krpc: Ref cnt the client structures for TLS upcalls

A crash occurred during testing, where the client structures had
already been free'd when the upcall thread tried to lock them.

This patch acquires a reference count on both of the structures
and these are released when the upcall is done, so that the
structures cannot be free'd prematurely.  This happened because
the testing is done over a very slow vpn.

Found during a IETF bakeathon testing event this week.

MFC after:	5 days

1 files changed, 8 insertions, 2 deletions

diff --git a/sys/rpc/clnt_vc.c b/sys/rpc/clnt_vc.c
index 386153dc1f36..91556dddebaa 100644
--- a/sys/rpc/clnt_vc.c
+++ b/sys/rpc/clnt_vc.c
@@ -754,6 +754,7 @@ clnt_vc_control(CLIENT *cl, u_int request, void *info)
 	case CLSET_BACKCHANNEL:
 		xprt = (SVCXPRT *)info;
 		if (ct->ct_backchannelxprt == NULL) {
+			SVC_ACQUIRE(xprt);
 			xprt->xp_p2 = ct;
 			if (ct->ct_sslrefno != 0)
 				xprt->xp_tls = RPCTLS_FLAGS_HANDSHAKE;
@@ -767,9 +768,11 @@ clnt_vc_control(CLIENT *cl, u_int request, void *info)
 		ct->ct_sslusec = *p++;
 		ct->ct_sslrefno = *p;
 		if (ct->ct_sslrefno != RPCTLS_REFNO_HANDSHAKE) {
+			/* cl ref cnt is released by clnt_vc_dotlsupcall(). */
+			CLNT_ACQUIRE(cl);
 			mtx_unlock(&ct->ct_lock);
 			/* Start the kthread that handles upcalls. */
-			error = kthread_add(clnt_vc_dotlsupcall, ct,
+			error = kthread_add(clnt_vc_dotlsupcall, cl,
 			    NULL, NULL, 0, 0, "krpctls%u", thrdnum++);
 			if (error != 0)
 				panic("Can't add KRPC thread error %d", error);
@@ -869,6 +872,7 @@ clnt_vc_destroy(CLIENT *cl)
 		mtx_lock(&ct->ct_lock);
 		xprt->xp_p2 = NULL;
 		sx_xunlock(&xprt->xp_lock);
+		SVC_RELEASE(xprt);
 	}
 
 	if (ct->ct_socket) {
@@ -1269,7 +1273,8 @@ clnt_vc_upcallsdone(struct ct_data *ct)
 static void
 clnt_vc_dotlsupcall(void *data)
 {
-	struct ct_data *ct = (struct ct_data *)data;
+	CLIENT *cl = (CLIENT *)data;
+	struct ct_data *ct = (struct ct_data *)cl->cl_private;
 	enum clnt_stat ret;
 	uint32_t reterr;
 
@@ -1306,5 +1311,6 @@ clnt_vc_dotlsupcall(void *data)
 	ct->ct_rcvstate &= ~RPCRCVSTATE_UPCALLTHREAD;
 	wakeup(&ct->ct_sslrefno);
 	mtx_unlock(&ct->ct_lock);
+	CLNT_RELEASE(cl);
 	kthread_exit();
 }