linux-kernel - Re: [REVIEW][PATCH 1/3] ptrace: Capture the ptracer's creds not PT_PTRACE

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Date:   Fri, 18 Nov 2016 12:56:15 -0600
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Kees Cook <keescook@...omium.org>
Cc:     Linux Containers <containers@...ts.linux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm\@kvack.org" <linux-mm@...ck.org>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        Michal Hocko <mhocko@...nel.org>, Jann Horn <jann@...jh.net>,
        Willy Tarreau <w@....eu>, Andy Lutomirski <luto@...capital.net>
Subject: Re: [REVIEW][PATCH 1/3] ptrace: Capture the ptracer's creds not PT_PTRACE_CAP

Kees Cook <keescook@...omium.org> writes:

> On Thu, Nov 17, 2016 at 9:05 AM, Eric W. Biederman
> <ebiederm@...ssion.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@...r.kernel.org
>> Fixes: 4214e42f96d4 ("v2.4.9.11 -> v2.4.9.12")
>> Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.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