Fix failure to add an interface prefix route when route with the same

prefix is already presented in the routing table.

PR:		277125
Reported by:	Oleksandr Ignatyev <alex@i.org.ua>
Reviewed by:	ae, jlduran
Tested by:	jlduran
Differential Revision: https://reviews.freebsd.org/D47534
MFC after:	2 weeks

sys/net/route/route_ctl.c

@@ -772,12 +772,15 @@ add_route_byinfo(struct rib_head *rnh, struct rt_addrinfo *info,
 	rnd_add.rnd_weight = get_info_weight(info, RT_DEFAULT_WEIGHT);
 
 	int op_flags = RTM_F_CREATE;
-	if (get_prio_from_info(info) == NH_PRIORITY_HIGH)
-		op_flags |= RTM_F_FORCE;
-	else
-		op_flags |= RTM_F_APPEND;
-	return (add_route_flags(rnh, rt, &rnd_add, op_flags, rc));
 
+	/*
+	 * Set the desired action when the route already exists:
+	 * If RTF_PINNED is present, assume the direct kernel routes that cannot be multipath.
+	 * Otherwise, append the path.
+	 */
+	op_flags |= (info->rti_flags & RTF_PINNED) ? RTM_F_REPLACE : RTM_F_APPEND;
+
+	return (add_route_flags(rnh, rt, &rnd_add, op_flags, rc));
 }
 
 static int

sys/net/route/route_ctl.h

@@ -61,11 +61,11 @@ int rib_del_route_px_gw(uint32_t fibnum, struct sockaddr *dst, int plen,
     const struct sockaddr *gw, int op_flags, struct rib_cmd_info *rc);
 
 /* operation flags */
-#define	RTM_F_CREATE	0x01
+#define	RTM_F_CREATE	0x01	/* Create object if not exists */
-#define	RTM_F_EXCL	0x02
+#define	RTM_F_EXCL	0x02	/* (Deprecated) Do not replace or append if exists */
-#define	RTM_F_REPLACE	0x04
+#define	RTM_F_REPLACE	0x04	/* Replace if route (even multipath) if exists */
-#define	RTM_F_APPEND	0x08
+#define	RTM_F_APPEND	0x08	/* Append path to the route */
-#define	RTM_F_FORCE	0x10
+#define	RTM_F_FORCE	0x10	/* Bump operation priority to highest */
 
 int rib_add_route(uint32_t fibnum, struct rt_addrinfo *info,
   struct rib_cmd_info *rc);