linux-kernel - [026/140] tcp: fix crash in tcp_xmit_retransmit

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Date:	Fri, 30 Jul 2010 10:29:51 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Ilpo JÃ€rvinen <ilpo.jarvinen@...sinki.fi>,
	"David S. Miller" <davem@...emloft.net>
Subject: [026/140] tcp: fix crash in tcp_xmit_retransmit_queue

2.6.33-stable review patch.  If anyone has any objections, please let us know.

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

From: Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>

commit 45e77d314585869dfe43c82679f7e08c9b35b898 upstream.

It can happen that there are no packets in queue while calling
tcp_xmit_retransmit_queue(). tcp_write_queue_head() then returns
NULL and that gets deref'ed to get sacked into a local var.

There is no work to do if no packets are outstanding so we just
exit early.

This oops was introduced by 08ebd1721ab8fd (tcp: remove tp->lost_out
guard to make joining diff nicer).

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
Reported-by: Lennart Schulte <lennart.schulte@...s.rwth-aachen.de>
Tested-by: Lennart Schulte <lennart.schulte@...s.rwth-aachen.de>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 net/ipv4/tcp_output.c |    3 +++
 1 file changed, 3 insertions(+)

--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2203,6 +2203,9 @@ void tcp_xmit_retransmit_queue(struct so
 	int mib_idx;
 	int fwd_rexmitting = 0;

+	if (!tp->packets_out)
+		return;
+
 	if (!tp->lost_out)
 		tp->retransmit_high = tp->snd_una;

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