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tcp: fix fastopen races vs lockless listener

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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 7c85af8810 ("tcp: avoid reorders for TFO passive connections")

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet
2015-10-04 21:08:07 -07:00
committed by David S. Miller
parent 3e087caa23
commit 7656d842de
2 changed files with 12 additions and 20 deletions
Download Patch File Download Diff File Expand all files Collapse all files
net/ipv4/tcp_input.c
+5 -1
View File
@@ -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;