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

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Message-ID: <1473957329.22679.52.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Thu, 15 Sep 2016 09:35:29 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     David Miller <davem@...emloft.net>, netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net] tcp: fix overflow in __tcp_retransmit_skb()

On Thu, 2016-09-15 at 15:52 +0000, David Laight wrote:
> 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;

Well, I find the existing code more readable, but this is just an
opinion.

Thanks.