linux-kernel - Re: [PATCH v1 2/4] clone: add CLONE

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Date:   Wed, 17 Apr 2019 16:22:54 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Christian Brauner <christian@...uner.io>
Cc:     torvalds@...ux-foundation.org, viro@...iv.linux.org.uk,
        jannh@...gle.com, dhowells@...hat.com, linux-api@...r.kernel.org,
        linux-kernel@...r.kernel.org, serge@...lyn.com, luto@...nel.org,
        arnd@...db.de, ebiederm@...ssion.com, keescook@...omium.org,
        tglx@...utronix.de, mtk.manpages@...il.com,
        akpm@...ux-foundation.org, cyphar@...har.com,
        joel@...lfernandes.org, dancol@...gle.com
Subject: Re: [PATCH v1 2/4] clone: add CLONE_PIDFD

On 04/16, Christian Brauner wrote:
>
> +	if (clone_flags & CLONE_PIDFD) {
> +		retval = pidfd_create(pid, &pidfdf);
> +		if (retval < 0)
> +			goto bad_fork_free_pid;
> +		pidfd = retval;
> +	}

...

> +	if (clone_flags & CLONE_PIDFD) {
> +		fd_install(pidfd, pidfdf);
> +		put_user(pidfd, parent_tidptr);

put_user() can fail, I don't think this error should be silently ignored,
this can lead to the hard-to-trigger/debug problems.

Why can't we do put_user-with-check along with pidfd_create() above?

Oleg.