[patch 17/36] TCP: MTUprobe: fix potential sk_send_head corruption

[Greg KH]

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

------------------
From: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxx>

[TCP] MTUprobe: fix potential sk_send_head corruption

[ Upstream commit: 6e42141009ff18297fe19d19296738b742f861db ]

When the abstraction functions got added, conversion here was
made incorrectly. As a result, the skb may end up pointing
to skb which got included to the probe skb and then was freed.
For it to trigger, however, skb_transmit must fail sending as
well.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 include/net/tcp.h     |    3 +++
 net/ipv4/tcp_output.c |    1 -
 2 files changed, 3 insertions(+), 1 deletion(-)

--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1258,6 +1258,9 @@ static inline void tcp_insert_write_queu
 						  struct sock *sk)
 {
 	__skb_insert(new, skb->prev, skb, &sk->sk_write_queue);
+
+	if (sk->sk_send_head == skb)
+		sk->sk_send_head = new;
 }
 
 static inline void tcp_unlink_write_queue(struct sk_buff *skb, struct sock *sk)
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1279,7 +1279,6 @@ static int tcp_mtu_probe(struct sock *sk
 
 	skb = tcp_send_head(sk);
 	tcp_insert_write_queue_before(nskb, skb, sk);
-	tcp_advance_send_head(sk, skb);
 
 	TCP_SKB_CB(nskb)->seq = TCP_SKB_CB(skb)->seq;
 	TCP_SKB_CB(nskb)->end_seq = TCP_SKB_CB(skb)->seq + probe_size;

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