Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755360Ab3JKDTX (ORCPT ); Thu, 10 Oct 2013 23:19:23 -0400 Received: from mail-pd0-f169.google.com ([209.85.192.169]:53672 "EHLO mail-pd0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752233Ab3JKDTV (ORCPT ); Thu, 10 Oct 2013 23:19:21 -0400 Message-ID: <52576E32.1050700@gmail.com> Date: Fri, 11 Oct 2013 14:19:14 +1100 From: Ryan Mallon User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.0 MIME-Version: 1.0 To: "Eric W. Biederman" , Joe Perches CC: Andrew Morton , eldad@fogrefinery.com, Jiri Kosina , jgunthorpe@obsidianresearch.com, Dan Rosenberg , Kees Cook , Alexander Viro , George Spelvin , "kernel-hardening@lists.openwall.com" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH v3a] vsprintf: Check real user/group id for %pK References: <5255D023.2030907@gmail.com> <1381356014.2050.28.camel@joe-AO722> <5255D2FD.6050705@gmail.com> <1381356861.2050.33.camel@joe-AO722> <5255D7D4.8050204@gmail.com> <1381358030.2050.36.camel@joe-AO722> <5255DBD8.30005@gmail.com> <1381360187.2050.44.camel@joe-AO722> <87pprck0q7.fsf@xmission.com> In-Reply-To: <87pprck0q7.fsf@xmission.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2060 Lines: 50 On 11/10/13 13:20, Eric W. Biederman wrote: > Joe Perches writes: > >> Some setuid binaries will allow reading of files which have read >> permission by the real user id. This is problematic with files which >> use %pK because the file access permission is checked at open() time, >> but the kptr_restrict setting is checked at read() time. If a setuid >> binary opens a %pK file as an unprivileged user, and then elevates >> permissions before reading the file, then kernel pointer values may be >> leaked. >> >> This happens for example with the setuid pppd application on Ubuntu >> 12.04: >> >> $ head -1 /proc/kallsyms >> 00000000 T startup_32 >> >> $ pppd file /proc/kallsyms >> pppd: In file /proc/kallsyms: unrecognized option 'c1000000' >> >> This will only leak the pointer value from the first line, but other >> setuid binaries may leak more information. >> >> Fix this by adding a check that in addition to the current process >> having CAP_SYSLOG, that effective user and group ids are equal to the >> real ids. If a setuid binary reads the contents of a file which uses >> %pK then the pointer values will be printed as NULL if the real user >> is unprivileged. >> >> Update the sysctl documentation to reflect the changes, and also >> correct the documentation to state the kptr_restrict=0 is the default. > > Sigh. This is all wrong. The only correct thing to test is > file->f_cred. Aka the capabilities of the program that opened the > file. > > Which means that the interface to %pK in the case of kptr_restrict is > broken as it has no way to be passed the information it needs to make > a sensible decision. Would it make sense to add a struct file * to struct seq_file and set that in seq_open? Then the capability check can be done against seq->file. ~Ryan -- 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/