[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 <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 3 insertions, 1 deletions

diff --git a/include/net/tcp.h b/include/net/tcp.h
index d695cea7730d..cb5b033e0e59 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1288,6 +1288,9 @@ 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 324b4207254a..e48e28e7d539 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1352,7 +1352,6 @@ 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;