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Message-ID: <1509627538.4623.1.camel@tycho.nsa.gov>
Date: Thu, 02 Nov 2017 08:58:58 -0400
From: Stephen Smalley <sds@...ho.nsa.gov>
To: Paul Moore <paul@...l-moore.com>, Florian Westphal <fw@...len.de>
Cc: herbert@...dor.apana.org.au, netdev@...r.kernel.org,
linux-security-module@...r.kernel.org, selinux@...ho.nsa.gov,
davem@...emloft.net
Subject: Re: [RFC PATCH] xfrm: fix regression introduced by xdst pcpu cache
On Wed, 2017-11-01 at 17:39 -0400, Paul Moore wrote:
> On Tue, Oct 31, 2017 at 7:08 PM, Florian Westphal <fw@...len.de>
> wrote:
> > Paul Moore <paul@...l-moore.com> wrote:
> > > On Mon, Oct 30, 2017 at 10:58 AM, Stephen Smalley <sds@...ho.nsa.
> > > gov> wrote:
> > > > matching before (as in this patch) or after calling
> > > > xfrm_bundle_ok()?
> > >
> > > I would probably make the LSM call the last check, as you've
> > > done; but
> > > I have to say that is just so it is consistent with the "LSM
> > > last"
> > > philosophy and not because of any performance related argument.
> > >
> > > > ... Also,
> > > > do we need to test xfrm->sel.family before calling
> > > > xfrm_selector_match
> > > > (as in this patch) or not - xfrm_state_look_at() does so when
> > > > the
> > > > state is XFRM_STATE_VALID but not when it is _ERROR or
> > > > _EXPIRED?
> > >
> > > Speaking purely from a SELinux perspective, I'm not sure it
> > > matters:
> > > as long as the labels match we are happy. However, from a
> > > general
> > > IPsec perspective it does seem like a reasonable thing.
> > >
> > > Granted I'm probably missing something, but it seems a little odd
> > > that
> > > the code isn't already checking that the selectors match (...
> > > what am
> > > I missing?). It does check the policies, maybe that is enough in
> > > the
> > > normal IPsec case?
> >
> > The assumption was that identical policies would yield the same
> > SAs,
> > but thats not correct.
>
> Well, to be fair, I think the assumption is valid for normal,
> unlabeled IPsec. The problem comes when SELinux starts labeling SAs
> and now you have multiple SAs for a given policy, each differing only
> in the SELinux/LSM label.
No, it is invalid for normal, unlabeled IPSEC too, in the case where
one has defined xfrm state selectors. That's what my other testsuite
patch (which is presently only on the xfrmselectortest branch) is
exercising - matching of xfrm state selectors. But in any event,
Florian's patch fixes both, so I'm fine with it. I don't know though
how it compares performance-wise with walking the bundle and just
calling security_xfrm_state_pol_flow_match() and xfrm_selector_match()
on each one.
>
> Considering that adding the SELinux/LSM label effectively adds an
> additional selector, I'm wondering if we should simply add the
> SELinux/LSM label matching to xfrm_selector_match()? Looking quickly
> at the code it seems as though we always follow xfrm_selector_match()
> with a LSM check anyway, the one exception being in
> __xfrm_policy_check() ... which *might* be a valid exception, as we
> don't do our access checks for inbound traffic at that point in the
> stack.
Possibly, but that should probably be a separate patch. We should just
fix this regression for 4.14, either via Florian's patch or by
augmenting my patch to perform the matching calls on all of the xfrms.
>
> > > > diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
> > > > index 2746b62..171818b 100644
> > > > --- a/net/xfrm/xfrm_policy.c
> > > > +++ b/net/xfrm/xfrm_policy.c
> > > > @@ -1820,6 +1820,11 @@ xfrm_resolve_and_create_bundle(struct
> > > > xfrm_policy **pols, int num_pols,
> > > > !xfrm_pol_dead(xdst) &&
> > > > memcmp(xdst->pols, pols,
> > > > sizeof(struct xfrm_policy *) * num_pols) ==
> > > > 0 &&
> > > > + (!xdst->u.dst.xfrm->sel.family ||
> > > > + xfrm_selector_match(&xdst->u.dst.xfrm->sel, fl,
> > > > + xdst->u.dst.xfrm->sel.family))
> > > > &&
> > > > + security_xfrm_state_pol_flow_match(xdst-
> > > > >u.dst.xfrm,
> > > > + xdst->pols[0],
> > > > fl) &&
> >
> > ... so this needs to walk the bundle and validate each selector.
> >
> > Alternatively we could always do template resolution and then check
> > that all states found match those of the old pcpu xdst:
> >
> > diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
> > --- a/net/xfrm/xfrm_policy.c
> > +++ b/net/xfrm/xfrm_policy.c
> > @@ -1786,19 +1786,23 @@ void xfrm_policy_cache_flush(void)
> > put_online_cpus();
> > }
> >
> > -static bool xfrm_pol_dead(struct xfrm_dst *xdst)
> > +static bool xfrm_xdst_can_reuse(struct xfrm_dst *xdst,
> > + struct xfrm_state * const xfrm[],
> > + int num)
> > {
> > - unsigned int num_pols = xdst->num_pols;
> > - unsigned int pol_dead = 0, i;
> > + const struct dst_entry *dst = &xdst->u.dst;
> > + int i;
> >
> > - for (i = 0; i < num_pols; i++)
> > - pol_dead |= xdst->pols[i]->walk.dead;
> > + if (xdst->num_xfrms != num)
> > + return false;
> >
> > - /* Mark DST_OBSOLETE_DEAD to fail the next xfrm_dst_check()
> > */
> > - if (pol_dead)
> > - xdst->u.dst.obsolete = DST_OBSOLETE_DEAD;
> > + for (i = 0; i < num; i++) {
> > + if (!dst || dst->xfrm != xfrm[i])
> > + return false;
> > + dst = dst->child;
> > + }
> >
> > - return pol_dead;
> > + return xfrm_bundle_ok(xdst);
> > }
> >
> > static struct xfrm_dst *
> > @@ -1812,26 +1816,28 @@ xfrm_resolve_and_create_bundle(struct
> > xfrm_policy **pols, int num_pols,
> > struct dst_entry *dst;
> > int err;
> >
> > + /* Try to instantiate a bundle */
> > + err = xfrm_tmpl_resolve(pols, num_pols, fl, xfrm, family);
> > + if (err <= 0) {
> > + if (err != 0 && err != -EAGAIN)
> > + XFRM_INC_STATS(net,
> > LINUX_MIB_XFRMOUTPOLERROR);
> > + return ERR_PTR(err);
> > + }
> > +
> > xdst = this_cpu_read(xfrm_last_dst);
> > if (xdst &&
> > xdst->u.dst.dev == dst_orig->dev &&
> > xdst->num_pols == num_pols &&
> > - !xfrm_pol_dead(xdst) &&
> > memcmp(xdst->pols, pols,
> > sizeof(struct xfrm_policy *) * num_pols) == 0 &&
> > - xfrm_bundle_ok(xdst)) {
> > + xfrm_xdst_can_reuse(xdst, xfrm, err)) {
> > dst_hold(&xdst->u.dst);
> > + while (err > 0)
> > + xfrm_state_put(xfrm[--err]);
> > return xdst;
> > }
> >
> > old = xdst;
> > - /* Try to instantiate a bundle */
> > - err = xfrm_tmpl_resolve(pols, num_pols, fl, xfrm, family);
> > - if (err <= 0) {
> > - if (err != 0 && err != -EAGAIN)
> > - XFRM_INC_STATS(net,
> > LINUX_MIB_XFRMOUTPOLERROR);
> > - return ERR_PTR(err);
> > - }
> >
> > dst = xfrm_bundle_create(pols[0], xfrm, err, fl, dst_orig);
> > if (IS_ERR(dst)) {
> > --
> > 2.13.6
>
>
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