netdev - Re: Fw: Linux tcp_xmit_retransmit_queue use after free on 4.8-rc1 / master]

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Message-ID: <1471379491.4943.15.camel@edumazet-glaptop3.roam.corp.google.com>
Date:	Tue, 16 Aug 2016 13:31:31 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Cong Wang <xiyou.wangcong@...il.com>
Cc:	Greg KH <gregkh@...uxfoundation.org>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	Marco Grassi <marco.gra@...il.com>,
	Yuchung Cheng <ycheng@...gle.com>,
	Neal Cardwell <ncardwell@...gle.com>
Subject: Re: Fw: Linux tcp_xmit_retransmit_queue use after free on 4.8-rc1 /
 master]

On Tue, 2016-08-16 at 13:27 -0700, Eric Dumazet wrote:

> 
> Look at skb_entail() : It calls tcp_add_write_queue_tail()
> 
> And tcp_add_write_queue_tail() looks like :
> 
> 
> static inline void tcp_add_write_queue_tail(struct sock *sk, struct sk_buff *skb)
> {
>         __tcp_add_write_queue_tail(sk, skb);
> 
>         /* Queue it, remembering where we must start sending. */
>         if (sk->sk_send_head == NULL) {
>                 sk->sk_send_head = skb;
> 
>                 if (tcp_sk(sk)->highest_sack == NULL)
>                         tcp_sk(sk)->highest_sack = skb;
>         }
> }
> 
> 
> So we definitely need to undo what tcp_add_write_queue_tail() did.

So the bug was probably added in 2.6.25 

commit 6859d49475d4f32abe640372117e4b687906e6b6
Author: Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
Date:   Sun Dec 2 00:48:06 2007 +0200

    [TCP]: Abstract tp->highest_sack accessing & point to next skb
    
    Pointing to the next skb is necessary to avoid referencing
    already SACKed skbs which will soon be on a separate list.
    
    Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
    Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>
    Signed-off-by: David S. Miller <davem@...emloft.net>