target/user: Don't free expired command when time out

Which would result in NPE after when userspace connected again.

Expired command would be freed either when handling command(by userspace),
or when device was tearing down
Reviewed-by: Andy Grover <agrover@redhat.com>
Signed-off-by: Sheng Yang <sheng@yasker.org>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/target/target_core_user.c

@@ -560,9 +560,13 @@ static void tcmu_handle_completion(struct tcmu_cmd *cmd, struct tcmu_cmd_entry *
 	struct tcmu_dev *udev = cmd->tcmu_dev;
 
 	if (test_bit(TCMU_CMD_BIT_EXPIRED, &cmd->flags)) {
-		/* cmd has been completed already from timeout, just reclaim data
-		   ring space */
+		/*
+		 * cmd has been completed already from timeout, just reclaim
+		 * data ring space and free cmd
+		 */
 		free_data_area(udev, cmd);
+
+		kmem_cache_free(tcmu_cmd_cache, cmd);
 		return;
 	}
 
@@ -976,12 +980,12 @@ static int tcmu_configure_device(struct se_device *dev)
 	return ret;
 }
 
-static int tcmu_check_pending_cmd(int id, void *p, void *data)
+static int tcmu_check_and_free_pending_cmd(struct tcmu_cmd *cmd)
 {
-	struct tcmu_cmd *cmd = p;
-
-	if (test_bit(TCMU_CMD_BIT_EXPIRED, &cmd->flags))
+	if (test_bit(TCMU_CMD_BIT_EXPIRED, &cmd->flags)) {
+		kmem_cache_free(tcmu_cmd_cache, cmd);
 		return 0;
+	}
 	return -EINVAL;
 }
 
@@ -996,6 +1000,8 @@ static void tcmu_dev_call_rcu(struct rcu_head *p)
 static void tcmu_free_device(struct se_device *dev)
 {
 	struct tcmu_dev *udev = TCMU_DEV(dev);
+	struct tcmu_cmd *cmd;
+	bool all_expired = true;
 	int i;
 
 	del_timer_sync(&udev->timeout);
@@ -1004,10 +1010,13 @@ static void tcmu_free_device(struct se_device *dev)
 
 	/* Upper layer should drain all requests before calling this */
 	spin_lock_irq(&udev->commands_lock);
-	i = idr_for_each(&udev->commands, tcmu_check_pending_cmd, NULL);
+	idr_for_each_entry(&udev->commands, cmd, i) {
+		if (tcmu_check_and_free_pending_cmd(cmd) != 0)
+			all_expired = false;
+	}
 	idr_destroy(&udev->commands);
 	spin_unlock_irq(&udev->commands_lock);
-	WARN_ON(i);
+	WARN_ON(!all_expired);
 
 	/* Device was configured */
 	if (udev->uio_info.uio_dev) {