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From: Kees Cook <keescook@chromium.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Jann Horn <jann@thejh.net>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Roland McGrath <roland@hack.frob.com>,
	John Johansen <john.johansen@canonical.com>,
	James Morris <james.l.morris@oracle.com>,
	"Serge E. Hallyn" <serge@hallyn.com>,
	Paul Moore <aul@paul-moore.com>,
	Stephen Smalley <sds@tycho.nsa.gov>,
	Eric Paris <eparis@parisplace.org>,
	Casey Schaufler <casey@schaufler-ca.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Janis Danisevskis <jdanis@google.com>,
	Seth Forshee <seth.forshee@canonical.com>,
	"Eric . Biederman" <ebiederm@xmission.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Benjamin LaHaise <bcrl@kvack.org>,
	Ben Hutchings <ben@decadent.org.uk>,
	Andy Lutomirski <luto@amacapital.net>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	linux-security-module <linux-security-module@vger.kernel.org>,
	"security@kernel.org" <security@kernel.org>
Subject: Re: [PATCH v2 2/8] exec: turn self_exec_id into self_privunit
Date: Fri, 30 Sep 2016 11:30:23 -0700	[thread overview]
Message-ID: <CAGXu5j+Oe+Be+ca+V3OKZCUiFzqQtj6CoH=FeEWvY98YfcoJxQ@mail.gmail.com> (raw)
In-Reply-To: <20160930134404.GA12862@redhat.com>

On Fri, Sep 30, 2016 at 6:44 AM, Oleg Nesterov <oleg@redhat.com> wrote:
> forgot to mention...
>
> On 09/30, Oleg Nesterov wrote:
>>
>> On 09/23, Jann Horn wrote:
>> >
>> > One reason for doing this is that it prevents an attacker from sending an
>> > arbitrary signal to a parent process after performing 2^32-1 execve()
>> > calls.
>
> No, sets ->exit_signal = SIGCHLD. So the only problem is that the parent
> can do clone(SIGKILL), then do execve() 2^32-1 times, then it can be killed
> by SIGKILL from the exiting child.
>
> Honestly, I do not think this is security problem.

It's a corner case, to be sure. But even sending a SIGKILL across
privilege boundaries should not be allowed to happen.

>
>> I think we should simply kill self/parent_exec_id's. I am going to send
>> the patch below after re-check/testing.
>
> Yes, I think this makes sense anyway.

Hrm, I also thought this was used for more than just signal checking,
but I don't see anything else right now. Maybe I was remembering
earlier versions of Jann's patches...

-Kees

-- 
Kees Cook
Nexus Security

  reply	other threads:[~2016-09-30 18:30 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-09-23 20:40 [PATCH v2 0/8] Various fixes related to ptrace_may_access() Jann Horn
2016-09-23 20:40 ` [PATCH v2 1/8] exec: introduce cred_guard_light Jann Horn
2016-09-30 15:35   ` Oleg Nesterov
2016-09-30 18:27     ` Eric W. Biederman
2016-10-03 16:02       ` Oleg Nesterov
2016-10-30 21:12     ` Jann Horn
2016-09-23 20:40 ` [PATCH v2 2/8] exec: turn self_exec_id into self_privunit Jann Horn
2016-09-23 21:04   ` Andy Lutomirski
2016-09-23 21:33     ` Jann Horn
2016-09-30 13:20   ` Oleg Nesterov
2016-09-30 13:44     ` Oleg Nesterov
2016-09-30 18:30       ` Kees Cook [this message]
2016-09-30 18:59         ` Jann Horn
2016-09-30 19:05           ` Kees Cook
2016-10-03 16:37         ` Oleg Nesterov
2016-09-23 20:40 ` [PATCH v2 3/8] proc: use open()-time creds for ptrace checks Jann Horn
2016-09-23 20:40 ` [PATCH v2 4/8] futex: don't leak robust_list pointer Jann Horn
2016-09-30 14:52   ` Oleg Nesterov
2016-10-30 17:16     ` Jann Horn
2016-11-02 21:39       ` Jann Horn
2016-11-02 22:47         ` Jann Horn
2016-09-23 20:40 ` [PATCH v2 5/8] proc: lock properly in ptrace_may_access callers Jann Horn
2016-09-23 20:40 ` [PATCH v2 6/8] ptrace: warn on ptrace_may_access without proper locking Jann Horn
2016-09-23 20:40 ` [PATCH v2 7/8] fs/proc: fix attr access check Jann Horn
2016-09-23 20:40 ` [PATCH v2 8/8] Documentation: add security/ptrace_checks.txt Jann Horn
2016-10-02  3:16   ` Krister Johansen
2016-10-30 19:09     ` Jann Horn
2016-10-31  4:14       ` Eric W. Biederman
2016-10-31 13:39         ` Jann Horn
2016-11-03 20:43         ` Krister Johansen

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