Re: net/ipv6: potential deadlock in do_ipv6_setsockopt

[Cong Wang]

On Sun, Oct 16, 2016 at 6:34 AM, Baozeng Ding <splovi...@gmail.com> wrote:
>  Possible unsafe locking scenario:
>
>        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
> );
>
>  *** DEADLOCK ***

This is caused by the conditional rtnl locking in do_ipv6_setsockopt().
It looks like we miss the case of IPV6_ADDRFORM.

Please try the attached patch.

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,