From: Vitaliy Makkoveev <mvs@openbsd.org>
Subject: Unlock IPV6CTL_DAD_COUNT case of ip6_sysctl()
To: Alexander Bluhm <bluhm@openbsd.org>, tech@openbsd.org
Date: Thu, 24 Jul 2025 00:41:18 +0300

`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.

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);