[PATCH 4.4 156/266] ipv6: fix a potential deadlock in do_ipv6_setsockopt()

[Greg Kroah-Hartman]

From: WANG Cong <xiyou.wangc...@gmail.com>

commit 8651be8f14a12d24f203f283601d9b0418c389ff upstream.

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>
Reviewed-by: Marcelo Ricardo Leitner <marcelo.leit...@gmail.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
Cc: Zubin Mithra <z...@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 include/net/addrconf.h   |    1 +
 net/ipv6/ipv6_sockglue.c |    3 ++-
 net/ipv6/mcast.c         |   17 ++++++++++++-----
 3 files changed, 15 insertions(+), 6 deletions(-)

--- a/include/net/addrconf.h
+++ b/include/net/addrconf.h
@@ -162,6 +162,7 @@ int ipv6_sock_mc_join(struct sock *sk, i
                      const struct in6_addr *addr);
 int ipv6_sock_mc_drop(struct sock *sk, int ifindex,
                      const struct in6_addr *addr);
+void __ipv6_sock_mc_close(struct sock *sk);
 void ipv6_sock_mc_close(struct sock *sk);
 bool inet6_mc_check(struct sock *sk, const struct in6_addr *mc_addr,
                    const struct in6_addr *src_addr);
--- a/net/ipv6/ipv6_sockglue.c
+++ b/net/ipv6/ipv6_sockglue.c
@@ -121,6 +121,7 @@ struct ipv6_txoptions *ipv6_update_optio
 static bool setsockopt_needs_rtnl(int optname)
 {
        switch (optname) {
+       case IPV6_ADDRFORM:
        case IPV6_ADD_MEMBERSHIP:
        case IPV6_DROP_MEMBERSHIP:
        case IPV6_JOIN_ANYCAST:
@@ -199,7 +200,7 @@ static int do_ipv6_setsockopt(struct soc
                        }
 
                        fl6_free_socklist(sk);
-                       ipv6_sock_mc_close(sk);
+                       __ipv6_sock_mc_close(sk);
 
                        /*
                         * Sock is moving from IPv6 to IPv4 (sk_prot), so
--- a/net/ipv6/mcast.c
+++ b/net/ipv6/mcast.c
@@ -276,16 +276,14 @@ static struct inet6_dev *ip6_mc_find_dev
        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();
 }