From: Andy Lutomirski <luto@amacapital.net>
To: Jann Horn <jann@thejh.net>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>,
Michal Hocko <mhocko@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Linux Containers <containers@lists.linux-foundation.org>,
Oleg Nesterov <oleg@redhat.com>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
Linux FS Devel <linux-fsdevel@vger.kernel.org>
Subject: Re: [REVIEW][PATCH] exec: Don't exec files the userns root can not read.
Date: Wed, 19 Oct 2016 10:32:39 -0700 [thread overview]
Message-ID: <CALCETrWSY1SRse5oqSwZ=goQ+ZALd2XcTP3SZ8ry49C8rNd98Q@mail.gmail.com> (raw)
In-Reply-To: <20161019172917.GE1210@laptop.thejh.net>
On Wed, Oct 19, 2016 at 10:29 AM, Jann Horn <jann@thejh.net> wrote:
> On Wed, Oct 19, 2016 at 11:52:50AM -0500, Eric W. Biederman wrote:
>> Andy Lutomirski <luto@amacapital.net> writes:
>> > 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.
>
> Nope. check_unsafe_exec() sets LSM_UNSAFE_* flags in bprm->unsafe, and then
> the flags are checked by the LSMs and cap_bprm_set_creds() in commoncap.c.
> cap_bprm_set_creds() just degrades the execution to a non-setuid-ish one,
> and e.g. ptracers stay attached.
I think you're right. I ought to be completely sure because I rewrote
that code back in 2005 or so back when I thought kernel programming
was only for the cool kids. It was probably my first kernel patch
ever and it closed an awkward-to-exploit root hole. But it's been a
while. (Too bad my second (IIRC) kernel patch was more mundane and
fixed the mute button on "new" Lenovo X60-era laptops and spend
several years in limbo...)
--Andy
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next prev parent reply other threads:[~2016-10-19 17:32 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-17 16:39 [REVIEW][PATCH] mm: Add a user_ns owner to mm_struct and fix ptrace_may_access Eric W. Biederman
2016-10-17 17:25 ` Jann Horn
2016-10-17 17:33 ` Eric W. Biederman
2016-10-18 13:50 ` Michal Hocko
2016-10-18 13:57 ` Jann Horn
2016-10-18 14:56 ` Eric W. Biederman
2016-10-18 15:05 ` Jann Horn
2016-10-18 15:35 ` Eric W. Biederman
2016-10-18 19:12 ` Jann Horn
2016-10-18 21:07 ` Eric W. Biederman
2016-10-18 21:15 ` [REVIEW][PATCH] exec: Don't exec files the userns root can not read Eric W. Biederman
2016-10-19 6:13 ` Amir Goldstein
2016-10-19 13:33 ` Eric W. Biederman
2016-10-19 17:04 ` Eric W. Biederman
2016-10-19 15:30 ` Andy Lutomirski
2016-10-19 16:52 ` Eric W. Biederman
2016-10-19 17:29 ` Jann Horn
2016-10-19 17:32 ` Andy Lutomirski [this message]
2016-10-19 17:55 ` Eric W. Biederman
2016-10-19 18:38 ` Andy Lutomirski
2016-10-19 21:26 ` Eric W. Biederman
2016-10-19 23:17 ` Andy Lutomirski
2016-11-17 17:02 ` [REVIEW][PATCH 0/3] Fixing ptrace vs exec vs userns interactions Eric W. Biederman
2016-11-17 17:05 ` [REVIEW][PATCH 1/3] ptrace: Capture the ptracer's creds not PT_PTRACE_CAP Eric W. Biederman
2016-11-17 23:14 ` Kees Cook
2016-11-18 18:56 ` Eric W. Biederman
2016-11-17 23:27 ` Andy Lutomirski
2016-11-17 23:44 ` Eric W. Biederman
2016-11-17 17:08 ` [REVIEW][PATCH 2/3] exec: Don't allow ptracing an exec of an unreadable file Eric W. Biederman
2016-11-17 20:47 ` Willy Tarreau
2016-11-17 21:07 ` Kees Cook
2016-11-17 21:32 ` Willy Tarreau
2016-11-17 21:51 ` Eric W. Biederman
2016-11-17 22:50 ` [REVIEW][PATCH 2/3] ptrace: Don't allow accessing an undumpable mm Eric W. Biederman
2016-11-17 23:17 ` Kees Cook
2016-11-17 23:28 ` [REVIEW][PATCH 2/3] exec: Don't allow ptracing an exec of an unreadable file Andy Lutomirski
2016-11-17 23:29 ` Andy Lutomirski
2016-11-17 23:55 ` Eric W. Biederman
2016-11-18 0:10 ` Andy Lutomirski
2016-11-18 0:35 ` Eric W. Biederman
2016-11-17 17:10 ` [REVIEW][PATCH 3/3] exec: Ensure mm->user_ns contains the execed files Eric W. Biederman
2016-11-19 7:17 ` [REVIEW][PATCH 0/3] Fixing ptrace vs exec vs userns interactions Willy Tarreau
2016-11-19 9:28 ` Willy Tarreau
2016-11-19 9:33 ` Willy Tarreau
2016-11-19 18:44 ` Eric W. Biederman
2016-11-19 18:35 ` Eric W. Biederman
2016-11-19 18:37 ` Eric W. Biederman
2016-10-19 18:36 ` [REVIEW][PATCH] exec: Don't exec files the userns root can not read Andy Lutomirski
2016-10-18 18:06 ` [REVIEW][PATCH] mm: Add a user_ns owner to mm_struct and fix ptrace_may_access Michal Hocko
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