netdev - Re: [PATCH] tcp: fix tcp_trim_head() to adjust segment count with skb MSS

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: <20120130.124338.2160187165526498508.davem@davemloft.net>
Date:	Mon, 30 Jan 2012 12:43:38 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	ilpo.jarvinen@...sinki.fi
Cc:	ncardwell@...gle.com, netdev@...r.kernel.org, nanditad@...gle.com,
	ycheng@...gle.com, therbert@...gle.com
Subject: Re: [PATCH] tcp: fix tcp_trim_head() to adjust segment count with
 skb MSS

From: "Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
Date: Mon, 30 Jan 2012 09:08:51 +0200 (EET)

> On Sat, 28 Jan 2012, Neal Cardwell wrote:
> 
>> This commit fixes tcp_trim_head() to recalculate the number of
>> segments in the skb with the skb's existing MSS, so trimming the head
>> causes the skb segment count to be monotonically non-increasing - it
>> should stay the same or go down, but not increase.
>> 
>> Previously tcp_trim_head() used the current MSS of the connection. But
>> if there was a decrease in MSS between original transmission and ACK
>> (e.g. due to PMTUD), this could cause tcp_trim_head() to
>> counter-intuitively increase the segment count when trimming bytes off
>> the head of an skb. This violated assumptions in tcp_tso_acked() that
>> tcp_trim_head() only decreases the packet count, so that packets_acked
>> in tcp_tso_acked() could underflow, leading tcp_clean_rtx_queue() to
>> pass u32 pkts_acked values as large as 0xffffffff to
>> ca_ops->pkts_acked().
>> 
>> As an aside, if tcp_trim_head() had really wanted the skb to reflect
>> the current MSS, it should have called tcp_set_skb_tso_segs()
>> unconditionally, since a decrease in MSS would mean that a
>> single-packet skb should now be sliced into multiple segments.
>> 
>> Signed-off-by: Neal Cardwell <ncardwell@...gle.com>
 ...
> Acked-by: Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>

Applied, thanks everyone.
--
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