netdev - RE: [PATCH net] tcp: fix overflow in __tcp_retransmit

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Date:   Thu, 15 Sep 2016 15:52:06 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Eric Dumazet' <eric.dumazet@...il.com>,
        David Miller <davem@...emloft.net>
CC:     netdev <netdev@...r.kernel.org>
Subject: RE: [PATCH net] tcp: fix overflow in __tcp_retransmit_skb()

From: Eric Dumazet
> Sent: 15 September 2016 16:13
> If a TCP socket gets a large write queue, an overflow can happen
> in a test in __tcp_retransmit_skb() preventing all retransmits.
...
>  	if (atomic_read(&sk->sk_wmem_alloc) >
> -	    min(sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2), sk->sk_sndbuf))
> +	    min_t(u32, sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2),
> +		  sk->sk_sndbuf))
>  		return -EAGAIN;

Might it also be better to split that test to (say):

	u32 wmem_alloc = atomic_read(&sk->sk_wmem_alloc);
	if (unlikely((wmem_alloc > sk->sk_sndbuf))
		return -EAGAIN;
	if (unlikely(wmem_alloc > sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2)))
		return -EAGAIN;

It might even be worth splitting the second test as:

	if (unlikely(wmem_alloc > sk->sk_wmem_queued)
	    && wmem_alloc > sk->sk_wmem_queued + (sk->sk_wmem_queued >> 2))
		return -EAGAIN;

	David