rds: tcp: Set linger when rejecting an incoming conn in rds_tcp_accept_one

Each time we get an incoming SYN to the RDS_TCP_PORT, the TCP
layer accepts the connection and then the rds_tcp_accept_one()
callback is invoked to process the incoming connection.

rds_tcp_accept_one() may reject the incoming syn for a number of
reasons, e.g., commit 1a0e100fb2c9 ("RDS: TCP: Force every connection
to be initiated by numerically smaller IP address"), or because
we are getting spammed by a malicious node that is triggering
a flood of connection attempts to RDS_TCP_PORT. If the incoming
syn is rejected, no data would have been sent on the TCP socket,
and we do not need to be in TIME_WAIT state, so we set linger on
the TCP socket before closing, thereby closing the socket efficiently
with a RST.

Signed-off-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Tested-by: Imanti Mendez <imanti.mendez@oracle.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/rds/tcp_listen.c b/net/rds/tcp_listen.c
index f9c6312..df291ac 100644 (file)
--- a/net/rds/tcp_listen.c
+++ b/net/rds/tcp_listen.c
@@ -112,6 +112,17 @@ struct rds_tcp_connection *rds_tcp_accept_one_path(struct rds_connection *conn)
        return NULL;
 }
 
+static void rds_tcp_set_linger(struct socket *sock)
+{
+       struct linger no_linger = {
+               .l_onoff = 1,
+               .l_linger = 0,
+       };
+
+       kernel_setsockopt(sock, SOL_SOCKET, SO_LINGER,
+                         (char *)&no_linger, sizeof(no_linger));
+}
+
 int rds_tcp_accept_one(struct socket *sock)
 {
        struct socket *new_sock = NULL;
@@ -183,7 +194,13 @@ int rds_tcp_accept_one(struct socket *sock)
        ret = 0;
        goto out;
 rst_nsk:
-       /* reset the newly returned accept sock and bail */
+       /* reset the newly returned accept sock and bail.
+        * It is safe to set linger on new_sock because the RDS connection
+        * has not been brought up on new_sock, so no RDS-level data could
+        * be pending on it. By setting linger, we achieve the side-effect
+        * of avoiding TIME_WAIT state on new_sock.
+        */
+       rds_tcp_set_linger(new_sock);
        kernel_sock_shutdown(new_sock, SHUT_RDWR);
        ret = 0;
 out: