In the current world order, solisten() implements the state transition of

a socket from a regular socket to a listening socket able to accept new
connections.  As part of this state transition, solisten() calls into the
protocol to update protocol-layer state.  There were several bugs in this
implementation that could result in a race wherein a TCP SYN received
in the interval between the protocol state transition and the shortly
following socket layer transition would result in a panic in the TCP code,
as the socket would be in the TCPS_LISTEN state, but the socket would not
have the SO_ACCEPTCONN flag set.

This change does the following:

- Pushes the socket state transition from the socket layer solisten() to
  to socket "library" routines called from the protocol.  This permits
  the socket routines to be called while holding the protocol mutexes,
  preventing a race exposing the incomplete socket state transition to TCP
  after the TCP state transition has completed.  The check for a socket
  layer state transition is performed by solisten_proto_check(), and the
  actual transition is performed by solisten_proto().

- Holds the socket lock for the duration of the socket state test and set,
  and over the protocol layer state transition, which is now possible as
  the socket lock is acquired by the protocol layer, rather than vice
  versa.  This prevents additional state related races in the socket
  layer.

This permits the dual transition of socket layer and protocol layer state
to occur while holding locks for both layers, making the two changes
atomic with respect to one another.  Similar changes are likely require
elsewhere in the socket/protocol code.

Reported by:		Peter Holm <peter@holm.cc>
Review and fixes from:	emax, Antoine Brodin <antoine.brodin@laposte.net>
Philosophical head nod:	gnn

4 files changed, 18 insertions, 6 deletions

diff --git a/sys/netatm/atm_cm.c b/sys/netatm/atm_cm.c
index 2da05b3..60bf482 100644
--- a/sys/netatm/atm_cm.c
+++ b/sys/netatm/atm_cm.c
@@ -524,6 +524,7 @@ done:
  * atm_cm_release().
  *
  * Arguments:
+ *	so	optional socket pointer -- if present, will set listen state
  *	epp	pointer to endpoint definition structure
  *	token	endpoint's listen instance token
  *	ap	pointer to listening connection attributes
@@ -535,7 +536,8 @@ done:
  *
  */
 int
-atm_cm_listen(epp, token, ap, copp)
+atm_cm_listen(so, epp, token, ap, copp)
+	struct socket	*so;
 	Atm_endpoint	*epp;
 	void		*token;
 	Atm_attributes	*ap;
@@ -718,7 +720,13 @@ atm_cm_listen(epp, token, ap, copp)
 	/*
 	 * Now try to register the listening connection
 	 */
+	if (so != NULL)
+		SOCK_LOCK(so);
 	s = splnet();
+	if (so != NULL)
+		err = solisten_proto_check(so);
+	if (err)
+		goto donex;
 	if (atm_cm_match(cop->co_lattr, NULL) != NULL) {
 		/*
 		 * Can't have matching listeners
@@ -728,9 +736,13 @@ atm_cm_listen(epp, token, ap, copp)
 	}
 	cop->co_state = COS_LISTEN;
 	LINK2TAIL(cop, Atm_connection, atm_listen_queue, co_next);
+	if (so != NULL)
+		solisten_proto(so);
 
 donex:
 	(void) splx(s);
+	if (so != NULL)
+		SOCK_UNLOCK(so);
 
 done:
 	if (err) {
diff --git a/sys/netatm/atm_socket.c b/sys/netatm/atm_socket.c
index a851537..37ea86d 100644
--- a/sys/netatm/atm_socket.c
+++ b/sys/netatm/atm_socket.c
@@ -350,7 +350,7 @@ atm_sock_listen(so, epp)
 	/*
 	 * Start listening for incoming calls
 	 */
-	return (atm_cm_listen(epp, atp, &atp->atp_attr, &atp->atp_conn));
+	return (atm_cm_listen(so, epp, atp, &atp->atp_attr, &atp->atp_conn));
 }
 
 
diff --git a/sys/netatm/atm_var.h b/sys/netatm/atm_var.h
index e014bf6..3332c92 100644
--- a/sys/netatm/atm_var.h
+++ b/sys/netatm/atm_var.h
@@ -81,8 +81,8 @@ void		atm_aal5_init(void);
 	/* atm_cm.c */
 int		atm_cm_connect(Atm_endpoint *, void *, Atm_attributes *,
 			Atm_connection **);
-int		atm_cm_listen(Atm_endpoint *, void *, Atm_attributes *,
-			Atm_connection **);
+int		atm_cm_listen(struct socket *, Atm_endpoint *, void *,
+			Atm_attributes *, Atm_connection **);
 int		atm_cm_addllc(Atm_endpoint *, void *, struct attr_llc *,
 			Atm_connection *, Atm_connection **);
 int		atm_cm_addparty(Atm_connection *, int, struct t_atm_sap *);
diff --git a/sys/netatm/ipatm/ipatm_load.c b/sys/netatm/ipatm/ipatm_load.c
index 3df5e8f..638c0ce 100644
--- a/sys/netatm/ipatm/ipatm_load.c
+++ b/sys/netatm/ipatm/ipatm_load.c
@@ -522,8 +522,8 @@ ipatm_start()
 		/*
 		 * Now start listening
 		 */
-		if ((err = atm_cm_listen(&ipatm_endpt, (void *)(intptr_t)i,
-				&ipatm_listeners[i].attr,
+		if ((err = atm_cm_listen(NULL, &ipatm_endpt,
+				(void *)(intptr_t)i, &ipatm_listeners[i].attr,
 				&ipatm_listeners[i].conn)) != 0)
 			goto done;
 	}