From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-it0-f72.google.com (mail-it0-f72.google.com [209.85.214.72]) by kanga.kvack.org (Postfix) with ESMTP id 5B3776B037C for ; Thu, 17 Nov 2016 18:57:56 -0500 (EST) Received: by mail-it0-f72.google.com with SMTP id b123so5017688itb.3 for ; Thu, 17 Nov 2016 15:57:56 -0800 (PST) Received: from out02.mta.xmission.com (out02.mta.xmission.com. [166.70.13.232]) by mx.google.com with ESMTPS id k40si3935092iod.92.2016.11.17.15.57.55 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 17 Nov 2016 15:57:55 -0800 (PST) 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> <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> Date: Thu, 17 Nov 2016 17:55:16 -0600 In-Reply-To: (Andy Lutomirski's message of "Thu, 17 Nov 2016 15:29:43 -0800") Message-ID: <87mvgxwtjv.fsf@xmission.com> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [REVIEW][PATCH 2/3] exec: Don't allow ptracing an exec of an unreadable file Sender: owner-linux-mm@kvack.org List-ID: To: Andy Lutomirski 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 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. 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. 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