From: Sebastian Marsching <sebastian-git-2016@marsching.com>
Date: Mon, 15 Sep 2025 11:05:07 +0000 (+0200)
Subject: Bugfix: Set broadcast address on interface.
X-Git-Tag: v2.6.15~2
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=4e46e727217cf58c7c671e36e8417e469c4e3b1d;p=thirdparty%2Fopenvpn.git

Bugfix: Set broadcast address on interface.

This fixes a problem that was introduced in OpenVPN 2.5. Previously,
the ifconfig utility was used for adding the local address to an
interface. This utility automatically sets the correct broadcast address
based on the given unicast address and netmask.

Due to switching to iproute and Netlink, this does not happen
automatically any longer, which means that applications that rely on
broadcasts do not work correctly.

This patch fixes this issue both when using iproute (by telling iproute
to set the broadcast address based on the local address and prefix) and
when using Netlink (by calculating the correct broadcast address and
setting it).

Signed-off-by: Sebastian Marsching <sebastian-git-2016@marsching.com>
Acked-by: Antonio Quartulli <antonio@openvpn.net>
Message-Id: <20250915110507.20557-1-sebastian-git-2016@marsching.com>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg33131.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit 0df0edc49ce4acb96c8e16bdf0fcee1eedfd91f0)
---

diff --git a/src/openvpn/networking_iproute2.c b/src/openvpn/networking_iproute2.c
index 975282ca1..74ddc2415 100644
--- a/src/openvpn/networking_iproute2.c
+++ b/src/openvpn/networking_iproute2.c
@@ -159,7 +159,7 @@ net_addr_v4_add(openvpn_net_ctx_t *ctx, const char *iface,
 
     const char *addr_str = print_in_addr_t(*addr, 0, &ctx->gc);
 
-    argv_printf(&argv, "%s addr add dev %s %s/%d", iproute_path, iface,
+    argv_printf(&argv, "%s addr add dev %s %s/%d broadcast +", iproute_path, iface,
                 addr_str, prefixlen);
     argv_msg(M_INFO, &argv);
     openvpn_execve_check(&argv, ctx->es, S_FATAL, "Linux ip addr add failed");
diff --git a/src/openvpn/networking_sitnl.c b/src/openvpn/networking_sitnl.c
index f53f5ee9e..10c382562 100644
--- a/src/openvpn/networking_sitnl.c
+++ b/src/openvpn/networking_sitnl.c
@@ -32,6 +32,7 @@
 #include "misc.h"
 #include "networking.h"
 #include "proto.h"
+#include "route.h"
 
 #include <errno.h>
 #include <string.h>
@@ -800,6 +801,13 @@ sitnl_addr_set(int cmd, uint32_t flags, int ifindex, sa_family_t af_family,
         SITNL_ADDATTR(&req.n, sizeof(req), IFA_LOCAL, local, size);
     }
 
+    if (af_family == AF_INET && local && !remote && prefixlen <= 30)
+    {
+        inet_address_t broadcast = *local;
+        broadcast.ipv4 |= htonl(~netbits_to_netmask(prefixlen));
+        SITNL_ADDATTR(&req.n, sizeof(req), IFA_BROADCAST, &broadcast, size);
+    }
+
     ret = sitnl_send(&req.n, 0, 0, NULL, NULL);
     if (ret == -EEXIST)
     {