linux-kernel - [ 64/80] tcp: tcp_replace_ts_recent() should not be called from tcp_validate

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Message-Id: <20130109201508.632338664@linuxfoundation.org>
Date:	Wed,  9 Jan 2013 12:35:56 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	alan@...rguk.ukuu.org.uk, Eric Dumazet <edumazet@...gle.com>,
	Neal Cardwell <ncardwell@...gle.com>,
	Yuchung Cheng <ycheng@...gle.com>,
	Nandita Dukkipati <nanditad@...gle.com>,
	"H.K. Jerry Chu" <hkchu@...gle.com>,
	Romain Francoise <romain@...bokech.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: [ 64/80] tcp: tcp_replace_ts_recent() should not be called from tcp_validate_incoming()

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

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


From: Eric Dumazet <edumazet@...gle.com>

[ Upstream commit bd090dfc634ddd711a5fbd0cadc6e0ab4977bcaf ]

We added support for RFC 5961 in latest kernels but TCP fails
to perform exhaustive check of ACK sequence.

We can update our view of peer tsval from a frame that is
later discarded by tcp_ack()

This makes timestamps enabled sessions vulnerable to injection of
a high tsval : peers start an ACK storm, since the victim
sends a dupack each time it receives an ACK from the other peer.

As tcp_validate_incoming() is called before tcp_ack(), we should
not peform tcp_replace_ts_recent() from it, and let callers do it
at the right time.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Neal Cardwell <ncardwell@...gle.com>
Cc: Yuchung Cheng <ycheng@...gle.com>
Cc: Nandita Dukkipati <nanditad@...gle.com>
Cc: H.K. Jerry Chu <hkchu@...gle.com>
Cc: Romain Francoise <romain@...bokech.com>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/ipv4/tcp_input.c |   15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5337,11 +5337,6 @@ static bool tcp_validate_incoming(struct
 		goto discard;
 	}
 
-	/* ts_recent update must be made after we are sure that the packet
-	 * is in window.
-	 */
-	tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
-
 	/* step 3: check security and precedence [ignored] */
 
 	/* step 4: Check for a SYN
@@ -5576,6 +5571,11 @@ step5:
 	if (th->ack && tcp_ack(sk, skb, FLAG_SLOWPATH) < 0)
 		goto discard;
 
+	/* ts_recent update must be made after we are sure that the packet
+	 * is in window.
+	 */
+	tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
+
 	tcp_rcv_rtt_measure_ts(sk, skb);
 
 	/* Process urgent data. */
@@ -6046,6 +6046,11 @@ int tcp_rcv_state_process(struct sock *s
 	} else
 		goto discard;
 
+	/* ts_recent update must be made after we are sure that the packet
+	 * is in window.
+	 */
+	tcp_replace_ts_recent(tp, TCP_SKB_CB(skb)->seq);
+
 	/* step 6: check the URG bit */
 	tcp_urg(sk, skb, th);
 


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