nexthop: Expand nexthop_is_multipath in a few places

I got too fancy consolidating checks on multipath type. The result
is that path lookups can access 2 different nh_grp structs as exposed
by Nik's torture tests. Expand nexthop_is_multipath within nexthop.h to
avoid multiple, nh_grp dereferences and make decisions based on the
consistent struct.

Only 2 places left using nexthop_is_multipath are within IPv6, both
only check that the nexthop is a multipath for a branching decision
which are acceptable.

Fixes: 430a0491 ("nexthop: Add support for nexthop groups")
Signed-off-by: David Ahern <dsahern@gmail.com>
Acked-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/nexthop.h

@@ -137,10 +137,11 @@ static inline unsigned int nexthop_num_path(const struct nexthop *nh)
 {
 	unsigned int rc = 1;
 
-	if (nexthop_is_multipath(nh)) {
+	if (nh->is_group) {
 		struct nh_group *nh_grp;
 
 		nh_grp = rcu_dereference_rtnl(nh->nh_grp);
+		if (nh_grp->mpath)
 			rc = nh_grp->num_nh;
 	}
 
@@ -148,10 +149,8 @@ static inline unsigned int nexthop_num_path(const struct nexthop *nh)
 }
 
 static inline
-struct nexthop *nexthop_mpath_select(const struct nexthop *nh, int nhsel)
+struct nexthop *nexthop_mpath_select(const struct nh_group *nhg, int nhsel)
 {
-	const struct nh_group *nhg = rcu_dereference_rtnl(nh->nh_grp);
-
 	/* for_nexthops macros in fib_semantics.c grabs a pointer to
 	 * the nexthop before checking nhsel
 	 */
@@ -186,12 +185,14 @@ static inline bool nexthop_is_blackhole(const struct nexthop *nh)
 {
 	const struct nh_info *nhi;
 
-	if (nexthop_is_multipath(nh)) {
-		if (nexthop_num_path(nh) > 1)
-			return false;
-		nh = nexthop_mpath_select(nh, 0);
-		if (!nh)
+	if (nh->is_group) {
+		struct nh_group *nh_grp;
+
+		nh_grp = rcu_dereference_rtnl(nh->nh_grp);
+		if (nh_grp->num_nh > 1)
 			return false;
+
+		nh = nh_grp->nh_entries[0].nh;
 	}
 
 	nhi = rcu_dereference_rtnl(nh->nh_info);
@@ -217,11 +218,16 @@ struct fib_nh_common *nexthop_fib_nhc(struct nexthop *nh, int nhsel)
 	BUILD_BUG_ON(offsetof(struct fib_nh, nh_common) != 0);
 	BUILD_BUG_ON(offsetof(struct fib6_nh, nh_common) != 0);
 
-	if (nexthop_is_multipath(nh)) {
-		nh = nexthop_mpath_select(nh, nhsel);
+	if (nh->is_group) {
+		struct nh_group *nh_grp;
+
+		nh_grp = rcu_dereference_rtnl(nh->nh_grp);
+		if (nh_grp->mpath) {
+			nh = nexthop_mpath_select(nh_grp, nhsel);
 			if (!nh)
 				return NULL;
 		}
+	}
 
 	nhi = rcu_dereference_rtnl(nh->nh_info);
 	return &nhi->fib_nhc;
@@ -264,8 +270,11 @@ static inline struct fib6_nh *nexthop_fib6_nh(struct nexthop *nh)
 {
 	struct nh_info *nhi;
 
-	if (nexthop_is_multipath(nh)) {
-		nh = nexthop_mpath_select(nh, 0);
+	if (nh->is_group) {
+		struct nh_group *nh_grp;
+
+		nh_grp = rcu_dereference_rtnl(nh->nh_grp);
+		nh = nexthop_mpath_select(nh_grp, 0);
 		if (!nh)
 			return NULL;
 	}