linux-kernel - [PATCH 4.7 18/69] cgroup: duplicate cgroup reference when cloning sockets

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Date:   Wed, 28 Sep 2016 11:05:00 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Johannes Weiner <hannes@...xchg.org>,
        Tejun Heo <tj@...nel.org>, Michal Hocko <mhocko@...e.cz>,
        Vladimir Davydov <vdavydov@...tuozzo.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4.7 18/69] cgroup: duplicate cgroup reference when cloning sockets

4.7-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Johannes Weiner <jweiner@...com>

commit d979a39d7242e0601bf9b60e89628fb8ac577179 upstream.

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@...xchg.org>
Acked-by: Tejun Heo <tj@...nel.org>
Cc: Michal Hocko <mhocko@...e.cz>
Cc: Vladimir Davydov <vdavydov@...tuozzo.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 kernel/cgroup.c |    6 ++++++
 net/core/sock.c |    5 ++++-
 2 files changed, 10 insertions(+), 1 deletion(-)

--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -6240,6 +6240,12 @@ void cgroup_sk_alloc(struct sock_cgroup_
 	if (cgroup_sk_alloc_disabled)
 		return;
 
+	/* Socket clone path */
+	if (skcd->val) {
+		cgroup_get(sock_cgroup_ptr(skcd));
+		return;
+	}
+
 	rcu_read_lock();
 
 	while (true) {
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1362,7 +1362,6 @@ static struct sock *sk_prot_alloc(struct
 		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, i
 		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
 		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)