netdev - [PATCH net 4/7] mptcp: fix race in incoming ADD

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Date:   Fri, 18 Feb 2022 13:35:41 -0800
From:   Mat Martineau <mathew.j.martineau@...ux.intel.com>
To:     netdev@...r.kernel.org
Cc:     Paolo Abeni <pabeni@...hat.com>, davem@...emloft.net,
        kuba@...nel.org, matthieu.baerts@...sares.net,
        geliang.tang@...e.com, mptcp@...ts.linux.dev,
        Mat Martineau <mathew.j.martineau@...ux.intel.com>
Subject: [PATCH net 4/7] mptcp: fix race in incoming ADD_ADDR option processing

From: Paolo Abeni <pabeni@...hat.com>

If an MPTCP endpoint received multiple consecutive incoming
ADD_ADDR options, mptcp_pm_add_addr_received() can overwrite
the current remote address value after the PM lock is released
in mptcp_pm_nl_add_addr_received() and before such address
is echoed.

Fix the issue caching the remote address value a little earlier
and always using the cached value after releasing the PM lock.

Fixes: f7efc7771eac ("mptcp: drop argument port from mptcp_pm_announce_addr")
Reviewed-by: Matthieu Baerts <matthieu.baerts@...sares.net>
Signed-off-by: Paolo Abeni <pabeni@...hat.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@...ux.intel.com>
---
 net/mptcp/pm_netlink.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
index 82f82a513f5b..4b5d795383cd 100644
--- a/net/mptcp/pm_netlink.c
+++ b/net/mptcp/pm_netlink.c
@@ -660,6 +660,7 @@ static void mptcp_pm_nl_add_addr_received(struct mptcp_sock *msk)
 	unsigned int add_addr_accept_max;
 	struct mptcp_addr_info remote;
 	unsigned int subflows_max;
+	bool reset_port = false;
 	int i, nr;
 
 	add_addr_accept_max = mptcp_pm_get_add_addr_accept_max(msk);
@@ -669,15 +670,19 @@ static void mptcp_pm_nl_add_addr_received(struct mptcp_sock *msk)
 		 msk->pm.add_addr_accepted, add_addr_accept_max,
 		 msk->pm.remote.family);
 
-	if (lookup_subflow_by_daddr(&msk->conn_list, &msk->pm.remote))
+	remote = msk->pm.remote;
+	if (lookup_subflow_by_daddr(&msk->conn_list, &remote))
 		goto add_addr_echo;
 
+	/* pick id 0 port, if none is provided the remote address */
+	if (!remote.port) {
+		reset_port = true;
+		remote.port = sk->sk_dport;
+	}
+
 	/* connect to the specified remote address, using whatever
 	 * local address the routing configuration will pick.
 	 */
-	remote = msk->pm.remote;
-	if (!remote.port)
-		remote.port = sk->sk_dport;
 	nr = fill_local_addresses_vec(msk, addrs);
 
 	msk->pm.add_addr_accepted++;
@@ -690,8 +695,12 @@ static void mptcp_pm_nl_add_addr_received(struct mptcp_sock *msk)
 		__mptcp_subflow_connect(sk, &addrs[i], &remote);
 	spin_lock_bh(&msk->pm.lock);
 
+	/* be sure to echo exactly the received address */
+	if (reset_port)
+		remote.port = 0;
+
 add_addr_echo:
-	mptcp_pm_announce_addr(msk, &msk->pm.remote, true);
+	mptcp_pm_announce_addr(msk, &remote, true);
 	mptcp_pm_nl_addr_send_ack(msk);
 }
 
-- 
2.35.1