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Date:   Wed, 21 Jul 2021 18:36:23 +0200
From:   Jakub Sitnicki <jakub@...udflare.com>
To:     John Fastabend <john.fastabend@...il.com>
Cc:     daniel@...earbox.net, xiyou.wangcong@...il.com,
        alexei.starovoitov@...il.com, bpf@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH bpf 3/3] bpf, sockmap: fix memleak on ingress msg enqueue

On Mon, Jul 19, 2021 at 11:48 PM CEST, John Fastabend wrote:
> If backlog handler is running during a tear down operation we may enqueue
> data on the ingress msg queue while tear down is trying to free it.
>
>  sk_psock_backlog()
>    sk_psock_handle_skb()
>      skb_psock_skb_ingress()
>        sk_psock_skb_ingress_enqueue()
>          sk_psock_queue_msg(psock,msg)
>                                            spin_lock(ingress_lock)
>                                             sk_psock_zap_ingress()
>                                              _sk_psock_purge_ingerss_msg()
>                                               _sk_psock_purge_ingress_msg()
>                                             -- free ingress_msg list --
>                                            spin_unlock(ingress_lock)
>            spin_lock(ingress_lock)
>            list_add_tail(msg,ingress_msg) <- entry on list with no on
>                                              left to free it.
>            spin_unlock(ingress_lock)
>
> To fix we only enqueue from backlog if the ENABLED bit is set. The tear
> down logic clears the bit with ingress_lock set so we wont enqueue the
> msg in the last step.
>
> Fixes: 799aa7f98d53 ("skmsg: Avoid lock_sock() in sk_psock_backlog()")
> Signed-off-by: John Fastabend <john.fastabend@...il.com>
> ---
>  include/linux/skmsg.h | 54 ++++++++++++++++++++++++++++---------------
>  net/core/skmsg.c      |  6 -----
>  2 files changed, 35 insertions(+), 25 deletions(-)
>
> diff --git a/include/linux/skmsg.h b/include/linux/skmsg.h
> index 96f319099744..883638888f93 100644
> --- a/include/linux/skmsg.h
> +++ b/include/linux/skmsg.h
> @@ -285,11 +285,45 @@ static inline struct sk_psock *sk_psock(const struct sock *sk)
>  	return rcu_dereference_sk_user_data(sk);
>  }
>  
> +static inline void sk_psock_set_state(struct sk_psock *psock,
> +				      enum sk_psock_state_bits bit)
> +{
> +	set_bit(bit, &psock->state);
> +}
> +
> +static inline void sk_psock_clear_state(struct sk_psock *psock,
> +					enum sk_psock_state_bits bit)
> +{
> +	clear_bit(bit, &psock->state);
> +}
> +
> +static inline bool sk_psock_test_state(const struct sk_psock *psock,
> +				       enum sk_psock_state_bits bit)
> +{
> +	return test_bit(bit, &psock->state);
> +}
> +
> +static void sock_drop(struct sock *sk, struct sk_buff *skb)
> +{
> +	sk_drops_add(sk, skb);
> +	kfree_skb(skb);
> +}
> +
> +static inline void drop_sk_msg(struct sk_psock *psock, struct sk_msg *msg)
> +{
> +	if (msg->skb)
> +		sock_drop(psock->sk, msg->skb);
> +	kfree(msg);
> +}
> +
>  static inline void sk_psock_queue_msg(struct sk_psock *psock,
>  				      struct sk_msg *msg)
>  {
>  	spin_lock_bh(&psock->ingress_lock);
> -	list_add_tail(&msg->list, &psock->ingress_msg);
> +        if (sk_psock_test_state(psock, SK_PSOCK_TX_ENABLED))


Whitespace issue ^. Otherwise LGTM.

> +		list_add_tail(&msg->list, &psock->ingress_msg);
> +	else
> +		drop_sk_msg(psock, msg);
>  	spin_unlock_bh(&psock->ingress_lock);
>  }
>  

[...]

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