netdev - [PATCH net 1/3] mptcp: handle mptcp listener destruction via rcu

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Message-Id: <3acf989202f0bf82d974611d0fda7052de8d6ec3.1587389294.git.pabeni@redhat.com>
Date:   Mon, 20 Apr 2020 16:25:04 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     netdev@...r.kernel.org
Cc:     Mat Martineau <mathew.j.martineau@...ux.intel.com>,
        Matthieu Baerts <matthieu.baerts@...sares.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Christoph Paasch <cpaasch@...le.com>,
        Florian Westphal <fw@...len.de>
Subject: [PATCH net 1/3] mptcp: handle mptcp listener destruction via rcu

From: Florian Westphal <fw@...len.de>

Following splat can occur during self test:

 BUG: KASAN: use-after-free in subflow_data_ready+0x156/0x160
 Read of size 8 at addr ffff888100c35c28 by task mptcp_connect/4808

  subflow_data_ready+0x156/0x160
  tcp_child_process+0x6a3/0xb30
  tcp_v4_rcv+0x2231/0x3730
  ip_protocol_deliver_rcu+0x5c/0x860
  ip_local_deliver_finish+0x220/0x360
  ip_local_deliver+0x1c8/0x4e0
  ip_rcv_finish+0x1da/0x2f0
  ip_rcv+0xd0/0x3c0
  __netif_receive_skb_one_core+0xf5/0x160
  __netif_receive_skb+0x27/0x1c0
  process_backlog+0x21e/0x780
  net_rx_action+0x35f/0xe90
  do_softirq+0x4c/0x50
  [..]

This occurs when accessing subflow_ctx->conn.

Problem is that tcp_child_process() calls listen sockets'
sk_data_ready() notification, but it doesn't hold the listener
lock.  Another cpu calling close() on the listener will then cause
transition of refcount to 0.

Fixes: 58b09919626bf ("mptcp: create msk early")
Signed-off-by: Florian Westphal <fw@...len.de>
Signed-off-by: Paolo Abeni <pabeni@...hat.com>
---
 net/mptcp/protocol.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index b2d2193453bc..d275c1e827fe 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -1391,6 +1391,7 @@ struct sock *mptcp_sk_clone(const struct sock *sk, struct request_sock *req)
 		msk->ack_seq = ack_seq;
 	}
 
+	sock_reset_flag(nsk, SOCK_RCU_FREE);
 	/* will be fully established after successful MPC subflow creation */
 	inet_sk_state_store(nsk, TCP_SYN_RECV);
 	bh_unlock_sock(nsk);
@@ -1792,6 +1793,8 @@ static int mptcp_listen(struct socket *sock, int backlog)
 		goto unlock;
 	}
 
+	sock_set_flag(sock->sk, SOCK_RCU_FREE);
+
 	err = ssock->ops->listen(ssock, backlog);
 	inet_sk_state_store(sock->sk, inet_sk_state_load(ssock->sk));
 	if (!err)
-- 
2.21.1