netdev - Re: [PATCH v6 6/7] seccomp: Introduce addfd ioctl to seccomp user notifier

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Message-ID: <202007082307.EB5BAD3A0@keescook>
Date:   Wed, 8 Jul 2020 23:12:02 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Christian Brauner <christian.brauner@...ntu.com>
Cc:     linux-kernel@...r.kernel.org, Sargun Dhillon <sargun@...gun.me>,
        Matt Denton <mpdenton@...gle.com>,
        Christian Brauner <christian@...uner.io>,
        Tycho Andersen <tycho@...ho.ws>,
        David Laight <David.Laight@...LAB.COM>,
        Christoph Hellwig <hch@....de>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Aleksa Sarai <cyphar@...har.com>, Jann Horn <jannh@...gle.com>,
        Chris Palmer <palmer@...gle.com>,
        Robert Sesek <rsesek@...gle.com>,
        Giuseppe Scrivano <gscrivan@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andy Lutomirski <luto@...capital.net>,
        Will Drewry <wad@...omium.org>, Shuah Khan <shuah@...nel.org>,
        netdev@...r.kernel.org, containers@...ts.linux-foundation.org,
        linux-api@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v6 6/7] seccomp: Introduce addfd ioctl to seccomp user
 notifier

On Tue, Jul 07, 2020 at 03:30:49PM +0200, Christian Brauner wrote:
> Hm, maybe change that description to sm like:
> 
> [...]

Cool, yeah. Thanks! I've tweaked it a little more

> > +	/* 24 is original sizeof(struct seccomp_notif_addfd) */
> > +	if (size < 24 || size >= PAGE_SIZE)
> > +		return -EINVAL;
> 
> Hm, so maybe add the following:
> 
> #define SECCOMP_NOTIFY_ADDFD_VER0 24
> #define SECCOMP_NOTIFY_ADDFD_LATEST SECCOMP_NOTIFY_ADDFD_VER0
> 
> and then place:
> 
> BUILD_BUG_ON(sizeof(struct seccomp_notify_addfd) < SECCOMP_NOTIFY_ADDFD_VER0);
> BUILD_BUG_ON(sizeof(struct open_how) != SECCOMP_NOTIFY_ADDFD_LATEST);

Yes, good idea (BTW, did the EA syscall docs land?)

I've made these SECCOMP_NOTIFY_ADDFD_SIZE_* to match your examples below
(i.e.  I added "SIZE" to what you suggested above).

> somewhere which is what we do for clone3(), openat2() and others to
> catch build-time nonsense.
> 
> include/uapi/linux/perf_event.h:#define PERF_ATTR_SIZE_VER0     64      /* sizeof first published struct */
> include/uapi/linux/sched.h:#define CLONE_ARGS_SIZE_VER0 64 /* sizeof first published struct */
> include/uapi/linux/sched/types.h:#define SCHED_ATTR_SIZE_VER0   48      /* sizeof first published struct */
> include/linux/fcntl.h:#define OPEN_HOW_SIZE_VER0        24 /* sizeof first published struct */
> include/linux/fcntl.h:#define OPEN_HOW_SIZE_LATEST      OPEN_HOW_SIZE_VER0

The ..._SIZE_VER0 and ...LATEST stuff doesn't seem useful to export via
UAPI. Above, 2 of the 3 export to uapi. Is there a specific rationale
for which should and which shouldn't?

> > +#undef EA_IOCTL
> 
> Why is this undefed? :)

It was defined "in" a function, so I like to mimic function visibility.
But you're right; there's no reason to undef it.

-- 
Kees Cook