cgroup: duplicate cgroup reference when cloning sockets

When a socket is cloned, the associated sock_cgroup_data is duplicated
but not its reference on the cgroup.  As a result, the cgroup reference
count will underflow when both sockets are destroyed later on.

Fixes: bd1060a1d671 ("sock, cgroup: add sock->sk_cgroup")
Link: http://lkml.kernel.org/r/20160914194846.11153-2-hannes@cmpxchg.org
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
Cc: <stable@vger.kernel.org>	[4.5+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 10 insertions, 1 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index d1c51b7f5221..5e8dab5bf9ad 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -6270,6 +6270,12 @@ void cgroup_sk_alloc(struct sock_cgroup_data *skcd)
         if (cgroup_sk_alloc_disabled)
                 return;
 
+        /* Socket clone path */
+        if (skcd->val) {
+                cgroup_get(sock_cgroup_ptr(skcd));
+                return;
+        }
+
         rcu_read_lock();
 
         while (true) {
diff --git a/net/core/sock.c b/net/core/sock.c
index 25dab8b60223..fd7b41edf1ce 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1362,7 +1362,6 @@ static struct sock *sk_prot_alloc(struct proto *prot, gfp_t priority,
                 if (!try_module_get(prot->owner))
                         goto out_free_sec;
                 sk_tx_queue_clear(sk);
-                cgroup_sk_alloc(&sk->sk_cgrp_data);
         }
 
         return sk;
@@ -1422,6 +1421,7 @@ struct sock *sk_alloc(struct net *net, int family, gfp_t priority,
                 sock_net_set(sk, net);
                 atomic_set(&sk->sk_wmem_alloc, 1);
 
+                cgroup_sk_alloc(&sk->sk_cgrp_data);
                 sock_update_classid(&sk->sk_cgrp_data);
                 sock_update_netprioidx(&sk->sk_cgrp_data);
         }
@@ -1566,6 +1566,9 @@ struct sock *sk_clone_lock(const struct sock *sk, const gfp_t priority)
                 newsk->sk_priority = 0;
                 newsk->sk_incoming_cpu = raw_smp_processor_id();
                 atomic64_set(&newsk->sk_cookie, 0);
+
+                cgroup_sk_alloc(&newsk->sk_cgrp_data);
+
                 /*
                  * Before updating sk_refcnt, we must commit prior changes to memory
                  * (Documentation/RCU/rculist_nulls.txt for details)