netns: enable to inherit devconf from current netns

The goal is to be able to inherit the initial devconf parameters from the
current netns, ie the netns where this new netns has been created.

This is useful in a containers environment where /proc/sys is read only.
For example, if a pod is created with specifics devconf parameters and has
the capability to create netns, the user expects to get the same parameters
than his 'init_net', which is not the real init_net in this case.

Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/addrconf.c

@@ -6991,9 +6991,26 @@ static int __net_init addrconf_init_net(struct net *net)
 		goto err_alloc_dflt;
 
 	if (IS_ENABLED(CONFIG_SYSCTL) &&
-	    sysctl_devconf_inherit_init_net == 1 && !net_eq(net, &init_net)) {
-		memcpy(all, init_net.ipv6.devconf_all, sizeof(ipv6_devconf));
-		memcpy(dflt, init_net.ipv6.devconf_dflt, sizeof(ipv6_devconf_dflt));
+	    !net_eq(net, &init_net)) {
+		switch (sysctl_devconf_inherit_init_net) {
+		case 1:  /* copy from init_net */
+			memcpy(all, init_net.ipv6.devconf_all,
+			       sizeof(ipv6_devconf));
+			memcpy(dflt, init_net.ipv6.devconf_dflt,
+			       sizeof(ipv6_devconf_dflt));
+			break;
+		case 3: /* copy from the current netns */
+			memcpy(all, current->nsproxy->net_ns->ipv6.devconf_all,
+			       sizeof(ipv6_devconf));
+			memcpy(dflt,
+			       current->nsproxy->net_ns->ipv6.devconf_dflt,
+			       sizeof(ipv6_devconf_dflt));
+			break;
+		case 0:
+		case 2:
+			/* use compiled values */
+			break;
+		}
 	}
 
 	/* these will be inherited by all namespaces */