Re: git: f9cdaeeeb9ad - main - netinet6: Pass IPv4-mapped ASM multicast joins/leaves to netinet.
Date: Mon, 03 Aug 2026 14:01:39 UTC
On Mon, Aug 03, 2026 at 10:00:18AM -0400, Mark Johnston wrote:
> On Mon, Aug 03, 2026 at 11:28:38AM +0000, Bruce M Simpson wrote:
> > 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));
>
> I'm not sure how this can work: inp_join_group() will invoke
> sooptcopyin() with sopt_val pointing to kernel memory and sopt_td
> non-NULL, so sooptcopyin() will try to copy in from a kernel address and
> inevitably return EFAULT.
I missed your follow up message, sorry for the noise.