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 <eduma...@google.com>
---
net/ipv4/tcp_fastopen.c | 26 +++++++-------------------
net/ipv4/tcp_input.c | 6 +++++-
2 files changed, 12 insertions(+), 20 deletions(-)
diff --git a/net/ipv4/tcp_fastopen.c b/net/ipv4/tcp_fastopen.c
index 410ac481fda0..93396bf7b475 100644
--- a/net/ipv4/tcp_fastopen.c
+++ b/net/ipv4/tcp_fastopen.c
@@ -168,8 +168,6 @@ static struct sock *tcp_fastopen_create_child(struct sock
*sk,
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 @@ static struct sock *tcp_fastopen_create_child(struct sock
*sk,
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 @@ static struct sock *tcp_fastopen_create_child(struct sock
*sk,
*/
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 @@ static struct sock *tcp_fastopen_create_child(struct sock
*sk,
}
}
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;
}
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 27108757c310..a95c8eb04ff7 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -6229,12 +6229,16 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
tcp_rsk(req)->txhash = net_tx_rndhash();
tcp_openreq_init_rwin(req, sk, dst);
if (!want_cookie) {
- fastopen_sk = tcp_try_fastopen(sk, skb, req, &foc, dst);
tcp_reqsk_record_syn(sk, req, skb);
+ fastopen_sk = tcp_try_fastopen(sk, skb, req, &foc, dst);
}
if (fastopen_sk) {
af_ops->send_synack(fastopen_sk, dst, &fl, req,
skb_get_queue_mapping(skb), &foc, false);
+ /* Add the child socket directly into the accept queue */
+ inet_csk_reqsk_queue_add(sk, req, fastopen_sk);
+ sk->sk_data_ready(sk);
+ bh_unlock_sock(fastopen_sk);
sock_put(fastopen_sk);
} else {
tcp_rsk(req)->tfo_listener = false;
--
2.6.0.rc2.230.g3dd15c0
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