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

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Message-ID: <48068a86ea99dffe1e7849fb544eac1746364afb@linux.dev>
Date: Wed, 19 Mar 2025 23:36:13 +0000
From: "Jiayuan Chen" <jiayuan.chen@...ux.dev>
To: "Cong Wang" <xiyou.wangcong@...il.com>
Cc: john.fastabend@...il.com, jakub@...udflare.com, davem@...emloft.net,
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Subject: Re: [PATCH bpf-next v3 1/3] bpf, sockmap: avoid using sk_socket
 after free when sending

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)
        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
'''

So I think we should hold the psock when backlog running

Thanks,