me>, christian.brauner@...ntu.com,
        containers@...ts.linux-foundation.org, cyphar@...har.com,
        jannh@...gle.com, jeffv@...gle.com, linux-api@...r.kernel.org,
        linux-kernel@...r.kernel.org, palmer@...gle.com, rsesek@...gle.com,
        tycho@...ho.ws, Matt Denton <mpdenton@...gle.com>
Subject: Re: [PATCH v2 2/3] seccomp: Introduce addfd ioctl to seccomp user
 notifier

On Fri, May 29, 2020 at 07:43:10PM -0700, Kees Cook wrote:

> Can anyone clarify the expected failure mode from SCM_RIGHTS? Can we
> move the put_user() after instead? I think cleanup would just be:
> replace_fd(fd, NULL, 0)

Bollocks.

Repeat after me: descriptor tables can be shared.  There is no
"cleanup" after you've put something there.  If you do not get
it, you have no business messing with any of this stuff.