ipv6: fix net.ipv6.conf.all interface DAD handlers

Currently, writing into
net.ipv6.conf.all.{accept_dad,use_optimistic,optimistic_dad} has no effect.
Fix handling of these flags by:

- using the maximum of global and per-interface values for the
  accept_dad flag. That is, if at least one of the two values is
  non-zero, enable DAD on the interface. If at least one value is
  set to 2, enable DAD and disable IPv6 operation on the interface if
  MAC-based link-local address was found

- using the logical OR of global and per-interface values for the
  optimistic_dad flag. If at least one of them is set to one, optimistic
  duplicate address detection (RFC 4429) is enabled on the interface

- using the logical OR of global and per-interface values for the
  use_optimistic flag. If at least one of them is set to one,
  optimistic addresses won't be marked as deprecated during source address
  selection on the interface.

While at it, as we're modifying the prototype for ipv6_use_optimistic_addr(),
drop inline, and let the compiler decide.

Fixes: 7fd2561e ("net: ipv6: Add a sysctl to make optimistic addresses useful candidates")
Signed-off-by: Matteo Croce <mcroce@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/ip-sysctl.txt

@@ -1680,6 +1680,9 @@ accept_dad - INTEGER
 	2: Enable DAD, and disable IPv6 operation if MAC-based duplicate
 	   link-local address has been found.
 
+	DAD operation and mode on a given interface will be selected according
+	to the maximum value of conf/{all,interface}/accept_dad.
+
 force_tllao - BOOLEAN
 	Enable sending the target link-layer address option even when
 	responding to a unicast neighbor solicitation.
@@ -1730,6 +1733,10 @@ optimistic_dad - BOOLEAN
 	0: disabled (default)
 	1: enabled
 
+	Optimistic Duplicate Address Detection for the interface will be enabled
+	if at least one of conf/{all,interface}/optimistic_dad is set to 1,
+	it will be disabled otherwise.
+
 use_optimistic - BOOLEAN
 	If enabled, do not classify optimistic addresses as deprecated during
 	source address selection.  Preferred addresses will still be chosen
@@ -1738,6 +1745,9 @@ use_optimistic - BOOLEAN
 	0: disabled (default)
 	1: enabled
 
+	This will be enabled if at least one of
+	conf/{all,interface}/use_optimistic is set to 1, disabled otherwise.
+
 stable_secret - IPv6 address
 	This IPv6 address will be used as a secret to generate IPv6
 	addresses for link-local addresses and autoconfigured

net/ipv6/addrconf.c

@@ -1399,10 +1399,18 @@ static inline int ipv6_saddr_preferred(int type)
 	return 0;
 }
 
-static inline bool ipv6_use_optimistic_addr(struct inet6_dev *idev)
+static bool ipv6_use_optimistic_addr(struct net *net,
+				     struct inet6_dev *idev)
 {
 #ifdef CONFIG_IPV6_OPTIMISTIC_DAD
-	return idev && idev->cnf.optimistic_dad && idev->cnf.use_optimistic;
+	if (!idev)
+		return false;
+	if (!net->ipv6.devconf_all->optimistic_dad && !idev->cnf.optimistic_dad)
+		return false;
+	if (!net->ipv6.devconf_all->use_optimistic && !idev->cnf.use_optimistic)
+		return false;
+
+	return true;
 #else
 	return false;
 #endif
@@ -1472,7 +1480,7 @@ static int ipv6_get_saddr_eval(struct net *net,
 		/* Rule 3: Avoid deprecated and optimistic addresses */
 		u8 avoid = IFA_F_DEPRECATED;
 
-		if (!ipv6_use_optimistic_addr(score->ifa->idev))
+		if (!ipv6_use_optimistic_addr(net, score->ifa->idev))
 			avoid |= IFA_F_OPTIMISTIC;
 		ret = ipv6_saddr_preferred(score->addr_type) ||
 		      !(score->ifa->flags & avoid);
@@ -2460,7 +2468,8 @@ int addrconf_prefix_rcv_add_addr(struct net *net, struct net_device *dev,
 		int max_addresses = in6_dev->cnf.max_addresses;
 
 #ifdef CONFIG_IPV6_OPTIMISTIC_DAD
-		if (in6_dev->cnf.optimistic_dad &&
+		if ((net->ipv6.devconf_all->optimistic_dad ||
+		     in6_dev->cnf.optimistic_dad) &&
 		    !net->ipv6.devconf_all->forwarding && sllao)
 			addr_flags |= IFA_F_OPTIMISTIC;
 #endif
@@ -3051,7 +3060,8 @@ void addrconf_add_linklocal(struct inet6_dev *idev,
 	u32 addr_flags = flags | IFA_F_PERMANENT;
 
 #ifdef CONFIG_IPV6_OPTIMISTIC_DAD
-	if (idev->cnf.optimistic_dad &&
+	if ((dev_net(idev->dev)->ipv6.devconf_all->optimistic_dad ||
+	     idev->cnf.optimistic_dad) &&
 	    !dev_net(idev->dev)->ipv6.devconf_all->forwarding)
 		addr_flags |= IFA_F_OPTIMISTIC;
 #endif
@@ -3810,6 +3820,7 @@ static void addrconf_dad_begin(struct inet6_ifaddr *ifp)
 		goto out;
 
 	if (dev->flags&(IFF_NOARP|IFF_LOOPBACK) ||
+	    dev_net(dev)->ipv6.devconf_all->accept_dad < 1 ||
 	    idev->cnf.accept_dad < 1 ||
 	    !(ifp->flags&IFA_F_TENTATIVE) ||
 	    ifp->flags & IFA_F_NODAD) {
@@ -3841,7 +3852,7 @@ static void addrconf_dad_begin(struct inet6_ifaddr *ifp)
 	 */
 	if (ifp->flags & IFA_F_OPTIMISTIC) {
 		ip6_ins_rt(ifp->rt);
-		if (ipv6_use_optimistic_addr(idev)) {
+		if (ipv6_use_optimistic_addr(dev_net(dev), idev)) {
 			/* Because optimistic nodes can use this address,
 			 * notify listeners. If DAD fails, RTM_DELADDR is sent.
 			 */
@@ -3897,7 +3908,9 @@ static void addrconf_dad_work(struct work_struct *w)
 		action = DAD_ABORT;
 		ifp->state = INET6_IFADDR_STATE_POSTDAD;
 
-		if (idev->cnf.accept_dad > 1 && !idev->cnf.disable_ipv6 &&
+		if ((dev_net(idev->dev)->ipv6.devconf_all->accept_dad > 1 ||
+		     idev->cnf.accept_dad > 1) &&
+		    !idev->cnf.disable_ipv6 &&
 		    !(ifp->flags & IFA_F_STABLE_PRIVACY)) {
 			struct in6_addr addr;