From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andi Kleen <ak@muc.de>
Subject: Re: negative seek offsets in VFS
Date: 26 May 2005 21:25:26 +0200
Message-ID: <20050526192526.GX86087@muc.de>
References: <20050525163905.GP86087@muc.de> <20050526151508.GZ29811@parcelfarce.linux.theplanet.co.uk> <Pine.LNX.4.58.0505260822560.2307@ppc970.osdl.org>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Cc: Al Viro <viro@parcelfarce.linux.theplanet.co.uk>,
	viro@www.linux.org.uk, linux-fsdevel@vger.kernel.org
Return-path: <linux-fsdevel-owner@vger.kernel.org>
Received: from colin.muc.de ([193.149.48.1]:31502 "EHLO mail.muc.de")
	by vger.kernel.org with ESMTP id S261709AbVEZTZ1 (ORCPT
	<rfc822;linux-fsdevel@vger.kernel.org>);
	Thu, 26 May 2005 15:25:27 -0400
Date: Thu, 26 May 2005 21:25:26 +0200
To: Linus Torvalds <torvalds@osdl.org>
Content-Disposition: inline
In-Reply-To: <Pine.LNX.4.58.0505260822560.2307@ppc970.osdl.org>
Sender: linux-fsdevel-owner@vger.kernel.org
List-Id: linux-fsdevel.vger.kernel.org

> I don't think there is a "positive loff_t", so I guess the code would have 
> to be something like
> 
> 	/* Wraparound? */
> 	if ((u64)(pos + count) < count)
> 		goto Einval;

Sometimes I think we should have a nice inline asm macro for that
that checks carry. 

> 
> 	if ((loff_t) (pos + count) < 0)
> 		if (!(file->f_mode & FMODE_ANY_OFFSET))
> 			goto Einval;

Looks good. But how to handle the broken devices viro worries about? 
I would prefer not to open any new security holes, but it is a bit too
much code to audit all.  Flag would be possible, but ugly.

Any other choice?

-Andi