From: Alexander Bluhm <bluhm@openbsd.org>
Subject: Re: Unlock IPV6CTL_MCAST_PMTU case of ip6_sysctl()
To: Vitaliy Makkoveev <mvs@openbsd.org>
Cc: tech@openbsd.org
Date: Sat, 26 Jul 2025 00:13:58 +0200

On Fri, Jul 25, 2025 at 11:40:22PM +0300, Vitaliy Makkoveev wrote:
> Cache `ip6_mcast_pmtu' value and pass it to phyint_send6().
> Not used in ramdisk.

OK bluhm@

> Index: sys/netinet6/in6_proto.c
> ===================================================================
> RCS file: /cvs/src/sys/netinet6/in6_proto.c,v
> retrieving revision 1.145
> diff -u -p -r1.145 in6_proto.c
> --- sys/netinet6/in6_proto.c	25 Jul 2025 20:04:47 -0000	1.145
> +++ sys/netinet6/in6_proto.c	25 Jul 2025 20:37:05 -0000
> @@ -362,7 +362,7 @@ int	ip6_dad_count = 1;	/* [a] DupAddrDet
>  int	ip6_dad_pending;	/* number of currently running DADs */
>  int	ip6_auto_flowlabel = 1;	/* [a] */
>  int	ip6_use_deprecated = 1;	/* [a] allow deprecated addr (RFC2462 5.5.4) */
> -int	ip6_mcast_pmtu = 0;	/* enable pMTU discovery for multicast? */
> +int	ip6_mcast_pmtu = 0;	/* [a] enable pMTU discovery for multicast? */
>  int	ip6_neighborgcthresh = 2048; /* Threshold # of NDP entries for GC */
>  int	ip6_maxdynroutes = 4096; /* Max # of routes created via redirect */
>  time_t	ip6_log_time = (time_t)0L;
> Index: sys/netinet6/ip6_input.c
> ===================================================================
> RCS file: /cvs/src/sys/netinet6/ip6_input.c,v
> retrieving revision 1.290
> diff -u -p -r1.290 ip6_input.c
> --- sys/netinet6/ip6_input.c	25 Jul 2025 20:04:47 -0000	1.290
> +++ sys/netinet6/ip6_input.c	25 Jul 2025 20:37:05 -0000
> @@ -1457,10 +1457,10 @@ const struct sysctl_bounded_args ipv6ctl
>  	{ IPV6CTL_USE_DEPRECATED, &ip6_use_deprecated, 0, 1 },
>  	{ IPV6CTL_MAXFRAGS, &ip6_maxfrags, 0, 1000 },
>  	{ IPV6CTL_MFORWARDING, &ip6_mforwarding, 0, 1 },
> +	{ IPV6CTL_MCAST_PMTU, &ip6_mcast_pmtu, 0, 1 },
>  };
>  
>  const struct sysctl_bounded_args ipv6ctl_vars[] = {
> -	{ IPV6CTL_MCAST_PMTU, &ip6_mcast_pmtu, 0, 1 },
>  	{ IPV6CTL_NEIGHBORGCTHRESH, &ip6_neighborgcthresh, -1, 5 * 2048 },
>  	{ IPV6CTL_MAXDYNROUTES, &ip6_maxdynroutes, -1, 5 * 4096 },
>  };
> @@ -1577,6 +1577,7 @@ ip6_sysctl(int *name, u_int namelen, voi
>  	case IPV6CTL_USE_DEPRECATED:
>  	case IPV6CTL_MAXFRAGS:
>  	case IPV6CTL_MFORWARDING:
> +	case IPV6CTL_MCAST_PMTU:
>  		return (sysctl_bounded_arr(
>  		    ipv6ctl_vars_unlocked, nitems(ipv6ctl_vars_unlocked),
>  		    name, namelen, oldp, oldlenp, newp, newlen));
> Index: sys/netinet6/ip6_mroute.c
> ===================================================================
> RCS file: /cvs/src/sys/netinet6/ip6_mroute.c,v
> retrieving revision 1.152
> diff -u -p -r1.152 ip6_mroute.c
> --- sys/netinet6/ip6_mroute.c	24 Jul 2025 21:35:53 -0000	1.152
> +++ sys/netinet6/ip6_mroute.c	25 Jul 2025 20:37:05 -0000
> @@ -125,7 +125,7 @@ int mcast6_debug = 1;
>  #endif
>  
>  int ip6_mdq(struct mbuf *, struct ifnet *, struct rtentry *, int);
> -void phyint_send6(struct ifnet *, struct ip6_hdr *, struct mbuf *, int);
> +void phyint_send6(struct ifnet *, struct ip6_hdr *, struct mbuf *, int, int);
>  
>  /*
>   * Globals.  All but ip6_mrouter, ip6_mrtproto and mrt6stat could be static,
> @@ -1078,7 +1078,7 @@ ip6_mdq(struct mbuf *m, struct ifnet *if
>  	struct mif6 *m6, *mifp = (struct mif6 *)ifp->if_mcast6;
>  	struct mf6c *mf6c = (struct mf6c *)rt->rt_llinfo;
>  	struct ifnet *ifn;
> -	int plen = m->m_pkthdr.len;
> +	int plen = m->m_pkthdr.len, ip6_mcast_pmtu_local;
>  
>  	if (mifp == NULL || mf6c == NULL) {
>  		rtfree(rt);
> @@ -1111,6 +1111,8 @@ ip6_mdq(struct mbuf *m, struct ifnet *if
>  	 * For each mif, forward a copy of the packet if there are group
>  	 * members downstream on the interface.
>  	 */
> +	ip6_mcast_pmtu_local = atomic_load_int(&ip6_mcast_pmtu);
> +
>  	do {
>  		/* Don't consider non multicast routes. */
>  		if (ISSET(rt->rt_flags, RTF_HOST | RTF_MULTICAST) !=
> @@ -1160,7 +1162,7 @@ ip6_mdq(struct mbuf *m, struct ifnet *if
>  		m6->m6_pkt_out++;
>  		m6->m6_bytes_out += plen;
>  
> -		phyint_send6(ifn, ip6, m, flags);
> +		phyint_send6(ifn, ip6, m, flags, ip6_mcast_pmtu_local);
>  		if_put(ifn);
>  	} while ((rt = rtable_iterate(rt)) != NULL);
>  
> @@ -1168,7 +1170,8 @@ ip6_mdq(struct mbuf *m, struct ifnet *if
>  }
>  
>  void
> -phyint_send6(struct ifnet *ifp, struct ip6_hdr *ip6, struct mbuf *m, int flags)
> +phyint_send6(struct ifnet *ifp, struct ip6_hdr *ip6, struct mbuf *m,
> +    int flags, int mcast_pmtu)
>  {
>  	struct mbuf *mb_copy;
>  	struct sockaddr_in6 *dst6, sin6;
> @@ -1228,7 +1231,7 @@ phyint_send6(struct ifnet *ifp, struct i
>  		dst6->sin6_addr = ip6->ip6_dst;
>  		error = ifp->if_output(ifp, mb_copy, sin6tosa(dst6), NULL);
>  	} else {
> -		if (ip6_mcast_pmtu)
> +		if (mcast_pmtu)
>  			icmp6_error(mb_copy, ICMP6_PACKET_TOO_BIG, 0,
>  			    ifp->if_mtu);
>  		else {