linux-kernel - RE: [PATCH v4 03/11] fs: Add fd_install_received() wrapper for __fd_install

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Message-ID: <6de12195ec3244b99e6026b4b46e5be2@AcuMS.aculab.com>
Date:   Wed, 17 Jun 2020 15:35:20 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Kees Cook' <keescook@...omium.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Sargun Dhillon <sargun@...gun.me>,
        Christian Brauner <christian@...uner.io>,
        "David S. Miller" <davem@...emloft.net>,
        "Christoph Hellwig" <hch@....de>, Tycho Andersen <tycho@...ho.ws>,
        Jakub Kicinski <kuba@...nel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Aleksa Sarai <cyphar@...har.com>,
        Matt Denton <mpdenton@...gle.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" <netdev@...r.kernel.org>,
        "containers@...ts.linux-foundation.org" 
        <containers@...ts.linux-foundation.org>,
        "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>
Subject: RE: [PATCH v4 03/11] fs: Add fd_install_received() wrapper for
 __fd_install_received()

From: Kees Cook
> Sent: 16 June 2020 04:25
> 
> For both pidfd and seccomp, the __user pointer is not used. Update
> __fd_install_received() to make writing to ufd optional. (ufd
> itself cannot checked for NULL because this changes the SCM_RIGHTS
> interface behavior.) In these cases, the new fd needs to be returned
> on success.  Update the existing callers to handle it. Add new wrapper
> fd_install_received() for pidfd and seccomp that does not use the ufd
> argument.
...> 
>  static inline int fd_install_received_user(struct file *file, int __user *ufd,
>  					   unsigned int o_flags)
>  {
> -	return __fd_install_received(file, ufd, o_flags);
> +	return __fd_install_received(file, true, ufd, o_flags);
> +}

Can you get rid of the 'return user' parameter by adding
	if (!ufd) return -EFAULT;
to the above wrapper, then checking for NULL in the function?

Or does that do the wrong horrid things in the fail path?

	David

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