From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ua0-f199.google.com (mail-ua0-f199.google.com [209.85.217.199]) by kanga.kvack.org (Postfix) with ESMTP id D6FBB6B0382 for ; Thu, 17 Nov 2016 19:11:08 -0500 (EST) Received: by mail-ua0-f199.google.com with SMTP id b35so153896633uaa.1 for ; Thu, 17 Nov 2016 16:11:08 -0800 (PST) Received: from mail-vk0-x22c.google.com (mail-vk0-x22c.google.com. [2607:f8b0:400c:c05::22c]) by mx.google.com with ESMTPS id l22si1653680uaa.184.2016.11.17.16.11.08 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 17 Nov 2016 16:11:08 -0800 (PST) Received: by mail-vk0-x22c.google.com with SMTP id x186so155996429vkd.1 for ; Thu, 17 Nov 2016 16:11:08 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <87mvgxwtjv.fsf@xmission.com> 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> <87y41kjn6l.fsf@xmission.com> <20161019172917.GE1210@laptop.thejh.net> <87pomwi5p2.fsf@xmission.com> <87pomwghda.fsf@xmission.com> <87twb6avk8.fsf_-_@xmission.com> <87inrmavax.fsf_-_@xmission.com> <87mvgxwtjv.fsf@xmission.com> From: Andy Lutomirski Date: Thu, 17 Nov 2016 16:10:47 -0800 Message-ID: Subject: Re: [REVIEW][PATCH 2/3] exec: Don't allow ptracing an exec of an unreadable file Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: "Eric W. Biederman" Cc: Linux Containers , Oleg Nesterov , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , Linux FS Devel , Michal Hocko , Jann Horn , Willy Tarreau , Kees Cook On Thu, Nov 17, 2016 at 3:55 PM, Eric W. Biederman wrote: > Andy Lutomirski writes: > >> On Thu, Nov 17, 2016 at 9:08 AM, Eric W. Biederman >> wrote: >>> >>> It is the reasonable expectation that if an executable file is not >>> readable there will be no way for a user without special privileges to >>> read the file. This is enforced in ptrace_attach but if we are >>> already attached there is no enforcement if a readonly executable >>> is exec'd. >>> >>> Therefore do the simple thing and if there is a non-dumpable >>> executable that we are tracing without privilege fail to exec it. >>> >>> Fixes: v1.0 >>> Cc: stable@vger.kernel.org >>> Reported-by: Andy Lutomirski >>> Signed-off-by: "Eric W. Biederman" >>> --- >>> fs/exec.c | 8 +++++++- >>> 1 file changed, 7 insertions(+), 1 deletion(-) >>> >>> diff --git a/fs/exec.c b/fs/exec.c >>> index fdec760bfac3..de107f74e055 100644 >>> --- a/fs/exec.c >>> +++ b/fs/exec.c >>> @@ -1230,6 +1230,11 @@ int flush_old_exec(struct linux_binprm * bprm) >>> { >>> int retval; >>> >>> + /* Fail if the tracer can't read the executable */ >>> + if ((bprm->interp_flags & BINPRM_FLAGS_ENFORCE_NONDUMP) && >>> + !ptracer_capable(current, bprm->mm->user_ns)) >>> + return -EPERM; >>> + >> >> At the very least, I think that BINPRM_FLAGS_ENFORCE_NONDUMP needs to >> check capable_wrt_inode_uidgid too. Otherwise we risk breaking: >> >> $ gcc whatever.c >> $ chmod 400 a.out >> $ strace a.out > > It is an invariant that if you have caps in mm->user_ns you will > also be capable_write_inode_uidgid of all files that a process exec's. I meant to check whether you *are* the owner, too. > > My third patch winds up changing mm->user_ns to maintain this invariant. > > It is also true that Willy convinced me while this check is trivial it > will break historic uses so I have replaced this patch with: > "ptrace: Don't allow accessing an undumpable mm. I think that's better. > > Eric > > -- Andy Lutomirski AMA Capital Management, LLC -- 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