linux-kernel - Re: [PATCH 4/5] seccomp: Add SECCOMP_ADDFD_FLAG

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Date:   Mon, 25 May 2020 23:08:19 -0700
From:   Sargun Dhillon <sargun@...gun.me>
To:     Christian Brauner <christian.brauner@...ntu.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linux Containers <containers@...ts.linux-foundation.org>,
        Linux API <linux-api@...r.kernel.org>,
        Tycho Andersen <tycho@...ho.ws>,
        Kees Cook <keescook@...omium.org>,
        Aleksa Sarai <cyphar@...har.com>,
        Jeffrey Vander Stoep <jeffv@...gle.com>,
        Jann Horn <jannh@...gle.com>, Robert Sesek <rsesek@...gle.com>,
        Chris Palmer <palmer@...gle.com>,
        Matt Denton <mpdenton@...gle.com>,
        Kees Cook <keescook@...gle.com>
Subject: Re: [PATCH 4/5] seccomp: Add SECCOMP_ADDFD_FLAG_MOVE flag to add fd ioctl

> > + * they are created in. Specifcally, sockets, and their interactions with the
> > + * net_cls and net_prio cgroup v1 controllers. This "moves" the file descriptor
> > + * so that it takes on the cgroup controller's configuration in the process
> > + * that the file descriptor is being added to.
> > + */
> > +#define SECCOMP_ADDFD_FLAG_MOVE              (1UL << 1)
>
> I'm not happy about the name because "moving" has much more to do with
> transferring ownership than what we are doing here. After a "move" the
> fd shouldn't be valid anymore. But that might just be my thinking.
>
> But why make this opt-in and not do it exactly like when you send around
> fds and make this mandatory?

Based upon Tycho's comments in an offline thread, I'm going to make
this the default
(setting the cgroup metadata) to mirror what SCM_RIGHTS does, and then
if we come
up with a good use case where we need to preserve *cgroup v1*
metadata, then we can
add an opt-out flag in the future.