netdev - Re: [PATCH] tcp: cubic: fix overflow error in bictcp

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-Id: <20130807.103630.161949444720355649.davem@davemloft.net>
Date:	Wed, 07 Aug 2013 10:36:30 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	netdev@...r.kernel.org, ncardwell@...gle.com, vanj@...gle.com,
	stephen@...workplumber.org, ycheng@...gle.com
Subject: Re: [PATCH] tcp: cubic: fix overflow error in bictcp_update()

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Mon, 05 Aug 2013 17:10:15 -0700

> From: Eric Dumazet <edumazet@...gle.com>
> 
> commit 17a6e9f1aa9 ("tcp_cubic: fix clock dependency") added an
> overflow error in bictcp_update() in following code :
> 
> /* change the unit from HZ to bictcp_HZ */
> t = ((tcp_time_stamp + msecs_to_jiffies(ca->delay_min>>3) -
>       ca->epoch_start) << BICTCP_HZ) / HZ;
> 
> Because msecs_to_jiffies() being unsigned long, compiler does
> implicit type promotion.
> 
> We really want to constrain (tcp_time_stamp - ca->epoch_start)
> to a signed 32bit value, or else 't' has unexpected high values.
> 
> This bugs triggers an increase of retransmit rates ~24 days after
> boot [1], as the high order bit of tcp_time_stamp flips.
> 
> [1] for hosts with HZ=1000
> 
> Big thanks to Van Jacobson for spotting this problem.
> 
> Diagnosed-by: Van Jacobson <vanj@...gle.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Applied and queued up for -stable.
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html