From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f200.google.com (mail-pf0-f200.google.com [209.85.192.200]) by kanga.kvack.org (Postfix) with ESMTP id 8E9536B0267 for ; Wed, 19 Oct 2016 12:54:59 -0400 (EDT) Received: by mail-pf0-f200.google.com with SMTP id e6so1349129pfk.2 for ; Wed, 19 Oct 2016 09:54:59 -0700 (PDT) Received: from out02.mta.xmission.com (out02.mta.xmission.com. [166.70.13.232]) by mx.google.com with ESMTPS id a15si13235890pfa.272.2016.10.19.09.54.58 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 19 Oct 2016 09:54:58 -0700 (PDT) From: ebiederm@xmission.com (Eric W. Biederman) References: <87twcbq696.fsf@x220.int.ebiederm.org> <20161018135031.GB13117@dhcp22.suse.cz> <8737jt903u.fsf@xmission.com> <20161018150507.GP14666@pc.thejh.net> <87twc9656s.fsf@xmission.com> <20161018191206.GA1210@laptop.thejh.net> <87r37dnz74.fsf@xmission.com> <87k2d5nytz.fsf_-_@xmission.com> Date: Wed, 19 Oct 2016 11:52:50 -0500 In-Reply-To: (Andy Lutomirski's message of "Wed, 19 Oct 2016 08:30:14 -0700") Message-ID: <87y41kjn6l.fsf@xmission.com> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [REVIEW][PATCH] exec: Don't exec files the userns root can not read. Sender: owner-linux-mm@kvack.org List-ID: To: Andy Lutomirski Cc: Jann Horn , Michal Hocko , "linux-kernel@vger.kernel.org" , Linux Containers , Oleg Nesterov , "linux-mm@kvack.org" , Linux FS Devel Andy Lutomirski writes: > On Tue, Oct 18, 2016 at 2:15 PM, Eric W. Biederman > wrote: >> >> When the user namespace support was merged the need to prevent >> ptracing an executable that is not readable was overlooked. > > Before getting too excited about this fix, isn't there a much bigger > hole that's been there forever? In this case it was a newish hole (2011) that the user namespace support added that I am closing. I am not super excited but I figure it is useful to make the kernel semantics at least as secure as they were before. > Simply ptrace yourself, exec the > program, and then dump the program out. A program that really wants > to be unreadable should have a stub: the stub is setuid and readable, > but all the stub does is to exec the real program, and the real > program should have mode 0500 or similar. > > ISTM the "right" check would be to enforce that the program's new > creds can read the program, but that will break backwards > compatibility. Last I looked I had the impression that exec of a setuid program kills the ptrace. If we are talking about a exec of a simple unreadable executable (aka something that sets undumpable but is not setuid or setgid). Then I agree it should break the ptrace as well and since those programs are as rare as hens teeth I don't see any problem with changing the ptrace behavior in that case. Eric -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org