[2/3] cgroup: duplicate cgroup reference when cloning sockets

From: Johannes Weiner <jweiner@fb.com>

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")
Cc: <stable@vger.kernel.org> # 4.5+
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 kernel/cgroup.c | 6 ++++++
 net/core/sock.c | 5 ++++-
 2 files changed, 10 insertions(+), 1 deletion(-)

[Fixup Vladimir's email]

I am not familiar with this code path to give my ack, unfortunatelly.

On Wed 14-09-16 15:48:45, Johannes Weiner wrote:
> From: Johannes Weiner <jweiner@fb.com>
> 
> 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")
> Cc: <stable@vger.kernel.org> # 4.5+
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
> ---
>  kernel/cgroup.c | 6 ++++++
>  net/core/sock.c | 5 ++++-
>  2 files changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index 0c4db7908264..b0d727d26fc7 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -6297,6 +6297,12 @@ 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 51a730485649..038e660ef844 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -1340,7 +1340,6 @@ 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;
> @@ -1400,6 +1399,7 @@ 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);
>  	}
> @@ -1544,6 +1544,9 @@ 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)
> -- 
> 2.9.3

On Wed, Sep 14, 2016 at 03:48:45PM -0400, Johannes Weiner wrote:
> From: Johannes Weiner <jweiner@fb.com>
> 
> 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")
> Cc: <stable@vger.kernel.org> # 4.5+
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

Reviewed-by: Vladimir Davydov <vdavydov.dev@gmail.com>