Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754250Ab3JBTng (ORCPT ); Wed, 2 Oct 2013 15:43:36 -0400 Received: from mail-ie0-f180.google.com ([209.85.223.180]:58916 "EHLO mail-ie0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753610Ab3JBTne (ORCPT ); Wed, 2 Oct 2013 15:43:34 -0400 MIME-Version: 1.0 In-Reply-To: <20131002184844.GB3393@dztty> References: <1380659178-28605-1-git-send-email-tixxdz@opendz.org> <524B7999.60806@amacapital.net> <20131002143759.GA2966@dztty> <20131002182206.GB2485@dztty> <20131002184844.GB3393@dztty> Date: Wed, 2 Oct 2013 12:43:32 -0700 X-Google-Sender-Auth: iZXF0IaaBYxVJ7RqNa5g3tfbmvU Message-ID: Subject: Re: [PATCH v2 0/9] procfs: protect /proc//* files with file->f_cred From: Kees Cook To: Djalal Harouni Cc: Andy Lutomirski , "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 Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4095 Lines: 87 On Wed, Oct 2, 2013 at 11:48 AM, Djalal Harouni wrote: > On Wed, Oct 02, 2013 at 11:35:45AM -0700, Kees Cook wrote: >> On Wed, Oct 2, 2013 at 11:22 AM, Djalal Harouni wrote: >> > On Wed, Oct 02, 2013 at 10:48:55AM -0700, 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.) >> > Kees for 0400 on /proc/*/maps, it was reported that it could break glibc >> >> I didn't mean maps should be 0400. The maps file is already handled >> differently (pinning mm at open time). I didn't think it was one of >> the problematic files. > Kees currently all these files can be used to leak data, except for > /proc/*/{mem,environ} > > These are the only one that pin the mm at open time. But I'm not sure > that this solution will work for /proc/*/maps since they need vma info > which will be perhaps freed if task execv, Need to check it. Ah, yes, you're totally right. I had misremembered. -Kees -- Kees Cook Chrome OS Security -- 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/