SUNRPC: Fix potential memory corruption

We really should not call rpc_wake_up_queued_task_set_status() with
xprt->snd_task as an argument unless we are certain that is actually an
rpc_task.

Fixes: 0445f92c ("SUNRPC: Fix disconnection races")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

include/linux/sunrpc/xprt.h

@@ -432,6 +432,7 @@ void			xprt_release_write(struct rpc_xprt *, struct rpc_task *);
 #define XPRT_CONGESTED		(9)
 #define XPRT_CWND_WAIT		(10)
 #define XPRT_WRITE_SPACE	(11)
+#define XPRT_SND_IS_COOKIE	(12)
 
 static inline void xprt_set_connected(struct rpc_xprt *xprt)
 {

net/sunrpc/xprt.c

@@ -775,9 +775,9 @@ void xprt_force_disconnect(struct rpc_xprt *xprt)
 	/* Try to schedule an autoclose RPC call */
 	if (test_and_set_bit(XPRT_LOCKED, &xprt->state) == 0)
 		queue_work(xprtiod_workqueue, &xprt->task_cleanup);
-	else if (xprt->snd_task)
+	else if (xprt->snd_task && !test_bit(XPRT_SND_IS_COOKIE, &xprt->state))
 		rpc_wake_up_queued_task_set_status(&xprt->pending,
-				xprt->snd_task, -ENOTCONN);
+						   xprt->snd_task, -ENOTCONN);
 	spin_unlock(&xprt->transport_lock);
 }
 EXPORT_SYMBOL_GPL(xprt_force_disconnect);
@@ -866,6 +866,7 @@ bool xprt_lock_connect(struct rpc_xprt *xprt,
 		goto out;
 	if (xprt->snd_task != task)
 		goto out;
+	set_bit(XPRT_SND_IS_COOKIE, &xprt->state);
 	xprt->snd_task = cookie;
 	ret = true;
 out:
@@ -881,6 +882,7 @@ void xprt_unlock_connect(struct rpc_xprt *xprt, void *cookie)
 	if (!test_bit(XPRT_LOCKED, &xprt->state))
 		goto out;
 	xprt->snd_task =NULL;
+	clear_bit(XPRT_SND_IS_COOKIE, &xprt->state);
 	xprt->ops->release_xprt(xprt, NULL);
 	xprt_schedule_autodisconnect(xprt);
 out: