On pią, 2015-07-31 at 22:48 -0500, Serge E. Hallyn wrote:
> On Fri, Jul 31, 2015 at 11:28:56AM +0200, Lukasz Pawelczyk wrote:
> > On czw, 2015-07-30 at 16:30 -0500, Serge E. Hallyn wrote:
> > > On Fri, Jul 24, 2015 at 12:04:35PM +0200, Lukasz Pawelczyk wrote:
> > > > @@ -969,6 +982,7 @@ static int userns_install(struct nsproxy
> > > > *nsproxy, struct ns_common *ns)
> > > > {
> > > > struct user_namespace *user_ns = to_user_ns(ns);
> > > > struct cred *cred;
> > > > + int err;
> > > >
> > > > /* Don't allow gaining capabilities by reentering
> > > > * the same user namespace.
> > > > @@ -986,6 +1000,10 @@ static int userns_install(struct nsproxy
> > > > *nsproxy, struct ns_common *ns)
> > > > if (!ns_capable(user_ns, CAP_SYS_ADMIN))
> > > > return -EPERM;
> > > >
> > > > + err = security_userns_setns(nsproxy, user_ns);
> > > > + if (err)
> > > > + return err;
> > >
> > > So at this point the LSM thinks current is in the new ns. If
> > > prepare_creds() fails below, should it be informed of that?
> > > (Or am I over-thinking this?)
> > >
> > > > +
> > > > cred = prepare_creds();
> > > > if (!cred)
> > > > return -ENOMEM;
> >
> > Hmm, the use case for this hook I had in mind was just to allow or
> > disallow the operation based on the information passed in
> > arguments.
> > Not to register the current in any way so LSM can think it is or
> > isn't
> > in the new namespace.
> >
> > I think that any other LSM check that would like to know in what
> > namespace the current is, would just check that from current's
> > creds.
> > Not use some stale and duplicated information the above hook could
> > have
> > registered.
> >
> > I see no reason for this hook to change the LSM state, only to
> > answer
> > the question: allowed/disallowed (eventually return an error cause
> > it
> > is unable to give an answer which falls into the disallow
> > category).
>
> How about renaming it "security_userns_may_setns()" for clarity?
I personally have nothing against it. However looking at already
existing hooks only one of them has "may" in the name (unix_may_send)
while a lot clearly have exactly this purpose (e.g. most of inode_*
family, some from file_* and task_*). So it seems the trend is against
it.
What do you think? Anyone else has an opinion?
--
Lukasz Pawelczyk
Samsung R&D Institute Poland
Samsung Electronics
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