[PATCH net-2.6 (2nd try)] [TCP] MTUprobe: fix potential sk_send_head corruption

[Ilpo Järvinen]

Please ignore the previous version, it had an rbtree artifact which made 
it to not apply cleanly, here's the corrected version:

--
[PATCH] [TCP] MTUprobe: fix potential sk_send_head corruption

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 <[EMAIL PROTECTED]>
---
 include/net/tcp.h     |    3 +++
 net/ipv4/tcp_output.c |    1 -
 2 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 1bceca8..f0c5e7a 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1290,6 +1290,9 @@ static inline void tcp_insert_write_queue_before(struct 
sk_buff *new,
                                                  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)
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index b0ece43..30d6737 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1346,7 +1346,6 @@ 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;
-- 
1.5.0.6