nvme-fabrics: protect against module unload during create_ctrl

NVMe transport driver module unload may (and usually does) trigger
iteration over the active controllers and delete them all (sometimes
under a mutex).  However, a controller can be created concurrently with
module unload which can lead to leakage of resources (most important char
device node leakage) in case the controller creation occured after the
unload delete and drain sequence.  To protect against this, we take a
module reference to guarantee that the nvme transport driver is not
unloaded while creating a controller.

Signed-off-by: Roy Shterman <roys@lightbitslabs.com>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Max Gurtovoy <maxg@mellanox.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/host/fabrics.c

@@ -492,7 +492,7 @@ EXPORT_SYMBOL_GPL(nvmf_should_reconnect);
  */
 int nvmf_register_transport(struct nvmf_transport_ops *ops)
 {
-	if (!ops->create_ctrl)
+	if (!ops->create_ctrl || !ops->module)
 		return -EINVAL;
 
 	down_write(&nvmf_transports_rwsem);
@@ -868,32 +868,41 @@ nvmf_create_ctrl(struct device *dev, const char *buf, size_t count)
 		goto out_unlock;
 	}
 
+	if (!try_module_get(ops->module)) {
+		ret = -EBUSY;
+		goto out_unlock;
+	}
+
 	ret = nvmf_check_required_opts(opts, ops->required_opts);
 	if (ret)
-		goto out_unlock;
+		goto out_module_put;
 	ret = nvmf_check_allowed_opts(opts, NVMF_ALLOWED_OPTS |
 				ops->allowed_opts | ops->required_opts);
 	if (ret)
-		goto out_unlock;
+		goto out_module_put;
 
 	ctrl = ops->create_ctrl(dev, opts);
 	if (IS_ERR(ctrl)) {
 		ret = PTR_ERR(ctrl);
-		goto out_unlock;
+		goto out_module_put;
 	}
 
 	if (strcmp(ctrl->subsys->subnqn, opts->subsysnqn)) {
 		dev_warn(ctrl->device,
 			"controller returned incorrect NQN: \"%s\".\n",
 			ctrl->subsys->subnqn);
+		module_put(ops->module);
 		up_read(&nvmf_transports_rwsem);
 		nvme_delete_ctrl_sync(ctrl);
 		return ERR_PTR(-EINVAL);
 	}
 
+	module_put(ops->module);
 	up_read(&nvmf_transports_rwsem);
 	return ctrl;
 
+out_module_put:
+	module_put(ops->module);
 out_unlock:
 	up_read(&nvmf_transports_rwsem);
 out_free_opts:

drivers/nvme/host/fabrics.h

@@ -108,6 +108,7 @@ struct nvmf_ctrl_options {
  *			       fabric implementation of NVMe fabrics.
  * @entry:		Used by the fabrics library to add the new
  *			registration entry to its linked-list internal tree.
+ * @module:             Transport module reference
  * @name:		Name of the NVMe fabric driver implementation.
  * @required_opts:	sysfs command-line options that must be specified
  *			when adding a new NVMe controller.
@@ -126,6 +127,7 @@ struct nvmf_ctrl_options {
  */
 struct nvmf_transport_ops {
 	struct list_head	entry;
+	struct module		*module;
 	const char		*name;
 	int			required_opts;
 	int			allowed_opts;

drivers/nvme/host/fc.c

@@ -3381,6 +3381,7 @@ nvme_fc_create_ctrl(struct device *dev, struct nvmf_ctrl_options *opts)
 
 static struct nvmf_transport_ops nvme_fc_transport = {
 	.name		= "fc",
+	.module		= THIS_MODULE,
 	.required_opts	= NVMF_OPT_TRADDR | NVMF_OPT_HOST_TRADDR,
 	.allowed_opts	= NVMF_OPT_RECONNECT_DELAY | NVMF_OPT_CTRL_LOSS_TMO,
 	.create_ctrl	= nvme_fc_create_ctrl,

drivers/nvme/host/rdma.c

@@ -2006,6 +2006,7 @@ out_free_ctrl:
 
 static struct nvmf_transport_ops nvme_rdma_transport = {
 	.name		= "rdma",
+	.module		= THIS_MODULE,
 	.required_opts	= NVMF_OPT_TRADDR,
 	.allowed_opts	= NVMF_OPT_TRSVCID | NVMF_OPT_RECONNECT_DELAY |
 			  NVMF_OPT_HOST_TRADDR | NVMF_OPT_CTRL_LOSS_TMO,

drivers/nvme/target/loop.c

@@ -686,6 +686,7 @@ static struct nvmet_fabrics_ops nvme_loop_ops = {
 
 static struct nvmf_transport_ops nvme_loop_transport = {
 	.name		= "loop",
+	.module		= THIS_MODULE,
 	.create_ctrl	= nvme_loop_create_ctrl,
 };