netdev - Re: [PATCH 0/2] Use __scm_install

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Date:   Wed, 10 Jun 2020 10:03:03 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Christian Brauner <christian.brauner@...ntu.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Christoph Hellwig <hch@....de>,
        Christian Brauner <christian@...uner.io>,
        Sargun Dhillon <sargun@...gun.me>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] Use __scm_install_fd() more widely

On Wed, Jun 10, 2020 at 11:47:35AM +0200, Christian Brauner wrote:
> On Tue, Jun 09, 2020 at 09:52:12PM -0700, Kees Cook wrote:
> > Hi,
> > 
> > This extends the recent work hch did for scm_detach_fds(), and updates
> > the compat path as well, fixing bugs in the process. Additionally,
> > an effectively incomplete and open-coded __scm_install_fd() is fixed
> > in pidfd_getfd().
> 
> Since __scm_detach_fds() becomes something that is available outside of
> net/* should we provide a static inline wrapper under a different name? The
> "socket-level control message" prefix seems a bit odd in pidfd_getfd()
> and - once we make use of it there - seccomp.
> 
> I'd suggest we do:
> 
> static inline int fd_install_received(struct file *file, unsigned int flags)
> {
> 	return __scm_install_fd(file, NULL, flags);
> }
> 
> which can be called in pidfd_getfd() and once we have other callers that
> want the additional put_user() (e.g. seccomp_ in there we simply add:
> 
> static inline fd_install_user(struct file *file, unsigned int flags, int __user *ufd)
> {
> 	return __scm_install_fd(file, ufd, flags);
> }
> 
> and seems the wrappers both could happily live in the fs part of the world?

I combined your and Sargun's suggestions. (It can't live in any more
net/core/scm.c in the case of CONFIG_NET=n, but the wrappers make the
changes much nicer looking.)

https://git.kernel.org/pub/scm/linux/kernel/git/kees/linux.git/log/?h=devel/seccomp/addfd/v3.2

If 0-day doesn't kick anything back on this tree, I'll resend the
series...

-- 
Kees Cook