tcp: fastopen: limit max_qlen

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@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 1 deletions

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 5dce9705fe84..c906f4534581 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -392,8 +392,9 @@ 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)