From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755010Ab0KEWdx (ORCPT ); Fri, 5 Nov 2010 18:33:53 -0400 Received: from karen.lavabit.com ([72.249.41.33]:39658 "EHLO karen.lavabit.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754947Ab0KEWdv (ORCPT ); Fri, 5 Nov 2010 18:33:51 -0400 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=lavabit; d=lavabit.com; b=GwAlYPDDF91gUhWkiRzczyq7lASqOcoLF67hts5UTgfZd2tQL4kPLJO0edIF7NGtPgmSvqCmE0+8kXqtgjRkBIaXGpI243tetf5XuB9GWUHzqis9qOkhpcXnLlOWr3M3oVp/OCmGXHUggalh3dZimKjA/O2FdeZ2dlhHPMratMA=; h=Content-Type:Reply-To:To:Subject:Date:MIME-Version:Content-Transfer-Encoding:From:Message-ID:User-Agent; Content-Type: text/plain; charset=utf-8; format=flowed; delsp=yes Reply-To: abirvalg@lavabit.com To: linux-kernel@vger.kernel.org Subject: procfs doesnt honor cap_dac_override Date: Fri, 05 Nov 2010 18:33:45 -0400 MIME-Version: 1.0 Content-Transfer-Encoding: 7bit From: abirvalg@lavabit.com Message-ID: User-Agent: Opera Mail/10.60 (Linux) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org We have a folder /proc/1/fd which contains symlinks. A superuser can do readlink() on those symlinks. I expected that a non-root process with cap_dac_override capability set to EP could also readlink() those symlinks in /proc/1/fd, but alas "Permission denied". Just to make sure that my process isn't the culprit, I ran it as a regular user with UID=1000, I set cap_dac_override=ep and navigated to /root folder (which is readable only by root) and did readlink() there. It worked. (/root folder is on ext4.) Bottom line: procfs doesnt allow readlink() on certain symlinks owned by root even with cap_dac_override set. Is this an expected behaviour or is this a bug? Cheers.