git: f9cdaeeeb9ad - main - netinet6: Pass IPv4-mapped ASM multicast joins/leaves to netinet.
Date: Mon, 03 Aug 2026 11:28:38 UTC
The branch main has been updated by bms:
URL: https://cgit.FreeBSD.org/src/commit/?id=f9cdaeeeb9ad45a5e8c0cd32ff9443d245b64185
commit f9cdaeeeb9ad45a5e8c0cd32ff9443d245b64185
Author: Bruce M Simpson <bms@FreeBSD.org>
AuthorDate: 2026-08-01 10:14:57 +0000
Commit: Bruce M Simpson <bms@FreeBSD.org>
CommitDate: 2026-08-03 11:27:45 +0000
netinet6: Pass IPv4-mapped ASM multicast joins/leaves to netinet.
Add support for allowing IPv4 multicast groups to be joined on IPv6 sockets,
as a number of applications began to rely on this over the years, despite it
only ever having been a convenience which appeared in Solaris & Linux over
the course of the 00s decade. It is limited to any-source joins (ASM).
To avoid further quibbling over the meaning of the term "undocumented" as it
applies to this change, I have chosen to use the wording "non-IETF-ratified
extension" in comments, with reference to the updated ip6(4) man page.
PR: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=193246
---
sys/netinet/in_mcast.c | 6 +--
sys/netinet/in_var.h | 5 +++
sys/netinet6/in6_mcast.c | 112 ++++++++++++++++++++++++++++++++++++++++++++++-
3 files changed, 118 insertions(+), 5 deletions(-)
diff --git a/sys/netinet/in_mcast.c b/sys/netinet/in_mcast.c
index 934cc71e745b..ad908b72c340 100644
--- a/sys/netinet/in_mcast.c
+++ b/sys/netinet/in_mcast.c
@@ -158,8 +158,6 @@ static void inm_release(struct in_multi *);
static struct ip_moptions *
inp_findmoptions(struct inpcb *);
static int inp_get_source_filters(struct inpcb *, struct sockopt *);
-static int inp_join_group(struct inpcb *, struct sockopt *);
-static int inp_leave_group(struct inpcb *, struct sockopt *);
static int inp_block_unblock_source(struct inpcb *, struct sockopt *);
static int inp_set_multicast_if(struct inpcb *, struct sockopt *);
static int inp_set_source_filters(struct inpcb *, struct sockopt *);
@@ -1884,7 +1882,7 @@ const struct in_addr *ina, const u_int index)
/*
* Join an IPv4 multicast group, possibly with a source.
*/
-static int
+int
inp_join_group(struct inpcb *inp, struct sockopt *sopt)
{
struct group_source_req gsr;
@@ -2208,7 +2206,7 @@ out_inp_unlocked:
/*
* Leave an IPv4 multicast group on an inpcb, possibly with a source.
*/
-static int
+int
inp_leave_group(struct inpcb *inp, struct sockopt *sopt)
{
struct epoch_tracker et;
diff --git a/sys/netinet/in_var.h b/sys/netinet/in_var.h
index 99a628477155..e9db1efd9fe9 100644
--- a/sys/netinet/in_var.h
+++ b/sys/netinet/in_var.h
@@ -459,6 +459,11 @@ void in_ifattach(void *, struct ifnet *);
void in_detachhead(struct rib_head *rh);
#endif
+struct sockopt;
+
+int inp_join_group(struct inpcb *, struct sockopt *);
+int inp_leave_group(struct inpcb *, struct sockopt *);
+
#endif /* _KERNEL */
/* INET6 stuff */
diff --git a/sys/netinet6/in6_mcast.c b/sys/netinet6/in6_mcast.c
index fad47cb0e69b..a204ad88a9a5 100644
--- a/sys/netinet6/in6_mcast.c
+++ b/sys/netinet6/in6_mcast.c
@@ -1,7 +1,7 @@
/*-
* SPDX-License-Identifier: BSD-3-Clause
*
- * Copyright (c) 2009 Bruce Simpson.
+ * Copyright (c) 2009-2026 Bruce Simpson.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
@@ -34,6 +34,7 @@
* Normative references: RFC 2292, RFC 3492, RFC 3542, RFC 3678, RFC 3810.
*/
+#include "opt_inet.h"
#include "opt_inet6.h"
#include <sys/param.h>
@@ -162,6 +163,9 @@ static struct ifnet *
static int in6p_block_unblock_source(struct inpcb *, struct sockopt *);
static int in6p_set_multicast_if(struct inpcb *, struct sockopt *);
static int in6p_set_source_filters(struct inpcb *, struct sockopt *);
+#ifdef INET
+static int in6_v6_mreq_to_v4(struct ipv6_mreq *, struct ip_mreq *);
+#endif
static int sysctl_ip6_mcast_filters(SYSCTL_HANDLER_ARGS);
SYSCTL_DECL(_net_inet6_ip6); /* XXX Not in any common header. */
@@ -1881,6 +1885,54 @@ in6p_lookup_mcast_ifp(const struct inpcb *inp, const struct sockaddr_in6 *gsin6)
return (nh ? nh->nh_ifp : NULL);
}
+#ifdef INET
+/*
+ * Perform sockopt mreq argument conversion for IPv4-mapped groups.
+ *
+ * This function is required to support an extension to the behaviour
+ * in RFC 3493 Sec 3.7, which was never formally proposed by any
+ * contemporary IPv6 normative reference, but which is now required
+ * by much application software using IPv6 sockets as a convenience.
+ * Refer to manual page ip6(4) for further information.
+ *
+ * FUTURE: Use IPv4 source-address selection.
+ */
+static int
+in6_v6_mreq_to_v4(struct ipv6_mreq *mreq, struct ip_mreq *mreq_v4)
+{
+ int error;
+ struct epoch_tracker et;
+ struct ifnet *ifp;
+ struct in_ifaddr *ia;
+
+ NET_EPOCH_ENTER(et);
+
+ ifp = ifnet_byindex(mreq->ipv6mr_interface);
+ if (ifp == NULL) {
+ error = EADDRNOTAVAIL;
+ goto out;
+ }
+
+ /*
+ * Here, we do not compare the ifnet's primary IPv4 address with
+ * INADDR_ANY, to permit its use during system initialization.
+ * If this is not required, an appropriate check to screen it out
+ * should be added, e.g. in_nullhost(ia->ia_addr.sin_addr.s_addr).
+ */
+ ia = in_ifprimaryaddr(ifp);
+ if (ia == NULL) {
+ error = EADDRNOTAVAIL;
+ goto out;
+ }
+ mreq_v4->imr_interface.s_addr = IA_SIN(ia)->sin_addr.s_addr;
+ error = 0;
+
+out:
+ NET_EPOCH_EXIT(et);
+ return (error);
+}
+#endif /* INET */
+
/*
* Join an IPv6 multicast group, possibly with a source.
*
@@ -1929,6 +1981,35 @@ in6p_join_group(struct inpcb *inp, struct sockopt *sopt)
sizeof(struct ipv6_mreq));
if (error)
return (error);
+#ifdef INET
+ /*
+ * Support for the non-IETF-ratified extension to RFC 3493 to
+ * join IPv4 groups as IPv4 mapped addresses on IPv6 sockets.
+ */
+ if (IN6_IS_ADDR_V4MAPPED(&mreq.ipv6mr_multiaddr)) {
+ struct ip_mreq mreq_v4;
+ struct sockopt sopt_v4 = {
+ .sopt_dir = SOPT_SET,
+ .sopt_level = sopt->sopt_level,
+ .sopt_name = IP_ADD_MEMBERSHIP,
+ .sopt_val = &mreq_v4,
+ .sopt_valsize = sizeof(mreq_v4),
+ .sopt_rights = sopt->sopt_rights,
+ .sopt_td = sopt->sopt_td
+ };
+
+ mreq_v4.imr_multiaddr.s_addr =
+ mreq.ipv6mr_multiaddr.s6_addr32[3];
+ if (mreq.ipv6mr_interface == 0)
+ mreq_v4.imr_interface.s_addr = INADDR_ANY;
+ else
+ error = in6_v6_mreq_to_v4(&mreq, &mreq_v4);
+ if (error)
+ return error;
+
+ return (inp_join_group(inp, &sopt_v4));
+ }
+#endif /* INET */
gsa->sin6.sin6_family = AF_INET6;
gsa->sin6.sin6_len = sizeof(struct sockaddr_in6);
@@ -2242,6 +2323,35 @@ in6p_leave_group(struct inpcb *inp, struct sockopt *sopt)
sizeof(struct ipv6_mreq));
if (error)
return (error);
+#ifdef INET
+ /*
+ * Support for the non-IETF-ratified extension to RFC 3493 to
+ * leave IPv4 groups as IPv4 mapped addresses on IPv6 sockets.
+ */
+ if (IN6_IS_ADDR_V4MAPPED(&mreq.ipv6mr_multiaddr)) {
+ struct ip_mreq mreq_v4;
+ struct sockopt sopt_v4 = {
+ .sopt_dir = SOPT_SET,
+ .sopt_level = sopt->sopt_level,
+ .sopt_name = IP_DROP_MEMBERSHIP,
+ .sopt_val = &mreq_v4,
+ .sopt_valsize = sizeof(mreq_v4),
+ .sopt_rights = sopt->sopt_rights,
+ .sopt_td = sopt->sopt_td
+ };
+
+ mreq_v4.imr_multiaddr.s_addr =
+ mreq.ipv6mr_multiaddr.s6_addr32[3];
+ if (mreq.ipv6mr_interface == 0)
+ mreq_v4.imr_interface.s_addr = INADDR_ANY;
+ else
+ error = in6_v6_mreq_to_v4(&mreq, &mreq_v4);
+ if (error)
+ return error;
+
+ return (inp_leave_group(inp, &sopt_v4));
+ }
+#endif /* INET */
gsa->sin6.sin6_family = AF_INET6;
gsa->sin6.sin6_len = sizeof(struct sockaddr_in6);
gsa->sin6.sin6_addr = mreq.ipv6mr_multiaddr;