[Patch net] ipv6: fix a potential deadlock in do_ipv6_setsockopt()

[Cong Wang]

Baozeng reported this deadlock case:

       CPU0                    CPU1
       ----                    ----
  lock([  165.136033] sk_lock-AF_INET6);
                               lock([  165.136033] rtnl_mutex);
                               lock([  165.136033] sk_lock-AF_INET6);
  lock([  165.136033] rtnl_mutex);

Similar to commit 87e9f0315952
("ipv4: fix a potential deadlock in mcast getsockopt() path")
this is due to we still have a case, ipv6_sock_mc_close(),
where we acquire sk_lock before rtnl_lock. Close this deadlock
with the similar solution, that is always acquire rtnl lock first.

Fixes: baf606d9c9b1 ("ipv4,ipv6: grab rtnl before locking the socket")
Reported-by: Baozeng Ding <splovi...@gmail.com>
Tested-by: Baozeng Ding <splovi...@gmail.com>
Cc: Marcelo Ricardo Leitner <marcelo.leit...@gmail.com>
Signed-off-by: Cong Wang <xiyou.wangc...@gmail.com>
---
 net/ipv6/af_inet6.c      | 2 ++
 net/ipv6/ipv6_sockglue.c | 1 +
 net/ipv6/mcast.c         | 4 ++--
 3 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/net/ipv6/af_inet6.c b/net/ipv6/af_inet6.c
index 46ad699..b8c8d20 100644
--- a/net/ipv6/af_inet6.c
+++ b/net/ipv6/af_inet6.c
@@ -414,7 +414,9 @@ int inet6_release(struct socket *sock)
                return -EINVAL;
 
        /* Free mc lists */
+       rtnl_lock();
        ipv6_sock_mc_close(sk);
+       rtnl_unlock();
 
        /* Free ac lists */
        ipv6_sock_ac_close(sk);
diff --git a/net/ipv6/ipv6_sockglue.c b/net/ipv6/ipv6_sockglue.c
index 5330262..1e4bcce 100644
--- a/net/ipv6/ipv6_sockglue.c
+++ b/net/ipv6/ipv6_sockglue.c
@@ -120,6 +120,7 @@ struct ipv6_txoptions *ipv6_update_options(struct sock *sk,
 static bool setsockopt_needs_rtnl(int optname)
 {
        switch (optname) {
+       case IPV6_ADDRFORM:
        case IPV6_ADD_MEMBERSHIP:
        case IPV6_DROP_MEMBERSHIP:
        case IPV6_JOIN_ANYCAST:
diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c
index 75c1fc5..41badfd 100644
--- a/net/ipv6/mcast.c
+++ b/net/ipv6/mcast.c
@@ -282,10 +282,11 @@ void ipv6_sock_mc_close(struct sock *sk)
        struct ipv6_mc_socklist *mc_lst;
        struct net *net = sock_net(sk);
 
+       ASSERT_RTNL();
+
        if (!rcu_access_pointer(np->ipv6_mc_list))
                return;
 
-       rtnl_lock();
        while ((mc_lst = rtnl_dereference(np->ipv6_mc_list)) != NULL) {
                struct net_device *dev;
 
@@ -305,7 +306,6 @@ void ipv6_sock_mc_close(struct sock *sk)
                kfree_rcu(mc_lst, rcu);
 
        }
-       rtnl_unlock();
 }
 
 int ip6_mc_source(int add, int omode, struct sock *sk,
-- 
2.1.0