[PATCH] KEYS: allow changing key ownership with CAP_SYS_ADMIN in a NS

Eric W. Biederman ebiederm at xmission.com
Tue Oct 3 14:51:14 UTC 2017


"Serge E. Hallyn" <serge at hallyn.com> writes:

> On Mon, Oct 02, 2017 at 10:30:43PM -0500, Eric W. Biederman wrote:
>> Dimitri John Ledkov <xnox at ubuntu.com> writes:
>> 
>> > Currently, changing key ownership from one namespaced uid/gid to
>> > another namespaced uid/gid is only allowed by processes that have
>> > CAP_SYS_ADMIN in the intial namespace. Fix the capability check to
>> > also check the capability in the current capability.
>> 
>> Nacked-by: "Eric W. Biederman" <ebiederm at xmission.com>
>> 
>> I won't deny the issue, but unless I am misreading something this
>> will allow me to change the the uid of any key simply by unsharing
>> a user namespace.  At which point there is no point in having a
>> permission check at all.
>
> Right so without having looked closely, at the very least you need to
> verify that the ucrrent user is privileged over key->{uid,gid} and
> over @user and @group.  Now the latter is I *think* being done
> implicitly by the make_kuid(current_user_ns, user) at the top.  So
> you need to further verify that key->uid and key->gid are mapped into
> current_user_ns.
>
> That *may* be sufficient.

Yes.  It sounds like either we need to change something in the
implementation of keys so they have a clear user namespace owner
or implement capable_wrt_key_uidgid.

The latter is tricky so at the very least I would prefer it have a
function of it's own.  Just so people don't handroll the necessary
pattern incorrectly at different places.

Eric


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