linux-kernel - [79/89] 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] [thread-next>] [day] [month] [year] [list]

Message-Id: <20120201210050.821593243@clark.kroah.org>
Date:	Wed, 01 Feb 2012 13:00:43 -0800
From:	Greg KH <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Neal Cardwell <ncardwell@...gle.com>,
	Nandita Dukkipati <nanditad@...gle.com>,
	Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>,
	"David S. Miller" <davem@...emloft.net>
Subject: [79/89] tcp: fix tcp_trim_head() to adjust segment count with skb MSS

3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Neal Cardwell <ncardwell@...gle.com>

[ Upstream commit 5b35e1e6e9ca651e6b291c96d1106043c9af314a ]

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: Nandita Dukkipati <nanditad@...gle.com>
Acked-by: Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/ipv4/tcp_output.c |    6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1138,11 +1138,9 @@ int tcp_trim_head(struct sock *sk, struc
 	sk_mem_uncharge(sk, len);
 	sock_set_flag(sk, SOCK_QUEUE_SHRUNK);

-	/* Any change of skb->len requires recalculation of tso
-	 * factor and mss.
-	 */
+	/* Any change of skb->len requires recalculation of tso factor. */
 	if (tcp_skb_pcount(skb) > 1)
-		tcp_set_skb_tso_segs(sk, skb, tcp_current_mss(sk));
+		tcp_set_skb_tso_segs(sk, skb, tcp_skb_mss(skb));

 	return 0;
 }

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/