[PATCH v2] nvme-fabrics: Protect against module unload during create_ctrl

[Sagi Grimberg]

From: Roy Shterman <roys at lightbitslabs.com>

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 at lightbitslabs.com>
Signed-off-by: Sagi Grimberg <sagi at grimberg.me>
---
Changes from v1:
- restored missing module ref put is success flow

 drivers/nvme/host/fabrics.c | 17 +++++++++++++----
 drivers/nvme/host/fabrics.h |  2 ++
 drivers/nvme/host/fc.c      |  1 +
 drivers/nvme/host/rdma.c    |  1 +
 drivers/nvme/target/loop.c  |  1 +
 5 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/drivers/nvme/host/fabrics.c b/drivers/nvme/host/fabrics.c
index 76b4fe6816a0..2f68befd31bf 100644
--- a/drivers/nvme/host/fabrics.c
+++ b/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:
diff --git a/drivers/nvme/host/fabrics.h b/drivers/nvme/host/fabrics.h
index 9ba614953607..25b19f722f5b 100644
--- a/drivers/nvme/host/fabrics.h
+++ b/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;
diff --git a/drivers/nvme/host/fc.c b/drivers/nvme/host/fc.c
index e2ade0237ffe..e68c6b84c177 100644
--- a/drivers/nvme/host/fc.c
+++ b/drivers/nvme/host/fc.c
@@ -3380,6 +3380,7 @@ 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,
diff --git a/drivers/nvme/host/rdma.c b/drivers/nvme/host/rdma.c
index 62188c41763b..a5ad1fbd9488 100644
--- a/drivers/nvme/host/rdma.c
+++ b/drivers/nvme/host/rdma.c
@@ -2006,6 +2006,7 @@ static struct nvme_ctrl *nvme_rdma_create_ctrl(struct device *dev,
 
 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,
diff --git a/drivers/nvme/target/loop.c b/drivers/nvme/target/loop.c
index e83fc562612a..8fe0edd0b421 100644
--- a/drivers/nvme/target/loop.c
+++ b/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,
 };
 
-- 
2.14.1