[PATCH 5.15.y 1/4] ip6mr: ip6mr_sk_done() can exit early in common cases

[Sasha Levin <sashal@kernel.org>]

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit f2f2325ec79970807012dfc9e716cdbb02d9b574 ]

In many cases, ip6mr_sk_done() is called while no ipmr socket
has been registered.

This removes 4 rtnl acquisitions per netns dismantle,
with following callers:

igmp6_net_exit(), tcpv6_net_exit(), ndisc_net_exit()

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Stable-dep-of: 6ace56ed7b13 ("ipv6: remove ifaddr from hash during ifdown list cleanup")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 net/ipv6/ip6mr.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
index a793dcd24813e..0e2c566ec04b8 100644
--- a/net/ipv6/ip6mr.c
+++ b/net/ipv6/ip6mr.c
@@ -1581,6 +1581,9 @@ int ip6mr_sk_done(struct sock *sk)
 	    inet_sk(sk)->inet_num != IPPROTO_ICMPV6)
 		return err;
 
+	if (!atomic_read(&net->ipv6.devconf_all->mc_forwarding))
+		return err;
+
 	rtnl_lock();
 	ip6mr_for_each_table(mrt, net) {
 		if (sk == rtnl_dereference(mrt->mroute_sk)) {
-- 
2.53.0