ipv6: do not abuse GFP_ATOMIC in inet6_netconf_notify_devconf()

BugLink: https://bugs.launchpad.net/bugs/1878232

commit 927265bc upstream.

All inet6_netconf_notify_devconf() callers are in process context,
so we can use GFP_KERNEL allocations if we take care of not holding
a rwlock while not needed in ip6mr (we hold RTNL there)

Fixes: d67b8c61 ("netconf: advertise mc_forwarding status")
Fixes: f3a1bfb1 ("rtnl/ipv6: use netconf msg to advertise forwarding status")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Acked-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ian May <ian.may@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

net/ipv6/addrconf.c

@@ -540,7 +540,7 @@ void inet6_netconf_notify_devconf(struct net *net, int type, int ifindex,
 	struct sk_buff *skb;
 	int err = -ENOBUFS;
 
-	skb = nlmsg_new(inet6_netconf_msgsize_devconf(type), GFP_ATOMIC);
+	skb = nlmsg_new(inet6_netconf_msgsize_devconf(type), GFP_KERNEL);
 	if (!skb)
 		goto errout;
 
@@ -552,7 +552,7 @@ void inet6_netconf_notify_devconf(struct net *net, int type, int ifindex,
 		kfree_skb(skb);
 		goto errout;
 	}
-	rtnl_notify(skb, net, 0, RTNLGRP_IPV6_NETCONF, NULL, GFP_ATOMIC);
+	rtnl_notify(skb, net, 0, RTNLGRP_IPV6_NETCONF, NULL, GFP_KERNEL);
 	return;
 errout:
 	rtnl_set_sk_err(net, RTNLGRP_IPV6_NETCONF, err);

net/ipv6/ip6mr.c

@@ -1594,14 +1594,15 @@ static int ip6mr_sk_init(struct mr6_table *mrt, struct sock *sk)
 	if (likely(mrt->mroute6_sk == NULL)) {
 		mrt->mroute6_sk = sk;
 		net->ipv6.devconf_all->mc_forwarding++;
-		inet6_netconf_notify_devconf(net, NETCONFA_MC_FORWARDING,
-					     NETCONFA_IFINDEX_ALL,
-					     net->ipv6.devconf_all);
-	}
-	else
+	} else {
 		err = -EADDRINUSE;
+	}
 	write_unlock_bh(&mrt_lock);
 
+	if (!err)
+		inet6_netconf_notify_devconf(net, NETCONFA_MC_FORWARDING,
+					     NETCONFA_IFINDEX_ALL,
+					     net->ipv6.devconf_all);
 	rtnl_unlock();
 
 	return err;
@@ -1619,11 +1620,11 @@ int ip6mr_sk_done(struct sock *sk)
 			write_lock_bh(&mrt_lock);
 			mrt->mroute6_sk = NULL;
 			net->ipv6.devconf_all->mc_forwarding--;
+			write_unlock_bh(&mrt_lock);
 			inet6_netconf_notify_devconf(net,
 						     NETCONFA_MC_FORWARDING,
 						     NETCONFA_IFINDEX_ALL,
 						     net->ipv6.devconf_all);
-			write_unlock_bh(&mrt_lock);
 
 			mroute_clean_tables(mrt, false);
 			err = 0;