socket: Fix IPv6 scope id lookup logic to handle another network device problem

The lookup logic preferred to return the last suitable scope id match.
This became a problem if there was already a suitable scope id match before
that was higher in the interface list. This now chooses the higher last
scope id interface match and thus probably in the routing preference.

1 files changed, 12 insertions, 2 deletions

diff --git a/common/socket.c b/common/socket.c
index 749e0ef..a5f9a33 100644
--- a/common/socket.c
+++ b/common/socket.c
@@ -394,11 +394,16 @@ static int32_t _sockaddr_in6_scope_id(struct sockaddr_in6* addr)
 
                 /* use if address is equal */
                 if (memcmp(&addr->sin6_addr.s6_addr, &addr_in->sin6_addr.s6_addr, sizeof(addr_in->sin6_addr.s6_addr)) == 0) {
-                        res = addr_in->sin6_scope_id;
                         /* if scope id equals the requested one then assume it was valid */
                         if (addr->sin6_scope_id == addr_in->sin6_scope_id) {
+                                res = addr_in->sin6_scope_id;
                                 break;
                         } else {
+                                if ((addr_in->sin6_scope_id > addr->sin6_scope_id) && (res >= 0)) {
+                                        // use last valid scope id as we're past the requested scope id
+                                        break;
+                                }
+                                res = addr_in->sin6_scope_id;
                                 continue;
                         }
                 }
@@ -408,11 +413,16 @@ static int32_t _sockaddr_in6_scope_id(struct sockaddr_in6* addr)
                         continue;
                 }
 
-                /* set the scope id of this interface as most likely candidate */
+                if ((addr_in->sin6_scope_id > addr->sin6_scope_id) && (res >= 0)) {
+                        // use last valid scope id as we're past the requested scope id
+                        break;
+                }
+
                 res = addr_in->sin6_scope_id;
 
                 /* if scope id equals the requested one then assume it was valid */
                 if (addr->sin6_scope_id == addr_in->sin6_scope_id) {
+                        /* set the scope id of this interface as most likely candidate */
                         break;
                 }
         }