ipv6: fix a potential deadlock in do_ipv6_setsockopt()

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 <sploving1@gmail.com>
Tested-by: Baozeng Ding <sploving1@gmail.com>
Cc: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Reviewed-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 14 insertions, 6 deletions

diff --git a/net/ipv6/ipv6_sockglue.c b/net/ipv6/ipv6_sockglue.c
index 5330262ab673..636ec56f5f50 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:
@@ -198,7 +199,7 @@ static int do_ipv6_setsockopt(struct sock *sk, int level, int optname,
                         }
 
                         fl6_free_socklist(sk);
-                        ipv6_sock_mc_close(sk);
+                        __ipv6_sock_mc_close(sk);
 
                         /*
                          * Sock is moving from IPv6 to IPv4 (sk_prot), so
diff --git a/net/ipv6/mcast.c b/net/ipv6/mcast.c
index 75c1fc54f188..14a3903f1c82 100644
--- a/net/ipv6/mcast.c
+++ b/net/ipv6/mcast.c
@@ -276,16 +276,14 @@ static struct inet6_dev *ip6_mc_find_dev_rcu(struct net *net,
         return idev;
 }
 
-void ipv6_sock_mc_close(struct sock *sk)
+void __ipv6_sock_mc_close(struct sock *sk)
 {
         struct ipv6_pinfo *np = inet6_sk(sk);
         struct ipv6_mc_socklist *mc_lst;
         struct net *net = sock_net(sk);
 
-        if (!rcu_access_pointer(np->ipv6_mc_list))
-                return;
+        ASSERT_RTNL();
 
-        rtnl_lock();
         while ((mc_lst = rtnl_dereference(np->ipv6_mc_list)) != NULL) {
                 struct net_device *dev;
 
@@ -303,8 +301,17 @@ void ipv6_sock_mc_close(struct sock *sk)
 
                 atomic_sub(sizeof(*mc_lst), &sk->sk_omem_alloc);
                 kfree_rcu(mc_lst, rcu);
-
         }
+}
+
+void ipv6_sock_mc_close(struct sock *sk)
+{
+        struct ipv6_pinfo *np = inet6_sk(sk);
+
+        if (!rcu_access_pointer(np->ipv6_mc_list))
+                return;
+        rtnl_lock();
+        __ipv6_sock_mc_close(sk);
         rtnl_unlock();
 }