linux-kernel - Re: [PATCH bpf-next v3 1/3] bpf, sockmap: avoid using sk

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Message-ID: <Z9tb+Y+w/gcqSnCo@pop-os.localdomain>
Date: Wed, 19 Mar 2025 17:06:17 -0700
From: Cong Wang <xiyou.wangcong@...il.com>
To: Jiayuan Chen <jiayuan.chen@...ux.dev>
Cc: john.fastabend@...il.com, jakub@...udflare.com, davem@...emloft.net,
	edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
	horms@...nel.org, andrii@...nel.org, eddyz87@...il.com,
	mykolal@...com, ast@...nel.org, daniel@...earbox.net,
	martin.lau@...ux.dev, song@...nel.org, yonghong.song@...ux.dev,
	kpsingh@...nel.org, sdf@...ichev.me, haoluo@...gle.com,
	jolsa@...nel.org, shuah@...nel.org, mhal@...x.co,
	sgarzare@...hat.com, netdev@...r.kernel.org, bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH bpf-next v3 1/3] bpf, sockmap: avoid using sk_socket
 after free when sending

On Wed, Mar 19, 2025 at 11:36:13PM +0000, Jiayuan Chen wrote:
> 2025/3/20 07:02, "Cong Wang" <xiyou.wangcong@...il.com> wrote:
> 
> > 
> > On Mon, Mar 17, 2025 at 05:22:54PM +0800, Jiayuan Chen wrote:
> > 
> > > 
> > > The sk->sk_socket is not locked or referenced, and during the call to
> > > 
> > 
> > Hm? We should have a reference in socket map, whether directly or
> > 
> > indirectly, right? When we add a socket to a socket map, we do call
> > 
> > sock_map_psock_get_checked() to obtain a reference.
> > 
> 
> Yes, but we remove psock from sockmap when sock_map_close() was called
> '''
> sock_map_close
> 	lock_sock(sk);
> 	rcu_read_lock();
> 	psock = sk_psock(sk);
>         // here we remove psock and the reference of psock become 0
> 	sock_map_remove_links(sk, psock)

sk_psock_drop() also calls cancel_delayed_work_sync(&psock->work),
althrough in yet another work. Is this also a contribution to this bug?

>         psock = sk_psock_get(sk);
>         if (unlikely(!psock))
>             goto no_psock;     <=== jmp to no_psock
>         rcu_read_unlock();
>         release_sock(sk);
>         cancel_delayed_work_sync(&psock->work); <== no chance to run cancel
> '''
> 

I have to say sock_map_close() becomes harder and harder to understand
now. And I am feeling we may have more bugs since we have two flying
work's here: psock->rwork and psock->work.

Thanks.