Fix nodes incorrectly rejecting packets.

Nodes with default mac-verify would not accept packets from nodes with
non-default mac-verify.
Co-authored-by: Julien Muchembled <jm@jmuchemb.eu>
Co-authored-by: Antonin Décimo <antonin.decimo@gmail.com>

hmac.c

@@ -259,6 +259,7 @@ check_hmac(const unsigned char *packet, int packetlen, int bodylen,
 {
     int i = bodylen + 4;
     int len;
+    int rc = -1;
 
     debugf("check_hmac %s -> %s\n",
            format_address(src), format_address(dst));
@@ -278,8 +279,9 @@ check_hmac(const unsigned char *packet, int packetlen, int bodylen,
                               packet + i + 2, len, ifp->key);
             if(ok)
                 return 1;
+            rc = 0;
         }
         i += len + 2;
     }
-    return 0;
+    return rc;
 }

message.c

@@ -608,18 +608,23 @@ parse_packet(const unsigned char *from, struct interface *ifp,
         bodylen = packetlen - 4;
     }
 
-    if(ifp->key != NULL && !(ifp->flags & IF_NO_HMAC_VERIFY)) {
-        if(check_hmac(packet, packetlen, bodylen, from, to, ifp) != 1) {
-            fprintf(stderr, "Received wrong hmac.\n");
+    if(ifp->key != NULL) {
+        switch(check_hmac(packet, packetlen, bodylen, from, to, ifp)) {
+        case -1: /* no mac trailer */
+            if(ifp->flags & IF_NO_HMAC_VERIFY)
+                break;
+            /* fallthrough */
+        case 0:
+            fputs("Received wrong hmac.\n", stderr);
             return;
-        }
-
+        case 1:
             neigh = preparse_packet(packet, bodylen, from, ifp);
             if(neigh == NULL) {
                 fputs("Received wrong PC or failed the challenge.\n", stderr);
                 return;
             }
         }
+    }
 
     neigh = neigh != NULL ? neigh : find_neighbour(from, ifp);
     if(neigh == NULL) {