tcp: fix fastopen races vs lockless listener
There are multiple races that need fixes :
1) skb_get() + queue skb + kfree_skb() is racy
An accept() can be done on another cpu, data consumed immediately.
tcp_recvmsg() uses __kfree_skb() as it is assumed all skb found in
socket receive queue are private.
Then the kfree_skb() in tcp_rcv_state_process() uses an already freed skb
2) tcp_reqsk_record_syn() needs to be done before tcp_try_fastopen()
for the same reasons.
3) We want to send the SYNACK before queueing child into accept queue,
otherwise we might reintroduce the ooo issue fixed in
commit 7c85af881044 ("tcp: avoid reorders for TFO passive connections")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/tcp_fastopen.c b/net/ipv4/tcp_fastopen.c
index 410ac48..93396bf 100644
--- a/net/ipv4/tcp_fastopen.c
+++ b/net/ipv4/tcp_fastopen.c
@@ -168,8 +168,6 @@
TCP_TIMEOUT_INIT, TCP_RTO_MAX);
atomic_set(&req->rsk_refcnt, 2);
- /* Add the child socket directly into the accept queue */
- inet_csk_reqsk_queue_add(sk, req, child);
/* Now finish processing the fastopen child socket. */
inet_csk(child)->icsk_af_ops->rebuild_header(child);
@@ -178,12 +176,10 @@
tcp_init_metrics(child);
tcp_init_buffer_space(child);
- /* Queue the data carried in the SYN packet. We need to first
- * bump skb's refcnt because the caller will attempt to free it.
- * Note that IPv6 might also have used skb_get() trick
- * in tcp_v6_conn_request() to keep this SYN around (treq->pktopts)
- * So we need to eventually get a clone of the packet,
- * before inserting it in sk_receive_queue.
+ /* Queue the data carried in the SYN packet.
+ * We used to play tricky games with skb_get().
+ * With lockless listener, it is a dead end.
+ * Do not think about it.
*
* XXX (TFO) - we honor a zero-payload TFO request for now,
* (any reason not to?) but no need to queue the skb since
@@ -191,12 +187,7 @@
*/
end_seq = TCP_SKB_CB(skb)->end_seq;
if (end_seq != TCP_SKB_CB(skb)->seq + 1) {
- struct sk_buff *skb2;
-
- if (unlikely(skb_shared(skb)))
- skb2 = skb_clone(skb, GFP_ATOMIC);
- else
- skb2 = skb_get(skb);
+ struct sk_buff *skb2 = skb_clone(skb, GFP_ATOMIC);
if (likely(skb2)) {
skb_dst_drop(skb2);
@@ -214,12 +205,9 @@
}
}
tcp_rsk(req)->rcv_nxt = tp->rcv_nxt = end_seq;
- sk->sk_data_ready(sk);
- bh_unlock_sock(child);
- /* Note: sock_put(child) will be done by tcp_conn_request()
- * after SYNACK packet is sent.
+ /* tcp_conn_request() is sending the SYNACK,
+ * and queues the child into listener accept queue.
*/
- WARN_ON(!req->sk);
return child;
}