From: ebiederm@xmission.com (Eric W. Biederman)
To: Jann Horn <jannh@google.com>
Cc: Nagarathnam Muthusamy <nagarathnam.muthusamy@oracle.com>,
kernel list <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Serge Hallyn <serge.hallyn@ubuntu.com>,
Oleg Nesterov <oleg@redhat.com>,
Prakash Sangappa <prakash.sangappa@oracle.com>,
Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
Andy Lutomirski <luto@amacapital.net>
Subject: Re: [RFC] Allow user namespace inside chroot
Date: Mon, 15 Oct 2018 13:07:21 -0500 [thread overview]
Message-ID: <87o9bvm6cm.fsf@xmission.com> (raw)
In-Reply-To: <CAG48ez2cHT1U5nn+dNCAg3Lk5047=Tr20T8HkKhBUt1Mv+gNeg@mail.gmail.com> (Jann Horn's message of "Mon, 15 Oct 2018 19:22:12 +0200")
Jann Horn <jannh@google.com> writes:
> On Mon, Oct 15, 2018 at 7:10 PM <nagarathnam.muthusamy@oracle.com> wrote:
>> @@ -1281,7 +1285,7 @@ static int userns_install(struct nsproxy *nsproxy, struct ns_common *ns)
>> return -ENOMEM;
>>
>> put_user_ns(cred->user_ns);
>> - set_cred_user_ns(cred, get_user_ns(user_ns));
>> + set_cred_user_ns(cred, get_user_ns(user_ns), 0);
>
> This looks bogus. With this, I think your restriction can be bypassed
> if process A forks a child B, B creates a new user namespace, then A
> enters the user namespace with setns() and has full capabilities. Am I
> missing something?
Nope. I feel silly for missing that angle.
Even without the full capabilities the userns_install angle will place
you at the root of the mount namespace outside of the chroot.
At which point I have visions of the special cases multiplying like
bunnies make this work. Without a very strong case I don't like this at all.
Eric
next prev parent reply other threads:[~2018-10-15 18:07 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-15 17:10 [RFC] Allow user namespace inside chroot nagarathnam.muthusamy
2018-10-15 17:22 ` Jann Horn
2018-10-15 17:27 ` Andy Lutomirski
2018-10-15 18:07 ` Eric W. Biederman [this message]
2018-10-15 17:42 ` Eric W. Biederman
2018-10-15 18:00 ` Nagarathnam Muthusamy
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