Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755100Ab3JBS0u (ORCPT ); Wed, 2 Oct 2013 14:26:50 -0400 Received: from numidia.opendz.org ([98.142.220.152]:46756 "EHLO numidia.opendz.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753694Ab3JBS0t (ORCPT ); Wed, 2 Oct 2013 14:26:49 -0400 Date: Wed, 2 Oct 2013 19:26:43 +0100 From: Djalal Harouni To: Andy Lutomirski Cc: Kees Cook , "Eric W. Biederman" , Al Viro , Andrew Morton , Linus Torvalds , Ingo Molnar , "Serge E. Hallyn" , Cyrill Gorcunov , David Rientjes , LKML , Linux FS Devel , "kernel-hardening@lists.openwall.com" , Djalal Harouni Subject: Re: [PATCH v2 0/9] procfs: protect /proc//* files with file->f_cred Message-ID: <20131002182643.GC2485@dztty> References: <1380659178-28605-1-git-send-email-tixxdz@opendz.org> <524B7999.60806@amacapital.net> <20131002143759.GA2966@dztty>

MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4345 Lines: 100 On Wed, Oct 02, 2013 at 11:00:26AM -0700, Andy Lutomirski wrote: > On Wed, Oct 2, 2013 at 10:48 AM, Kees Cook wrote: > > On Wed, Oct 2, 2013 at 9:51 AM, Andy Lutomirski wrote: > >> On Wed, Oct 2, 2013 at 3:37 PM, Djalal Harouni wrote: > >>> On Tue, Oct 01, 2013 at 06:40:41PM -0700, Andy Lutomirski wrote: > >>>> On 10/01/2013 01:26 PM, Djalal Harouni wrote: > >>>> > /proc//* entries varies at runtime, appropriate permission checks > >>>> > need to happen during each system call. > >>>> > > >>>> > Currently some of these sensitive entries are protected by performing > >>>> > the ptrace_may_access() check. However even with that the /proc file > >>>> > descriptors can be passed to a more privileged process > >>>> > (e.g. a suid-exec) which will pass the classic ptrace_may_access() > >>>> > check. In general the ->open() call will be issued by an unprivileged > >>>> > process while the ->read(),->write() calls by a more privileged one. > >>>> > > >>>> > Example of these files are: > >>>> > /proc/*/syscall, /proc/*/stack etc. > >>>> > > >>>> > And any open(/proc/self/*) then suid-exec to read()/write() /proc/self/* > >>>> > > >>>> > > >>>> > These files are protected during read() by the ptrace_may_access(), > >>>> > however the file descriptor can be passed to a suid-exec which can be > >>>> > used to read data and bypass ASLR. Of course this was discussed several > >>>> > times on LKML. > >>>> > >>>> Can you elaborate on what it is that you're fixing? That is, can you > >>>> give a concrete example of what process opens what file and passes the > >>>> fd to what process? > >>> Yes, the references were already given in this email: > >>> https://lkml.org/lkml/2013/8/31/209 > >>> > >>> This has been discussed several times on lkml: > >>> https://lkml.org/lkml/2013/8/28/544 > >>> > >>> https://lkml.org/lkml/2013/8/28/564 (check Kees's references) > >>> > >>> > >>>> I'm having trouble following your description. > >>> Process open a /proc file and pass the fd to a more privilaged process > >>> that will pass the ptrace_may_access() check, while the original process > >>> that opened that file should fail at the ptrace_may_access() > >> > >> So we're talking about two kinds of attacks, right? > > > > Correct. > > > >> Type 1: Unprivileged process does something like open("/proc/1/maps", > >> O_RDONLY) and then passes the resulting fd to something privileged. > > > > ... and then leaks contents back to unprivileged process. > > > >> Type 2: Unprivileged process does something like > >> open("/proc/self/maps", O_RDONLY) and then forks. The parent calls > >> execve on something privileged. > > > > ... and then parent snoops on file contents for the privileged child. > > > > (Type 2 is solved currently, IIUC. Type 1 could be reduced in scope by > > changing these file modes back to 0400.) > > > >> Can we really not get away with fixing type 1 by preventing these > >> files from being opened in the first place and type 2 by revoking all > >> of these fds when a privilege-changing exec happens? > > > > Type 1 can be done via exec as well. Instead of using a priv exec to > > read an arbitrary process, read it could read its own. > > Right. > > > > > I think revoking the fd would be great. Does that mechanism exist? > > There's this thing that never got merged. > > http://thread.gmane.org/gmane.linux.kernel/1523331 > > But doing it more directly should be reasonably straightforward. Either: > > (a) when a process execs and privileges change, find all the old proc > inodes, mark them dead, and unlink them, or Will take a look at it. > (b) add self_exec_id to all the proc file private_data entries (or > somewhere else). Then just make sure that they're unchanged. I think > the bug last time around was because the self_exec_id and struct pid > weren't being compared together. The bug was about self_exec_id not beeing unique. self_exec_id stuff must be unique during life time as it's done currently in grsecurity with exec_id. -- Djalal Harouni http://opendz.org -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/