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Subject: Re: [PATCH] userns/capability: Add user namespace capability
To: Tobias Markus <tobias@miglix.eu>
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From: Richard Weinberger <richard@nod.at>
Message-ID: <5623FF36.8080800@nod.at>
Date: Sun, 18 Oct 2015 22:21:10 +0200
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Am 18.10.2015 um 22:13 schrieb Tobias Markus:
> On 17.10.2015 22:17, Richard Weinberger wrote:
>> On Sat, Oct 17, 2015 at 5:58 PM, Tobias Markus <tobias@miglix.eu> wrote:
>>> One question remains though: Does this break userspace executables that
>>> expect being able to create user namespaces without priviledge? Since
>>> creating user namespaces without CAP_SYS_ADMIN was not possible before
>>> Linux 3.8, programs should already expect a potential EPERM upon calling
>>> clone. Since creating a user namespace without CAP_SYS_USER_NS would
>>> also cause EPERM, we should be on the safe side.
>>
>> In case of doubt, yes it will break existing software.
>> Hiding user namespaces behind CAP_SYS_USER_NS will not magically
>> make them secure.
>>
> The goal is not to make user namespaces secure, but to limit access to
> them somewhat in order to reduce the potential attack surface.

We have already a framework to reduce the attack surface, seccomp.
There is no need to invent new capabilities for every non-trivial
kernel feature.

I can understand the user namespaces seems scary and had bugs.
But which software didn't?

Are there any unfixed exploitable bugs in user namespaces in recent kerenls?

Thanks,
//richard