net: Create and use new helper xfrm_dst_child().

Only IPSEC routes have a non-NULL dst->child pointer.  And IPSEC
routes are identified by a non-NULL dst->xfrm pointer.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/net/xfrm.h

@@ -994,6 +994,15 @@ struct xfrm_dst {
 	u32 path_cookie;
 };
 
+static inline struct dst_entry *xfrm_dst_child(const struct dst_entry *dst)
+{
+#ifdef CONFIG_XFRM
+	if (dst->xfrm)
+		return dst->child;
+#endif
+	return NULL;
+}
+
 #ifdef CONFIG_XFRM
 static inline void xfrm_dst_destroy(struct xfrm_dst *xdst)
 {

net/core/dst.c

@@ -116,12 +116,14 @@ EXPORT_SYMBOL(dst_alloc);
 
 struct dst_entry *dst_destroy(struct dst_entry * dst)
 {
-	struct dst_entry *child;
+	struct dst_entry *child = NULL;
 
 	smp_rmb();
 
-	child = dst->child;
-
+#ifdef CONFIG_XFRM
+	if (dst->xfrm)
+		child = dst->child;
+#endif
 	if (!(dst->flags & DST_NOCOUNT))
 		dst_entries_add(dst->ops, -1);
 

net/ipv4/xfrm4_mode_tunnel.c

@@ -62,7 +62,7 @@ static int xfrm4_mode_tunnel_output(struct xfrm_state *x, struct sk_buff *skb)
 	top_iph->frag_off = (flags & XFRM_STATE_NOPMTUDISC) ?
 		0 : (XFRM_MODE_SKB_CB(skb)->frag_off & htons(IP_DF));
 
-	top_iph->ttl = ip4_dst_hoplimit(dst->child);
+	top_iph->ttl = ip4_dst_hoplimit(xfrm_dst_child(dst));
 
 	top_iph->saddr = x->props.saddr.a4;
 	top_iph->daddr = x->id.daddr.a4;

net/ipv6/xfrm6_mode_tunnel.c

@@ -59,7 +59,7 @@ static int xfrm6_mode_tunnel_output(struct xfrm_state *x, struct sk_buff *skb)
 	if (x->props.flags & XFRM_STATE_NOECN)
 		dsfield &= ~INET_ECN_MASK;
 	ipv6_change_dsfield(top_iph, 0, dsfield);
-	top_iph->hop_limit = ip6_dst_hoplimit(dst->child);
+	top_iph->hop_limit = ip6_dst_hoplimit(xfrm_dst_child(dst));
 	top_iph->saddr = *(struct in6_addr *)&x->props.saddr;
 	top_iph->daddr = *(struct in6_addr *)&x->id.daddr;
 	return 0;

net/ipv6/xfrm6_policy.c

@@ -265,7 +265,7 @@ static void xfrm6_dst_ifdown(struct dst_entry *dst, struct net_device *dev,
 			in6_dev_put(xdst->u.rt6.rt6i_idev);
 			xdst->u.rt6.rt6i_idev = loopback_idev;
 			in6_dev_hold(loopback_idev);
-			xdst = (struct xfrm_dst *)xdst->u.dst.child;
+			xdst = (struct xfrm_dst *)xfrm_dst_child(&xdst->u.dst);
 		} while (xdst->u.dst.xfrm);
 
 		__in6_dev_put(loopback_idev);

net/xfrm/xfrm_output.c

@@ -44,7 +44,7 @@ static int xfrm_skb_check_space(struct sk_buff *skb)
 
 static struct dst_entry *skb_dst_pop(struct sk_buff *skb)
 {
-	struct dst_entry *child = dst_clone(skb_dst(skb)->child);
+	struct dst_entry *child = dst_clone(xfrm_dst_child(skb_dst(skb)));
 
 	skb_dst_drop(skb);
 	return child;

net/xfrm/xfrm_policy.c

@@ -1636,7 +1636,7 @@ static struct dst_entry *xfrm_bundle_create(struct xfrm_policy *policy,
 	xfrm_init_path((struct xfrm_dst *)dst0, dst, nfheader_len);
 	xfrm_init_pmtu(dst_prev);
 
-	for (dst_prev = dst0; dst_prev != dst; dst_prev = dst_prev->child) {
+	for (dst_prev = dst0; dst_prev != dst; dst_prev = xfrm_dst_child(dst_prev)) {
 		struct xfrm_dst *xdst = (struct xfrm_dst *)dst_prev;
 
 		err = xfrm_fill_dst(xdst, dev, fl);
@@ -1800,7 +1800,7 @@ static bool xfrm_xdst_can_reuse(struct xfrm_dst *xdst,
 	for (i = 0; i < num; i++) {
 		if (!dst || dst->xfrm != xfrm[i])
 			return false;
-		dst = dst->child;
+		dst = xfrm_dst_child(dst);
 	}
 
 	return xfrm_bundle_ok(xdst);
@@ -2576,7 +2576,7 @@ static int stale_bundle(struct dst_entry *dst)
 
 void xfrm_dst_ifdown(struct dst_entry *dst, struct net_device *dev)
 {
-	while ((dst = dst->child) && dst->xfrm && dst->dev == dev) {
+	while ((dst = xfrm_dst_child(dst)) && dst->xfrm && dst->dev == dev) {
 		dst->dev = dev_net(dev)->loopback_dev;
 		dev_hold(dst->dev);
 		dev_put(dev);
@@ -2606,7 +2606,7 @@ static void xfrm_init_pmtu(struct dst_entry *dst)
 		struct xfrm_dst *xdst = (struct xfrm_dst *)dst;
 		u32 pmtu, route_mtu_cached;
 
-		pmtu = dst_mtu(dst->child);
+		pmtu = dst_mtu(xfrm_dst_child(dst));
 		xdst->child_mtu_cached = pmtu;
 
 		pmtu = xfrm_state_mtu(dst->xfrm, pmtu);
@@ -2651,7 +2651,7 @@ static int xfrm_bundle_ok(struct xfrm_dst *first)
 		    xdst->policy_genid != atomic_read(&xdst->pols[0]->genid))
 			return 0;
 
-		mtu = dst_mtu(dst->child);
+		mtu = dst_mtu(xfrm_dst_child(dst));
 		if (xdst->child_mtu_cached != mtu) {
 			last = xdst;
 			xdst->child_mtu_cached = mtu;
@@ -2665,7 +2665,7 @@ static int xfrm_bundle_ok(struct xfrm_dst *first)
 			xdst->route_mtu_cached = mtu;
 		}
 
-		dst = dst->child;
+		dst = xfrm_dst_child(dst);
 	} while (dst->xfrm);
 
 	if (likely(!last))
@@ -2707,7 +2707,7 @@ static const void *xfrm_get_dst_nexthop(const struct dst_entry *dst,
 {
 	const struct dst_entry *path = dst->path;
 
-	for (; dst != path; dst = dst->child) {
+	for (; dst != path; dst = xfrm_dst_child(dst)) {
 		const struct xfrm_state *xfrm = dst->xfrm;
 
 		if (xfrm->props.mode == XFRM_MODE_TRANSPORT)

security/selinux/xfrm.c

@@ -452,7 +452,7 @@ int selinux_xfrm_postroute_last(u32 sk_sid, struct sk_buff *skb,
 	if (dst) {
 		struct dst_entry *iter;
 
-		for (iter = dst; iter != NULL; iter = iter->child) {
+		for (iter = dst; iter != NULL; iter = xfrm_dst_child(iter)) {
 			struct xfrm_state *x = iter->xfrm;
 
 			if (x && selinux_authorizable_xfrm(x))