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

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Date:   Wed, 10 Jun 2020 11:47:35 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Kees Cook <keescook@...omium.org>
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 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?

Christian