netdev - Re: [PATCH v2 net-next] tcp: avoid possible arithmetic overflows

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Message-ID: <1411389739.26859.113.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Mon, 22 Sep 2014 05:42:19 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Yuchung Cheng <ycheng@...gle.com>
Cc:	Joe Perches <joe@...ches.com>, David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Neal Cardwell <ncardwell@...gle.com>
Subject: Re: [PATCH v2 net-next] tcp: avoid possible arithmetic overflows

On Sun, 2014-09-21 at 10:46 -0700, Yuchung Cheng wrote:
> On Sat, Sep 20, 2014 at 5:29 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> > From: Eric Dumazet <edumazet@...gle.com>
> >
> > icsk_rto is a 32bit field, and icsk_backoff can reach 15 by default,
> > or more if some sysctl (eg tcp_retries2) are changed.
> >
> > Better use 64bit to perform icsk_rto << icsk_backoff operations
> >
> > As Joe Perches suggested, add a helper for this.
> >
> > From: Eric Dumazet <edumazet@...gle.com>
> Acked-by: Yuchung Cheng <ycheng@...gle.com>
> 
> Maybe also use the new helper for the backoff in tcp_v4_err()?

You mean the following bit ? If yes, I'll incorporate it in v3

Thanks

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 006b045716d8..3b2e49cb2b61 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -430,9 +430,9 @@ void tcp_v4_err(struct sk_buff *icmp_skb, u32 info)
 			break;
 
 		icsk->icsk_backoff--;
-		inet_csk(sk)->icsk_rto = (tp->srtt_us ? __tcp_set_rto(tp) :
-			TCP_TIMEOUT_INIT) << icsk->icsk_backoff;
-		tcp_bound_rto(sk);
+		icsk->icsk_rto = tp->srtt_us ? __tcp_set_rto(tp) :
+					       TCP_TIMEOUT_INIT;
+		icsk->icsk_rto = inet_csk_rto_backoff(icsk, TCP_RTO_MAX);
 
 		skb = tcp_write_queue_head(sk);
 		BUG_ON(!skb);


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