[PATCH 5.6 15/41] mptcp: fix unblocking connect()

Greg Kroah-Hartman
2020-06-09T17:56:21Z

From: Paolo Abeni <pabeni@redhat.com>

[ Upstream commit 41be81a8d3d09acb9033799938306349328861f9 ]

Currently unblocking connect() on MPTCP sockets fails frequently.
If mptcp_stream_connect() is invoked to complete a previously
attempted unblocking connection, it will still try to create
the first subflow via __mptcp_socket_create(). If the 3whs is
completed and the 'can_ack' flag is already set, the latter
will fail with -EINVAL.

This change addresses the issue checking for pending connect and
delegating the completion to the first subflow. Additionally
do msk addresses and sk_state changes only when needed.

Fixes: 2303f994b3e1 ("mptcp: Associate MPTCP context with TCP socket")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/mptcp/protocol.c | 20 ++++++++++++++++++--
1 file changed, 18 insertions(+), 2 deletions(-)

--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -920,6 +920,14 @@ static int mptcp_stream_connect(struct s
int err;

lock_sock(sock->sk);
+ if (sock->state != SS_UNCONNECTED && msk->subflow) {
+ /* pending connection or invalid state, let existing subflow
+ * cope with that
+ */
+ ssock = msk->subflow;
+ goto do_connect;
+ }
+
ssock = __mptcp_socket_create(msk, TCP_SYN_SENT);
if (IS_ERR(ssock)) {
err = PTR_ERR(ssock);
@@ -934,9 +942,17 @@ static int mptcp_stream_connect(struct s
mptcp_subflow_ctx(ssock->sk)->request_mptcp = 0;
#endif

+do_connect:
err = ssock->ops->connect(ssock, uaddr, addr_len, flags);
- inet_sk_state_store(sock->sk, inet_sk_state_load(ssock->sk));
- mptcp_copy_inaddrs(sock->sk, ssock->sk);
+ sock->state = ssock->state;
+
+ /* on successful connect, the msk state will be moved to established by
+ * subflow_finish_connect()
+ */
+ if (!err || err == EINPROGRESS)
+ mptcp_copy_inaddrs(sock->sk, ssock->sk);
+ else
+ inet_sk_state_store(sock->sk, inet_sk_state_load(ssock->sk));

unlock:
release_sock(sock->sk);