netdev - Re: [PATCH bpf-next 1/4] bpf, sockmap: Fix memleak in sk_psock_queue

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Date:   Wed, 2 Mar 2022 16:31:12 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     wangyufen <wangyufen@...wei.com>
Cc:     john.fastabend@...il.com, daniel@...earbox.net,
        jakub@...udflare.com, lmb@...udflare.com, davem@...emloft.net,
        bpf@...r.kernel.org, edumazet@...gle.com, yoshfuji@...ux-ipv6.org,
        dsahern@...nel.org, kuba@...nel.org, ast@...nel.org,
        andrii@...nel.org, kafai@...com, songliubraving@...com, yhs@...com,
        kpsingh@...nel.org, netdev@...r.kernel.org
Subject: Re: [PATCH bpf-next 1/4] bpf, sockmap: Fix memleak in
 sk_psock_queue_msg

On Tue, Mar 01, 2022 at 09:49:12AM +0800, wangyufen wrote:
> 
> 在 2022/2/28 3:21, Cong Wang 写道:
> > On Fri, Feb 25, 2022 at 09:49:26AM +0800, Wang Yufen wrote:
> > > If tcp_bpf_sendmsg is running during a tear down operation we may enqueue
> > > data on the ingress msg queue while tear down is trying to free it.
> > > 
> > >   sk1 (redirect sk2)                         sk2
> > >   -------------------                      ---------------
> > > tcp_bpf_sendmsg()
> > >   tcp_bpf_send_verdict()
> > >    tcp_bpf_sendmsg_redir()
> > >     bpf_tcp_ingress()
> > >                                            sock_map_close()
> > >                                             lock_sock()
> > >      lock_sock() ... blocking
> > >                                             sk_psock_stop
> > >                                              sk_psock_clear_state(psock, SK_PSOCK_TX_ENABLED);
> > >                                             release_sock(sk);
> > >      lock_sock()	
> > >      sk_mem_charge()
> > >      get_page()
> > >      sk_psock_queue_msg()
> > >       sk_psock_test_state(psock, SK_PSOCK_TX_ENABLED);
> > >        drop_sk_msg()
> > >      release_sock()
> > > 
> > > While drop_sk_msg(), the msg has charged memory form sk by sk_mem_charge
> > > and has sg pages need to put. To fix we use sk_msg_free() and then kfee()
> > > msg.
> > > 
> > What about the other code path? That is, sk_psock_skb_ingress_enqueue().
> > I don't see skmsg is charged there.
> 
> sk_psock_skb_ingress_self() | sk_psock_skb_ingress()
>    skb_set_owner_r()
>       sk_mem_charge()
>    sk_psock_skb_ingress_enqueue()
> 
> The other code path skmsg is charged by skb_set_owner_r()->sk_mem_charge()
> 

skb_set_owner_r() charges skb, I was asking skmsg. ;) In
sk_psock_skb_ingress_enqueue(), the skmsg was initialized but not
actually charged, hence I was asking... From a second look, it seems
sk_mem_uncharge() is not called for sk_psock_skb_ingress_enqueue() where
msg->skb is clearly not NULL.

Also, you introduce an unnecessary sk_msg_init() from __sk_msg_free(),
because you call kfree(msg) after it.

Thanks.