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

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Message-ID: <20120326183330.GM19395@moon>
Date:	Mon, 26 Mar 2012 22:33:30 +0400
From:	Cyrill Gorcunov <gorcunov@...nvz.org>
To:	Oleg Nesterov <oleg@...hat.com>
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 Mon, Mar 26, 2012 at 06:43:47PM +0200, Oleg Nesterov wrote:
> 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?

Yes, but I wanted to be on safe side, and if one day user_ns_map_uid
get changed this function won't be security hole. Or I miss something
in general?

	Cyrill
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