Re: [PATCH] devpts: Add ptmx_uid and ptmx_gid options

From: Kenton Varda
Date: Thu May 28 2015 - 16:23:55 EST


On Thu, May 28, 2015 at 1:06 PM, Alexander Larsson <alexl@xxxxxxxxxx> wrote:
> On Thu, 2015-05-28 at 12:14 -0500, Eric W. Biederman wrote:
>>
>> > Where does the second namespace enter into this?
>>
>> Step a. Create create a user namespace where uid 0 is mapped to your
>> real uid, and set up your sandbox (aka mount /dev/pts and everything
>> else).
>>
>> Step b. Create a nested user namespace where your uid is identity
>> mapped and run your desktop application. You can even drop all caps
>> in
>> your namespace.
>
> Just tried this. Its not the nicest, and it doubles the number of
> namespaces in action for each sandbox, but it does work.

How much overhead is involved in each user namespace? Is there any
system-wide limit on total namespaces, other than RAM? Is there
(non-negligible) CPU overhead for each syscall seeking permissions in
the namespace?

-Kenton
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