[PATCH v4 4/7] fs: Limit file caps to the user namespace of the super block

[Eric W. Biederman]

Seth Forshee <seth.forshee at canonical.com> writes:

> On Thu, Sep 24, 2015 at 04:59:35PM -0500, Eric W. Biederman wrote:
>> Seth Forshee <seth.forshee at canonical.com> writes:
>> 
>> > Capability sets attached to files must be ignored except in the
>> > user namespaces where the mounter is privileged, i.e. s_user_ns
>> > and its descendants. Otherwise a vector exists for gaining
>> > privileges in namespaces where a user is not already privileged.
>> >
>> > Add a new helper function, in_user_ns(), to test whether a user
>> > namespace is the same as or a descendant of another namespace.
>> > Use this helper to determine whether a file's capability set
>> > should be applied to the caps constructed during exec.
>> 
>> No issues with this but given that we always pass current_user_ns()
>> we may want to simplify the users of in_user_ns by renaming it
>> current_in_user_ns() and hard codeing current_user_ns().
>
> Sure, if that's what you prefer then I'll change it.

I took your patch as is.  This is a suggestion for a possible
incremental improvement.

Eric