linux-kernel - Re: [RFC] c/r: prctl: Add ability to set new mm_struct::exe

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Message-ID: <20120305142655.GC9393@redhat.com>
Date:	Mon, 5 Mar 2012 15:26:55 +0100
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>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Kees Cook <keescook@...omium.org>, Tejun Heo <tj@...nel.org>
Subject: Re: [RFC] c/r: prctl: Add ability to set new mm_struct::exe_file

On 03/05, Oleg Nesterov wrote:
>
> On 03/04, Cyrill Gorcunov wrote:
> >
> > +	err = -EACCES;
> > +	if (!S_ISREG(dentry->d_inode->i_mode)	||
> > +	    exe_file->f_path.mnt->mnt_flags & MNT_NOEXEC)
> > +		goto exit;
> > +
> > +	if ((exe_file->f_flags & O_ACCMODE) != O_RDONLY)
> > +		goto exit;
> > +
> > +	err = inode_permission(dentry->d_inode, MAY_EXEC);
> > +	if (err)
> > +		goto exit;
>
> OK, I won't argue, probably this makes sense to make sure that
> admin can't get a heart attack looking at /proc/pid/exe.
>
> But the O_RDONLY check looks strange. We are not going to write
> to this file, we only set the name (and that is why I think it
> should be mm->exe_path). What is the point to check that the file
> was opened without FMODE_WRITE? Even if there were any security
> risk the apllication can open this file again with the different
> flags.

Seriously, I think we should cleanup this before c/r adds more
ugliness. I'll try to make the patch today.

And with all these checks I am no longer sure that fd is better
than filename ;)

Oleg.

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