Subject: [PATCH 20/38] tcp: handle inet_csk_reqsk_queue_add() failures

From: Guillaume Nault <[email-masked]>
Date: Fri, 8 Mar 2019 22:09:47 +0100

[  Upstream commit 9d3e1368bb45893a75a5dfb7cd21fdebfa6b47af ]

Commit 7716682cc58e ("tcp/dccp: fix another race at listener
dismantle") let inet_csk_reqsk_queue_add() fail, and adjusted
{tcp,dccp}_check_req() accordingly. However, TFO and syncookies
weren't modified, thus leaking allocated resources on error.

Contrary to tcp_check_req(), in both syncookies and TFO cases,
we need to drop the request socket. Also, since the child socket is
created with inet_csk_clone_lock(), we have to unlock it and drop an
extra reference (->sk_refcount is initially set to 2 and
inet_csk_reqsk_queue_add() drops only one ref).

For TFO, we also need to revert the work done by tcp_try_fastopen()
(with reqsk_fastopen_remove()).

Fixes: 7716682cc58e ("tcp/dccp: fix another race at listener dismantle")
Signed-off-by: Guillaume Nault <[email-masked]>
Signed-off-by: Eric Dumazet <[email-masked]>
Signed-off-by: David S. Miller <[email-masked]>
---
 net/ipv4/syncookies.c | 7 ++++++-
 net/ipv4/tcp_input.c  | 8 +++++++-
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index 606f868d9f3f..e531344611a0 100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -216,7 +216,12 @@ struct sock *tcp_get_cookie_sock(struct sock *sk, struct sk_buff *skb,
 		refcount_set(&req->rsk_refcnt, 1);
 		tcp_sk(child)->tsoffset = tsoff;
 		sock_rps_save_rxhash(child, skb);
-		inet_csk_reqsk_queue_add(sk, req, child);
+		if (!inet_csk_reqsk_queue_add(sk, req, child)) {
+			bh_unlock_sock(child);
+			sock_put(child);
+			child = NULL;
+			reqsk_put(req);
+		}
 	} else {
 		reqsk_free(req);
 	}
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index a9d9555a973f..1ceb41cf785f 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -6511,7 +6511,13 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops,
 		af_ops->send_synack(fastopen_sk, dst, &fl, req,
 				    &foc, TCP_SYNACK_FASTOPEN);
 		/* Add the child socket directly into the accept queue */
-		inet_csk_reqsk_queue_add(sk, req, fastopen_sk);
+		if (!inet_csk_reqsk_queue_add(sk, req, fastopen_sk)) {
+			reqsk_fastopen_remove(fastopen_sk, req, false);
+			bh_unlock_sock(fastopen_sk);
+			sock_put(fastopen_sk);
+			reqsk_put(req);
+			goto drop;
+		}
 		sk->sk_data_ready(sk);
 		bh_unlock_sock(fastopen_sk);
 		sock_put(fastopen_sk);
-- 
2.20.1