From: ebiederm@xmission.com (Eric W. Biederman)
To: Kees Cook <keescook@chromium.org>
Cc: Linux Containers <containers@lists.linux-foundation.org>,
        Oleg Nesterov <oleg@redhat.com>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-mm\@kvack.org" <linux-mm@kvack.org>,
        Linux FS Devel <linux-fsdevel@vger.kernel.org>,
        Michal Hocko <mhocko@kernel.org>, Jann Horn <jann@thejh.net>,
        Willy Tarreau <w@1wt.eu>, Andy Lutomirski <luto@amacapital.net>
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>
        <CALCETrU4SZYUEPrv4JkpUpA+0sZ=EirZRftRDp+a5hce5E7HgA@mail.gmail.com>
        <87y41kjn6l.fsf@xmission.com> <20161019172917.GE1210@laptop.thejh.net>
        <CALCETrWSY1SRse5oqSwZ=goQ+ZALd2XcTP3SZ8ry49C8rNd98Q@mail.gmail.com>
        <87pomwi5p2.fsf@xmission.com>
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        <87twb6avk8.fsf_-_@xmission.com> <87oa1eavfx.fsf_-_@xmission.com>
        <CAGXu5jKbVkCGVSoxNQ=pTCBX1Boe3rPR1P56P-kR9AHWYHBs2w@mail.gmail.com>
Date: Fri, 18 Nov 2016 12:56:15 -0600
In-Reply-To: <CAGXu5jKbVkCGVSoxNQ=pTCBX1Boe3rPR1P56P-kR9AHWYHBs2w@mail.gmail.com>
        (Kees Cook's message of "Thu, 17 Nov 2016 15:14:22 -0800")
Message-ID: <87y40gpqgg.fsf@xmission.com>
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1 (gnu/linux)
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Subject: Re: [REVIEW][PATCH 1/3] ptrace: Capture the ptracer's creds not PT_PTRACE_CAP
Sender: linux-kernel-owner@vger.kernel.org
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Kees Cook <keescook@chromium.org> writes:

> On Thu, Nov 17, 2016 at 9:05 AM, Eric W. Biederman
> <ebiederm@xmission.com> wrote:
>>
>> When the flag PT_PTRACE_CAP was added the PTRACE_TRACEME path was
>> overlooked.  This can result in incorrect behavior when an application
>> like strace traces an exec of a setuid executable.
>>
>> Further PT_PTRACE_CAP does not have enough information for making good
>> security decisions as it does not report which user namespace the
>> capability is in.  This has already allowed one mistake through
>> insufficient granulariy.
>>
>> I found this issue when I was testing another corner case of exec and
>> discovered that I could not get strace to set PT_PTRACE_CAP even when
>> running strace as root with a full set of caps.
>>
>> This change fixes the above issue with strace allowing stracing as
>> root a setuid executable without disabling setuid.  More fundamentaly
>> this change allows what is allowable at all times, by using the correct
>> information in it's decision.
>>
>> Cc: stable@vger.kernel.org
>> Fixes: 4214e42f96d4 ("v2.4.9.11 -> v2.4.9.12")
>> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
>> ---
>> [...]
>> diff --git a/include/linux/sched.h b/include/linux/sched.h
>> index 348f51b0ec92..8fe58255d219 100644
>> --- a/include/linux/sched.h
>> +++ b/include/linux/sched.h
>> @@ -1656,6 +1656,7 @@ struct task_struct {
>>         struct list_head cpu_timers[3];
>>
>>  /* process credentials */
>> +       const struct cred __rcu *ptracer_cred; /* Tracer's dredentials at attach */
>
> Typo: credentials.

Thank you, fixed.

Eric