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Message-ID: <CAHC9VhT7FOeoJgX=KmMPr_ACKSgJ8V9DEHNM=cnfV9-sdrHC2g@mail.gmail.com>
Date: Wed, 1 Nov 2017 17:39:31 -0400
From: Paul Moore <paul@...l-moore.com>
To: Florian Westphal <fw@...len.de>
Cc: Stephen Smalley <sds@...ho.nsa.gov>, netdev@...r.kernel.org,
linux-security-module@...r.kernel.org, selinux@...ho.nsa.gov,
davem@...emloft.net, herbert@...dor.apana.org.au,
steffen.klassert@...unet.com
Subject: Re: [RFC PATCH] xfrm: fix regression introduced by xdst pcpu cache
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.
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.
>> > 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
--
paul moore
www.paul-moore.com
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