Re: [REVIEW][PATCH 1/2] userns: Better restrictions on when proc andsysfs can be mounted

[Andy Lutomirski]

On Sat, Aug 31, 2013 at 9:45 PM, Eric W. Biederman
<ebiederm@xxxxxxxxxxxx> wrote:
> ebiederm@xxxxxxxxxxxx (Eric W. Biederman) writes:
>
>> Andy Lutomirski <luto@xxxxxxxxxxxxxx> writes:
>>
>>> On Tue, Aug 27, 2013 at 2:44 PM, Eric W. Biederman
>>> <ebiederm@xxxxxxxxxxxx> wrote:
>>>>
>>>> Rely on the fact that another flavor of the filesystem is already
>>>> mounted and do not rely on state in the user namespace.
>>>
>>> Possibly dumb question: does this check whether the pre-existing mount
>>> has hidepid set?
>>
>> Not currently.
>>
>> It may be worth doing something with respect to hidepid.  I forget what
>> hidepid tries to do, and I need to dash.  But feel free to cook up a
>> follow on patch.
>
> So I have thought about this a bit more.
>
> hidepid hides the processes that ptrace_may_access will fail on.
>
> You can only reach the point where an unprivileged mount of a pid
> namespace is possible if you have created both a user namespace and a
> pid namespace.  Which means the creator of the pid namespace will be
> capable of ptracing all of the other processes in the pid namespace
> (ignoring setns).
>
> So I don't see a point of worry about hidepid or the hidepid gid on
> child pid namespaces.  The cases it is attempting to protecting against
> really don't exist.

Fair enough.  I didn't realize that you had to own the pid namespace.

--Andy
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