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Bugfix: Set broadcast address on interface.

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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>
This commit is contained in:
Sebastian Marsching 2025-09-15 13:05:07 +02:00 committed by Gert Doering
parent a69aac41c4
commit 0df0edc49c
2 changed files with 9 additions and 1 deletions
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2
src/openvpn/networking_iproute2.c
View file

@ -150,7 +150,7 @@ net_addr_v4_add(openvpn_net_ctx_t *ctx, const char *iface, const in_addr_t *addr
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, addr_str, prefixlen);
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");

8
src/openvpn/networking_sitnl.c
View file

@ -31,6 +31,7 @@
#include "misc.h"
#include "networking.h"
#include "proto.h"
#include "route.h"
#include <errno.h>
#include <string.h>
@ -803,6 +804,13 @@ 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)
{