linux-kernel - Re: [PATCH 1/3] capabilities: user namespace capabilities

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Date: Tue, 21 May 2024 08:52:14 -0700
From: John Johansen <john.johansen@...onical.com>
To: "Eric W. Biederman" <ebiederm@...ssion.com>,
 Jonathan Calmels <jcalmels@...0.net>
Cc: brauner@...nel.org, Luis Chamberlain <mcgrof@...nel.org>,
 Kees Cook <keescook@...omium.org>, Joel Granados <j.granados@...sung.com>,
 Serge Hallyn <serge@...lyn.com>, Paul Moore <paul@...l-moore.com>,
 James Morris <jmorris@...ei.org>, David Howells <dhowells@...hat.com>,
 Jarkko Sakkinen <jarkko@...nel.org>, containers@...ts.linux.dev,
 linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
 linux-security-module@...r.kernel.org, keyrings@...r.kernel.org
Subject: Re: [PATCH 1/3] capabilities: user namespace capabilities

On 5/17/24 07:22, Eric W. Biederman wrote:
> Jonathan Calmels <jcalmels@...0.net> writes:
> 
>> On Fri, May 17, 2024 at 06:32:46AM GMT, Eric W. Biederman wrote:
>>>
>>> Pointers please?
>>>
>>> That sentence sounds about 5 years out of date.
>>
>> The link referenced is from last year.
>> Here are some others often cited by distributions:
>>
>> https://nvd.nist.gov/vuln/detail/CVE-2022-0185
>> https://nvd.nist.gov/vuln/detail/CVE-2022-1015
>> https://nvd.nist.gov/vuln/detail/CVE-2022-2078
>> https://nvd.nist.gov/vuln/detail/CVE-2022-24122
>> https://nvd.nist.gov/vuln/detail/CVE-2022-25636
>>
>> Recent thread discussing this too:
>> https://seclists.org/oss-sec/2024/q2/128
> 
> My apologies perhaps I trimmed too much.
> 
> I know that user namespaces enlarge the attack surface.
> How much and how serious could be debated but for unprivileged
> users the attack surface is undoubtedly enlarged.
> 
> As I read your introduction you were justifying the introduction
> of a new security mechanism with the observation that distributions
> were carrying distribution specific patches.
> 
> To the best of my knowledge distribution specific patches and
> distributions disabling user namespaces have been gone for quite a
> while.  So if that has changed recently I would like to know.
> 

almost all the distros are carrying the out of try sysctl to disable
user namepsaces. Its disabled by default but is available. Ubuntu in
its 24.04 release is now limiting unprivileged use of user namespaces
to known code. At a generic code level they are allowed but with no
capabilities within the user namespace.