netdev - [PATCH net-next] tcp: fastopen: limit max

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Date:	Tue, 20 Oct 2015 13:17:40 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev <netdev@...r.kernel.org>, Yuchung Cheng <ycheng@...gle.com>
Subject: [PATCH net-next] tcp: fastopen: limit max_qlen

From: Eric Dumazet <edumazet@...gle.com>

Allowing an application to set whatever limit for
the list of recently RST fastopen sessions [1] is not wise,
as it open ways to deplete kernel memory.

Cap the user provided limit by somaxconn sysctl,
like listen() backlog.

[1] https://tools.ietf.org/html/rfc7413#section-5.1

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 include/linux/tcp.h |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 86a7edaa6797..80ba0f7c0518 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -385,8 +385,9 @@ static inline bool tcp_passive_fastopen(const struct sock *sk)
 static inline void fastopen_queue_tune(struct sock *sk, int backlog)
 {
 	struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;
+	int somaxconn = READ_ONCE(sock_net(sk)->core.sysctl_somaxconn);
 
-	queue->fastopenq.max_qlen = backlog;
+	queue->fastopenq.max_qlen = min_t(unsigned int, backlog, somaxconn);
 }
 
 static inline void tcp_saved_syn_free(struct tcp_sock *tp)


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