From: Alexander Bluhm <bluhm@openbsd.org>
Subject: Re: Unlock IPV6CTL_DAD_COUNT case of ip6_sysctl()
To: Vitaliy Makkoveev <mvs@openbsd.org>
Cc: tech@openbsd.org
Date: Thu, 24 Jul 2025 00:02:31 +0200

On Thu, Jul 24, 2025 at 12:41:18AM +0300, Vitaliy Makkoveev wrote:
> `ip6_dad_count' is local to nd6_dad_start() and used only to initialize
> `dad_count' of the addresses to run DAD on. However, we do non-null
> check before, so use cached value. Unused in ramdisk.

OK bluhm@

> Index: sys/netinet6/in6_proto.c
> ===================================================================
> RCS file: /cvs/src/sys/netinet6/in6_proto.c,v
> retrieving revision 1.139
> diff -u -p -r1.139 in6_proto.c
> --- sys/netinet6/in6_proto.c	23 Jul 2025 20:53:55 -0000	1.139
> +++ sys/netinet6/in6_proto.c	23 Jul 2025 21:35:35 -0000
> @@ -358,7 +358,7 @@ int	ip6_maxfragpackets = 200;	/* [a] */
>  int	ip6_maxfrags = 200;
>  int	ip6_log_interval = 5;	/* [a] */
>  int	ip6_hdrnestlimit = 10;	/* [a] appropriate? */
> -int	ip6_dad_count = 1;	/* DupAddrDetectionTransmits */
> +int	ip6_dad_count = 1;	/* [a] DupAddrDetectionTransmits */
>  int	ip6_dad_pending;	/* number of currently running DADs */
>  int	ip6_auto_flowlabel = 1;
>  int	ip6_use_deprecated = 1;	/* allow deprecated addr (RFC2462 5.5.4) */
> Index: sys/netinet6/ip6_input.c
> ===================================================================
> RCS file: /cvs/src/sys/netinet6/ip6_input.c,v
> retrieving revision 1.283
> diff -u -p -r1.283 ip6_input.c
> --- sys/netinet6/ip6_input.c	23 Jul 2025 20:53:55 -0000	1.283
> +++ sys/netinet6/ip6_input.c	23 Jul 2025 21:35:35 -0000
> @@ -1450,10 +1450,10 @@ const struct sysctl_bounded_args ipv6ctl
>  	{ IPV6CTL_MAXFRAGPACKETS, &ip6_maxfragpackets, 0, 1000 },
>  	{ IPV6CTL_LOG_INTERVAL, &ip6_log_interval, 0, INT_MAX },
>  	{ IPV6CTL_HDRNESTLIMIT, &ip6_hdrnestlimit, 0, 100 },
> +	{ IPV6CTL_DAD_COUNT, &ip6_dad_count, 0, 10 },
>  };
>  
>  const struct sysctl_bounded_args ipv6ctl_vars[] = {
> -	{ 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 },
> @@ -1573,6 +1573,7 @@ ip6_sysctl(int *name, u_int namelen, voi
>  	case IPV6CTL_MAXFRAGPACKETS:
>  	case IPV6CTL_LOG_INTERVAL:
>  	case IPV6CTL_HDRNESTLIMIT:
> +	case IPV6CTL_DAD_COUNT:
>  		return (sysctl_bounded_arr(
>  		    ipv6ctl_vars_unlocked, nitems(ipv6ctl_vars_unlocked),
>  		    name, namelen, oldp, oldlenp, newp, newlen));
> Index: sys/netinet6/nd6_nbr.c
> ===================================================================
> RCS file: /cvs/src/sys/netinet6/nd6_nbr.c,v
> retrieving revision 1.161
> diff -u -p -r1.161 nd6_nbr.c
> --- sys/netinet6/nd6_nbr.c	8 Jul 2025 00:47:41 -0000	1.161
> +++ sys/netinet6/nd6_nbr.c	23 Jul 2025 21:35:35 -0000
> @@ -1021,6 +1021,7 @@ nd6_dad_start(struct ifaddr *ifa)
>  	struct in6_ifaddr *ia6 = ifatoia6(ifa);
>  	struct dadq *dp;
>  	char addr[INET6_ADDRSTRLEN];
> +	int ip6_dad_count_local = atomic_load_int(&ip6_dad_count);
>  
>  	NET_ASSERT_LOCKED();
>  
> @@ -1031,7 +1032,7 @@ nd6_dad_start(struct ifaddr *ifa)
>  	 * - the interface address is anycast
>  	 */
>  	KASSERT(ia6->ia6_flags & IN6_IFF_TENTATIVE);
> -	if ((ia6->ia6_flags & IN6_IFF_ANYCAST) || (!ip6_dad_count)) {
> +	if ((ia6->ia6_flags & IN6_IFF_ANYCAST) || ip6_dad_count_local == 0) {
>  		ia6->ia6_flags &= ~IN6_IFF_TENTATIVE;
>  
>  		rtm_addr(RTM_CHGADDRATTR, ifa);
> @@ -1062,7 +1063,7 @@ nd6_dad_start(struct ifaddr *ifa)
>  	 * (re)initialization.
>  	 */
>  	dp->dad_ifa = ifaref(ifa);
> -	dp->dad_count = ip6_dad_count;
> +	dp->dad_count = ip6_dad_count_local;
>  	dp->dad_ns_icount = dp->dad_na_icount = 0;
>  	dp->dad_ns_ocount = dp->dad_ns_tcount = 0;
>  	nd6_dad_ns_output(dp, ifa);