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From: Andy Lutomirski <luto@amacapital.net>
To: Kees Cook <keescook@chromium.org>
Cc: Will Drewry <wad@chromium.org>,
	linux-kernel@vger.kernel.org,
	Casey Schaufler <casey@schaufler-ca.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Jamie Lokier <jamie@shareable.org>,
	john.johansen@canonical.com, serge.hallyn@canonical.com,
	coreyb@linux.vnet.ibm.com, pmoore@redhat.com, eparis@redhat.com,
	djm@mindrot.org, segoon@openwall.com, rostedt@goodmis.org,
	jmorris@namei.org, scarybeasts@gmail.com, avi@redhat.com,
	penberg@cs.helsinki.fi, viro@zeniv.linux.org.uk, mingo@elte.hu,
	akpm@linux-foundation.org, khilman@ti.com,
	borislav.petkov@amd.com, amwang@redhat.com, oleg@redhat.com,
	ak@linux.intel.com, eric.dumazet@gmail.com, gregkh@suse.de,
	dhowells@redhat.com, daniel.lezcano@free.fr,
	linux-fsdevel@vger.kernel.org,
	linux-security-module@vger.kernel.org, olofj@chromium.org,
	mhalcrow@google.com, dlaor@redhat.com, corbet@lwn.net,
	alan@lxorguk.ukuu.org.uk
Subject: Re: [PATCH v3 3/4] Allow unprivileged CLONE_NEWUTS and CLONE_NEWIPC with no_new_privs
Date: Wed, 1 Feb 2012 12:35:33 -0800	[thread overview]
Message-ID: <CALCETrV6eMYGsw-AS+ZwLpTfdzbinJT_3or0hN+R=7PKmai4mg@mail.gmail.com> (raw)
In-Reply-To: <CAGXu5jK-4DaUVofwy3aqKnQTbyQGsLVmNNfAc1pjkJHt2Kfwww@mail.gmail.com>

On Wed, Feb 1, 2012 at 11:02 AM, Kees Cook <keescook@chromium.org> wrote:
> On Mon, Jan 30, 2012 at 8:17 AM, Andy Lutomirski <luto@amacapital.net> wrote:
>> They are normally disallowed because they could be used to subvert
>> setuid programs.  But if setuid is disabled, then they are safe.
>>
>> Signed-off-by: Andy Lutomirski <luto@amacapital.net>
>> ---
>>  kernel/nsproxy.c |    8 +++++++-
>>  1 files changed, 7 insertions(+), 1 deletions(-)
>>
>> diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
>> index b576f7f..47cf873 100644
>> --- a/kernel/nsproxy.c
>> +++ b/kernel/nsproxy.c
>> @@ -191,7 +191,13 @@ int unshare_nsproxy_namespaces(unsigned long unshare_flags,
>>                               CLONE_NEWNET)))
>>                return 0;
>>
>> -       if (!capable(CAP_SYS_ADMIN))
>> +       /* We require either no_new_privs or CAP_SYS_ADMIN for all modes */
>> +       if (!current->no_new_privs && !capable(CAP_SYS_ADMIN))
>> +               return -EPERM;
>> +
>> +       /* NEWNS and NEWNET always require CAP_SYS_ADMIN. */
>> +       if ((unshare_flags & (CLONE_NEWNS | CLONE_NEWNET)) &&
>> +           !capable(CAP_SYS_ADMIN))
>>                return -EPERM;
>>
>>        *new_nsp = create_new_namespaces(unshare_flags, current,
>
> While I think it's unlikely that the list handled by
> unshare_nsproxy_namespaces() is going to change, I'd still prefer that
> the logic of this test be reversed so that the nnp-allowed flags are
> listed instead of the CAP_SYS_ADMIN-required ones so that it will
> default to disallowing new flags. It's a little less readable, but
> maybe something like this (untested):
>
> unsigned long handled_mask = (CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC |
>                                 CLONE_NEWNET);
> unsigned long npp_mask = (CLONE_NEWUTS | CLONE_NEWIPC);
>
> if (!(unshare_flags & handled_mask))
>        return 0;
>
> if (  !(current->no_new_privs &&
>        !(unshare_flags & (handled_mask ^ npp_mask))) &&
>      !capable(CAP_SYS_ADMIN))
>        return -EPERM;
> ...
>
> This also has the side-effect of removing the double-check of
> capable() in some cases.

Agreed -- will fix.

This patch is also missing the corresponding change for clone.  I'll add that.

I'm tempted to add CLONE_NEWPID as well (it's _useful_), but there's
an unresolved issue with SCM_CREDENTIALS.

--Andy

  reply	other threads:[~2012-02-01 20:36 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-01-30 16:17 [PATCH v3 0/4] PR_SET_NO_NEW_PRIVS, unshare, and chroot Andy Lutomirski
2012-01-30 16:17 ` [PATCH v3 1/4] Add PR_{GET,SET}_NO_NEW_PRIVS to prevent execve from granting privs Andy Lutomirski
2012-02-01 18:14   ` Kees Cook
2012-01-30 16:17 ` [PATCH v3 2/4] Fix apparmor for PR_{GET,SET}_NO_NEW_PRIVS Andy Lutomirski
2012-01-30 16:17 ` [PATCH v3 3/4] Allow unprivileged CLONE_NEWUTS and CLONE_NEWIPC with no_new_privs Andy Lutomirski
2012-02-01 19:02   ` Kees Cook
2012-02-01 20:35     ` Andy Lutomirski [this message]
2012-01-30 16:17 ` [PATCH v3 4/4] Allow unprivileged chroot when safe Andy Lutomirski
2012-01-30 21:58   ` Colin Walters
2012-01-30 22:10     ` Andy Lutomirski
2012-01-30 22:41       ` Colin Walters
2012-01-30 22:43         ` Andy Lutomirski
2012-01-30 23:10           ` Colin Walters
2012-01-30 23:15             ` Andy Lutomirski
2012-01-30 23:55               ` Colin Walters
2012-01-31  0:13                 ` Andy Lutomirski
2012-01-30 22:18     ` Steven Rostedt
2012-01-30 22:28       ` Andy Lutomirski
2012-01-30 22:38       ` Will Drewry
2012-01-30 22:48         ` Colin Walters
2012-01-30 22:51         ` Andy Lutomirski
2012-02-09  9:35           ` Vasiliy Kulikov

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