linux-kernel - Re: [rfc] fcntl: Add F_GETOWNER

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Message-ID: <20120326164347.GA24394@redhat.com>
Date:	Mon, 26 Mar 2012 18:43:47 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Cyrill Gorcunov <gorcunov@...nvz.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Pavel Emelyanov <xemul@...allels.com>
Subject: Re: [rfc] fcntl: Add F_GETOWNER_UIDS option

On 03/26, Cyrill Gorcunov wrote:
>
> +#ifdef CONFIG_CHECKPOINT_RESTORE
> +static int f_getowner_uids(struct file *filp, unsigned long arg)
> +{
> +	struct user_namespace *user_ns = current_user_ns();
> +	const struct cred *cred = current_cred();
> +	uid_t * __user dst = (void * __user)arg;
> +	uid_t src[2];
> +	int err;
> +
> +	read_lock(&filp->f_owner.lock);
> +	src[0] = filp->f_owner.uid;
> +	src[1] = filp->f_owner.euid;
> +	read_unlock(&filp->f_owner.lock);
> +
> +	src[0] = user_ns_map_uid(user_ns, cred, src[0]);
> +	src[1] = user_ns_map_uid(user_ns, cred, src[1]);

Why?

In this case user_ns_map_uid() is "nop", it should always return
the last arg, no?

Oleg.

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