[XFRM] IPV6: Restrict bundle reusing

For outbound transformation, bundle is checked whether it is
suitable for current flow to be reused or not. In such IPv6 case
as below, transformation may apply incorrect bundle for the flow instead
of creating another bundle:

- The policy selector has destination prefix length < 128
  (Two or more addresses can be matched it)
- Its bundle holds dst entry of default route whose prefix length < 128
  (Previous traffic was used such route as next hop)
- The policy and the bundle were used a transport mode state and
  this time flow address is not matched the bundled state.

This issue is found by Mobile IPv6 usage to protect mobility signaling
by IPsec, but it is not a Mobile IPv6 specific.
This patch adds strict check to xfrm_bundle_ok() for each
state mode and address when prefix length is less than 128.
Signed-off-by: Masahide NAKAMURA <nakam@linux-ipv6.org>
Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/xfrm.h

@@ -869,6 +869,23 @@ xfrm_state_addr_check(struct xfrm_state *x,
 	return 0;
 }
 
+static __inline__ int
+xfrm_state_addr_flow_check(struct xfrm_state *x, struct flowi *fl,
+			   unsigned short family)
+{
+	switch (family) {
+	case AF_INET:
+		return __xfrm4_state_addr_check(x,
+						(xfrm_address_t *)&fl->fl4_dst,
+						(xfrm_address_t *)&fl->fl4_src);
+	case AF_INET6:
+		return __xfrm6_state_addr_check(x,
+						(xfrm_address_t *)&fl->fl6_dst,
+						(xfrm_address_t *)&fl->fl6_src);
+	}
+	return 0;
+}
+
 static inline int xfrm_state_kern(struct xfrm_state *x)
 {
 	return atomic_read(&x->tunnel_users);
@@ -1014,7 +1031,7 @@ extern void xfrm_policy_flush(void);
 extern int xfrm_sk_policy_insert(struct sock *sk, int dir, struct xfrm_policy *pol);
 extern int xfrm_flush_bundles(void);
 extern void xfrm_flush_all_bundles(void);
-extern int xfrm_bundle_ok(struct xfrm_dst *xdst, struct flowi *fl, int family);
+extern int xfrm_bundle_ok(struct xfrm_dst *xdst, struct flowi *fl, int family, int strict);
 extern void xfrm_init_pmtu(struct dst_entry *dst);
 
 extern wait_queue_head_t km_waitq;

net/ipv4/xfrm4_policy.c

@@ -33,7 +33,7 @@ __xfrm4_find_bundle(struct flowi *fl, struct xfrm_policy *policy)
 		    xdst->u.rt.fl.fl4_dst == fl->fl4_dst &&
 	    	    xdst->u.rt.fl.fl4_src == fl->fl4_src &&
 	    	    xdst->u.rt.fl.fl4_tos == fl->fl4_tos &&
-		    xfrm_bundle_ok(xdst, fl, AF_INET)) {
+		    xfrm_bundle_ok(xdst, fl, AF_INET, 0)) {
 			dst_clone(dst);
 			break;
 		}

net/ipv6/xfrm6_policy.c

@@ -50,7 +50,9 @@ __xfrm6_find_bundle(struct flowi *fl, struct xfrm_policy *policy)
 				 xdst->u.rt6.rt6i_src.plen);
 		if (ipv6_addr_equal(&xdst->u.rt6.rt6i_dst.addr, &fl_dst_prefix) &&
 		    ipv6_addr_equal(&xdst->u.rt6.rt6i_src.addr, &fl_src_prefix) &&
-		    xfrm_bundle_ok(xdst, fl, AF_INET6)) {
+		    xfrm_bundle_ok(xdst, fl, AF_INET6,
+				   (xdst->u.rt6.rt6i_dst.plen != 128 ||
+				    xdst->u.rt6.rt6i_src.plen != 128))) {
 			dst_clone(dst);
 			break;
 		}

net/xfrm/xfrm_policy.c

@@ -1167,7 +1167,7 @@ static struct dst_entry *xfrm_dst_check(struct dst_entry *dst, u32 cookie)
 
 static int stale_bundle(struct dst_entry *dst)
 {
-	return !xfrm_bundle_ok((struct xfrm_dst *)dst, NULL, AF_UNSPEC);
+	return !xfrm_bundle_ok((struct xfrm_dst *)dst, NULL, AF_UNSPEC, 0);
 }
 
 void xfrm_dst_ifdown(struct dst_entry *dst, struct net_device *dev)
@@ -1282,7 +1282,7 @@ EXPORT_SYMBOL(xfrm_init_pmtu);
  * still valid.
  */
 
-int xfrm_bundle_ok(struct xfrm_dst *first, struct flowi *fl, int family)
+int xfrm_bundle_ok(struct xfrm_dst *first, struct flowi *fl, int family, int strict)
 {
 	struct dst_entry *dst = &first->u.dst;
 	struct xfrm_dst *last;
@@ -1304,6 +1304,10 @@ int xfrm_bundle_ok(struct xfrm_dst *first, struct flowi *fl, int family)
 		if (dst->xfrm->km.state != XFRM_STATE_VALID)
 			return 0;
 
+		if (strict && fl && dst->xfrm->props.mode != XFRM_MODE_TUNNEL &&
+		    !xfrm_state_addr_flow_check(dst->xfrm, fl, family))
+			return 0;
+
 		mtu = dst_mtu(dst->child);
 		if (xdst->child_mtu_cached != mtu) {
 			last = xdst;