af_key: Reject optional tunnel/BEET mode templates in outbound policies

xfrm_state_find() uses `encap_family` of the current template with
the passed local and remote addresses to find a matching state.
If an optional tunnel or BEET mode template is skipped in a mixed-family
scenario, there could be a mismatch causing an out-of-bounds read as
the addresses were not replaced to match the family of the next template.

While there are theoretical use cases for optional templates in outbound
policies, the only practical one is to skip IPComp states in inbound
policies if uncompressed packets are received that are handled by an
implicitly created IPIP state instead.

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Signed-off-by: Tobias Brunner <tobias@strongswan.org>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

net/key/af_key.c

@@ -1940,7 +1940,8 @@ static u32 gen_reqid(struct net *net)
 }
 
 static int
-parse_ipsecrequest(struct xfrm_policy *xp, struct sadb_x_ipsecrequest *rq)
+parse_ipsecrequest(struct xfrm_policy *xp, struct sadb_x_policy *pol,
+		   struct sadb_x_ipsecrequest *rq)
 {
 	struct net *net = xp_net(xp);
 	struct xfrm_tmpl *t = xp->xfrm_vec + xp->xfrm_nr;
@@ -1958,9 +1959,12 @@ parse_ipsecrequest(struct xfrm_policy *xp, struct sadb_x_ipsecrequest *rq)
 	if ((mode = pfkey_mode_to_xfrm(rq->sadb_x_ipsecrequest_mode)) < 0)
 		return -EINVAL;
 	t->mode = mode;
-	if (rq->sadb_x_ipsecrequest_level == IPSEC_LEVEL_USE)
+	if (rq->sadb_x_ipsecrequest_level == IPSEC_LEVEL_USE) {
+		if ((mode == XFRM_MODE_TUNNEL || mode == XFRM_MODE_BEET) &&
+		    pol->sadb_x_policy_dir == IPSEC_DIR_OUTBOUND)
+			return -EINVAL;
 		t->optional = 1;
-	else if (rq->sadb_x_ipsecrequest_level == IPSEC_LEVEL_UNIQUE) {
+	} else if (rq->sadb_x_ipsecrequest_level == IPSEC_LEVEL_UNIQUE) {
 		t->reqid = rq->sadb_x_ipsecrequest_reqid;
 		if (t->reqid > IPSEC_MANUAL_REQID_MAX)
 			t->reqid = 0;
@@ -2002,7 +2006,7 @@ parse_ipsecrequests(struct xfrm_policy *xp, struct sadb_x_policy *pol)
 		    rq->sadb_x_ipsecrequest_len < sizeof(*rq))
 			return -EINVAL;
 
-		if ((err = parse_ipsecrequest(xp, rq)) < 0)
+		if ((err = parse_ipsecrequest(xp, pol, rq)) < 0)
 			return err;
 		len -= rq->sadb_x_ipsecrequest_len;
 		rq = (void*)((u8*)rq + rq->sadb_x_ipsecrequest_len);