From 23486b312c0dd9c147799d5f312c0b9ac015eec3 Mon Sep 17 00:00:00 2001
From: flu0r1ne <flu0r1ne@flu0r1ne.net>
Date: Tue, 3 Oct 2023 22:31:23 -0500
Subject: [PATCH] Use Packet Marking for IP Address Selection

In certain scenarios, the routing policy database may affect packet
routing. When selecting an address in `mtr`, assign a packet mark if
`SO_MARK` is defined and a mark has been supplied.
---
 ui/net.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/ui/net.c b/ui/net.c
index efeb782..45c33ec 100644
--- a/ui/net.c
+++ b/ui/net.c
@@ -687,8 +687,8 @@ static void net_find_interface_address_from_name(
   host by connecting a UDP socket and checking the address
   the socket is bound to.
 */
-static void net_find_local_address(
-    void)
+static
+void net_find_local_address(struct mtr_ctl * ctl)
 {
     int udp_socket;
     int addr_length;
@@ -700,6 +700,15 @@ static void net_find_local_address(
         error(EXIT_FAILURE, errno, "udp socket creation failed");
     }
 
+#ifdef SO_MARK
+    /* On Linux, the packet mark can affect the selection of the source address */
+    if(ctl->mark) {
+        if(setsockopt(udp_socket, SOL_SOCKET, SO_MARK, &ctl->mark, sizeof(ctl->mark))) {
+            error(EXIT_FAILURE, errno, "failed to set the packet mark");
+        }
+    }
+#endif
+
     /*
        We need to set the port to a non-zero value for the connect
        to succeed.
@@ -778,7 +787,7 @@ void net_reopen(
             &sourcesockaddr_struct, ctl->af, ctl->InterfaceName);
         inet_ntop(sourcesockaddr->sa_family, sourceaddress, localaddr, sizeof(localaddr));
     } else {
-        net_find_local_address();
+        net_find_local_address(ctl);
     }
 
 }