netdev - Re: [PATCH net] tcp: be more careful in tcp

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Date:   Sun, 21 Jul 2019 20:42:10 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     edumazet@...gle.com
Cc:     netdev@...r.kernel.org, eric.dumazet@...il.com, aprout@...mit.edu,
        jonathan.lemon@...il.com, mkubecek@...e.cz, ncardwell@...gle.com,
        ycheng@...gle.com, cpaasch@...le.com, jtl@...flix.com
Subject: Re: [PATCH net] tcp: be more careful in tcp_fragment()

From: Eric Dumazet <edumazet@...gle.com>
Date: Fri, 19 Jul 2019 11:52:33 -0700

> Some applications set tiny SO_SNDBUF values and expect
> TCP to just work. Recent patches to address CVE-2019-11478
> broke them in case of losses, since retransmits might
> be prevented.
> 
> We should allow these flows to make progress.
> 
> This patch allows the first and last skb in retransmit queue
> to be split even if memory limits are hit.
> 
> It also adds the some room due to the fact that tcp_sendmsg()
> and tcp_sendpage() might overshoot sk_wmem_queued by about one full
> TSO skb (64KB size). Note this allowance was already present
> in stable backports for kernels < 4.15
> 
> Note for < 4.15 backports :
>  tcp_rtx_queue_tail() will probably look like :
> 
> static inline struct sk_buff *tcp_rtx_queue_tail(const struct sock *sk)
> {
> 	struct sk_buff *skb = tcp_send_head(sk);
> 
> 	return skb ? tcp_write_queue_prev(sk, skb) : tcp_write_queue_tail(sk);
> }
> 
> Fixes: f070ef2ac667 ("tcp: tcp_fragment() should apply sane memory limits")
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: Andrew Prout <aprout@...mit.edu>
> Tested-by: Andrew Prout <aprout@...mit.edu>
> Tested-by: Jonathan Lemon <jonathan.lemon@...il.com>
> Tested-by: Michal Kubecek <mkubecek@...e.cz>
> Acked-by: Neal Cardwell <ncardwell@...gle.com>
> Acked-by: Yuchung Cheng <ycheng@...gle.com>
> Acked-by: Christoph Paasch <cpaasch@...le.com>
> Cc: Jonathan Looney <jtl@...flix.com>

Applied and queued up for -stable.