From: Alexander Bluhm <bluhm@openbsd.org>
Subject: Re: Unlock IPV6CTL_USE_DEPRECATED case of ip6_sysctl()
To: Vitaliy Makkoveev <mvs@openbsd.org>
Cc: tech@openbsd.org
Date: Thu, 24 Jul 2025 23:13:52 +0200

On Thu, Jul 24, 2025 at 11:35:36PM +0300, Vitaliy Makkoveev wrote:
> tcp_input() and in6_ifawithscope() belong to input and output path
> respectively. Not used in ramdisk.

OK bluhm@

> Index: sys/netinet/tcp_input.c
> ===================================================================
> RCS file: /cvs/src/sys/netinet/tcp_input.c,v
> retrieving revision 1.456
> diff -u -p -r1.456 tcp_input.c
> --- sys/netinet/tcp_input.c	8 Jul 2025 00:47:41 -0000	1.456
> +++ sys/netinet/tcp_input.c	24 Jul 2025 20:33:13 -0000
> @@ -847,7 +847,8 @@ findpcb:
>  				 * are not exactly the same.  I believe 5.5.4
>  				 * is the best one, so we follow 5.5.4.
>  				 */
> -				if (ip6 && !ip6_use_deprecated) {
> +				if (ip6 &&
> +				    !atomic_load_int(&ip6_use_deprecated)) {
>  					struct in6_ifaddr *ia6;
>  					struct ifnet *ifp =
>  					    if_get(m->m_pkthdr.ph_ifidx);
> Index: sys/netinet6/in6.c
> ===================================================================
> RCS file: /cvs/src/sys/netinet6/in6.c,v
> retrieving revision 1.271
> diff -u -p -r1.271 in6.c
> --- sys/netinet6/in6.c	8 Jul 2025 00:47:41 -0000	1.271
> +++ sys/netinet6/in6.c	24 Jul 2025 20:33:13 -0000
> @@ -1427,7 +1427,7 @@ in6_ifawithscope(struct ifnet *oifp, con
>  				 * Ignore any deprecated addresses if
>  				 * specified by configuration.
>  				 */
> -				if (!ip6_use_deprecated)
> +				if (!atomic_load_int(&ip6_use_deprecated))
>  					continue;
>  
>  				/*
> Index: sys/netinet6/in6_proto.c
> ===================================================================
> RCS file: /cvs/src/sys/netinet6/in6_proto.c,v
> retrieving revision 1.142
> diff -u -p -r1.142 in6_proto.c
> --- sys/netinet6/in6_proto.c	24 Jul 2025 19:49:08 -0000	1.142
> +++ sys/netinet6/in6_proto.c	24 Jul 2025 20:33:13 -0000
> @@ -361,7 +361,7 @@ int	ip6_hdrnestlimit = 10;	/* [a] approp
>  int	ip6_dad_count = 1;	/* [a] DupAddrDetectionTransmits */
>  int	ip6_dad_pending;	/* number of currently running DADs */
>  int	ip6_auto_flowlabel = 1;	/* [a] */
> -int	ip6_use_deprecated = 1;	/* allow deprecated addr (RFC2462 5.5.4) */
> +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_neighborgcthresh = 2048; /* Threshold # of NDP entries for GC */
>  int	ip6_maxdynroutes = 4096; /* Max # of routes created via redirect */
> Index: sys/netinet6/ip6_input.c
> ===================================================================
> RCS file: /cvs/src/sys/netinet6/ip6_input.c,v
> retrieving revision 1.286
> diff -u -p -r1.286 ip6_input.c
> --- sys/netinet6/ip6_input.c	24 Jul 2025 19:49:08 -0000	1.286
> +++ sys/netinet6/ip6_input.c	24 Jul 2025 20:33:13 -0000
> @@ -1453,10 +1453,10 @@ const struct sysctl_bounded_args ipv6ctl
>  	{ IPV6CTL_DAD_COUNT, &ip6_dad_count, 0, 10 },
>  	{ IPV6CTL_AUTO_FLOWLABEL, &ip6_auto_flowlabel, 0, 1 },
>  	{ IPV6CTL_DEFMCASTHLIM, &ip6_defmcasthlim, 0, 255 },
> +	{ IPV6CTL_USE_DEPRECATED, &ip6_use_deprecated, 0, 1 },
>  };
>  
>  const struct sysctl_bounded_args ipv6ctl_vars[] = {
> -	{ 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 },
> @@ -1576,6 +1576,7 @@ ip6_sysctl(int *name, u_int namelen, voi
>  	case IPV6CTL_DAD_COUNT:
>  	case IPV6CTL_AUTO_FLOWLABEL:
>  	case IPV6CTL_DEFMCASTHLIM:
> +	case IPV6CTL_USE_DEPRECATED:
>  		return (sysctl_bounded_arr(
>  		    ipv6ctl_vars_unlocked, nitems(ipv6ctl_vars_unlocked),
>  		    name, namelen, oldp, oldlenp, newp, newlen));