nvmet: model_number must be immutable once set

In case we have already established connection to nvmf target, it
shouldn't be allowed to change the model_number. E.g. if someone will
identify ctrl and get model_number of "my_model" later on will change
the model_numbel via configfs to "my_new_model" this will break the NVMe
specification for "Get Log Page – Persistent Event Log" that refers to
Model Number as: "This field contains the same value as reported in the
Model Number field of the Identify Controller data structure, bytes
63:24."

Although it doesn't mentioned explicitly that this field can't be
changed, we can assume it.

So allow setting this field only once: using configfs or in the first
identify ctrl operation.
Signed-off-by: Max Gurtovoy <mgurtovoy@nvidia.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/target/admin-cmd.c

@@ -313,27 +313,40 @@ static void nvmet_execute_get_log_page(struct nvmet_req *req)
 	nvmet_req_complete(req, NVME_SC_INVALID_FIELD | NVME_SC_DNR);
 }
 
-static void nvmet_id_set_model_number(struct nvme_id_ctrl *id,
-				      struct nvmet_subsys *subsys)
+static u16 nvmet_set_model_number(struct nvmet_subsys *subsys)
 {
-	const char *model = NVMET_DEFAULT_CTRL_MODEL;
-	struct nvmet_subsys_model *subsys_model;
+	u16 status = 0;
 
-	rcu_read_lock();
-	subsys_model = rcu_dereference(subsys->model);
-	if (subsys_model)
-		model = subsys_model->number;
-	memcpy_and_pad(id->mn, sizeof(id->mn), model, strlen(model), ' ');
-	rcu_read_unlock();
+	mutex_lock(&subsys->lock);
+	if (!subsys->model_number) {
+		subsys->model_number =
+			kstrdup(NVMET_DEFAULT_CTRL_MODEL, GFP_KERNEL);
+		if (!subsys->model_number)
+			status = NVME_SC_INTERNAL;
+	}
+	mutex_unlock(&subsys->lock);
+
+	return status;
 }
 
 static void nvmet_execute_identify_ctrl(struct nvmet_req *req)
 {
 	struct nvmet_ctrl *ctrl = req->sq->ctrl;
+	struct nvmet_subsys *subsys = ctrl->subsys;
 	struct nvme_id_ctrl *id;
 	u32 cmd_capsule_size;
 	u16 status = 0;
 
+	/*
+	 * If there is no model number yet, set it now.  It will then remain
+	 * stable for the life time of the subsystem.
+	 */
+	if (!subsys->model_number) {
+		status = nvmet_set_model_number(subsys);
+		if (status)
+			goto out;
+	}
+
 	id = kzalloc(sizeof(*id), GFP_KERNEL);
 	if (!id) {
 		status = NVME_SC_INTERNAL;
@@ -347,7 +360,8 @@ static void nvmet_execute_identify_ctrl(struct nvmet_req *req)
 	memset(id->sn, ' ', sizeof(id->sn));
 	bin2hex(id->sn, &ctrl->subsys->serial,
 		min(sizeof(ctrl->subsys->serial), sizeof(id->sn) / 2));
-	nvmet_id_set_model_number(id, ctrl->subsys);
+	memcpy_and_pad(id->mn, sizeof(id->mn), subsys->model_number,
+		       strlen(subsys->model_number), ' ');
 	memcpy_and_pad(id->fr, sizeof(id->fr),
 		       UTS_RELEASE, strlen(UTS_RELEASE), ' ');
 

drivers/nvme/target/configfs.c

@@ -1118,16 +1118,12 @@ static ssize_t nvmet_subsys_attr_model_show(struct config_item *item,
 					    char *page)
 {
 	struct nvmet_subsys *subsys = to_subsys(item);
-	struct nvmet_subsys_model *subsys_model;
-	char *model = NVMET_DEFAULT_CTRL_MODEL;
 	int ret;
 
-	rcu_read_lock();
-	subsys_model = rcu_dereference(subsys->model);
-	if (subsys_model)
-		model = subsys_model->number;
-	ret = snprintf(page, PAGE_SIZE, "%s\n", model);
-	rcu_read_unlock();
+	mutex_lock(&subsys->lock);
+	ret = snprintf(page, PAGE_SIZE, "%s\n", subsys->model_number ?
+			subsys->model_number : NVMET_DEFAULT_CTRL_MODEL);
+	mutex_unlock(&subsys->lock);
 
 	return ret;
 }
@@ -1138,14 +1134,17 @@ static bool nvmet_is_ascii(const char c)
 	return c >= 0x20 && c <= 0x7e;
 }
 
-static ssize_t nvmet_subsys_attr_model_store(struct config_item *item,
+static ssize_t nvmet_subsys_attr_model_store_locked(struct nvmet_subsys *subsys,
 		const char *page, size_t count)
 {
-	struct nvmet_subsys *subsys = to_subsys(item);
-	struct nvmet_subsys_model *new_model;
-	char *new_model_number;
 	int pos = 0, len;
 
+	if (subsys->model_number) {
+		pr_err("Can't set model number. %s is already assigned\n",
+		       subsys->model_number);
+		return -EINVAL;
+	}
+
 	len = strcspn(page, "\n");
 	if (!len)
 		return -EINVAL;
@@ -1155,28 +1154,25 @@ static ssize_t nvmet_subsys_attr_model_store(struct config_item *item,
 			return -EINVAL;
 	}
 
-	new_model_number = kmemdup_nul(page, len, GFP_KERNEL);
-	if (!new_model_number)
+	subsys->model_number = kmemdup_nul(page, len, GFP_KERNEL);
+	if (!subsys->model_number)
 		return -ENOMEM;
+	return count;
+}
 
-	new_model = kzalloc(sizeof(*new_model) + len + 1, GFP_KERNEL);
-	if (!new_model) {
-		kfree(new_model_number);
-		return -ENOMEM;
-	}
-	memcpy(new_model->number, new_model_number, len);
+static ssize_t nvmet_subsys_attr_model_store(struct config_item *item,
+					     const char *page, size_t count)
+{
+	struct nvmet_subsys *subsys = to_subsys(item);
+	ssize_t ret;
 
 	down_write(&nvmet_config_sem);
 	mutex_lock(&subsys->lock);
-	new_model = rcu_replace_pointer(subsys->model, new_model,
-					mutex_is_locked(&subsys->lock));
+	ret = nvmet_subsys_attr_model_store_locked(subsys, page, count);
 	mutex_unlock(&subsys->lock);
 	up_write(&nvmet_config_sem);
 
-	kfree_rcu(new_model, rcuhead);
-	kfree(new_model_number);
-
-	return count;
+	return ret;
 }
 CONFIGFS_ATTR(nvmet_subsys_, attr_model);
 

drivers/nvme/target/core.c

@@ -1532,7 +1532,7 @@ static void nvmet_subsys_free(struct kref *ref)
 	nvmet_passthru_subsys_free(subsys);
 
 	kfree(subsys->subsysnqn);
-	kfree_rcu(subsys->model, rcuhead);
+	kfree(subsys->model_number);
 	kfree(subsys);
 }
 

drivers/nvme/target/nvmet.h

@@ -208,11 +208,6 @@ struct nvmet_ctrl {
 	bool			pi_support;
 };
 
-struct nvmet_subsys_model {
-	struct rcu_head		rcuhead;
-	char			number[];
-};
-
 struct nvmet_subsys {
 	enum nvme_subsys_type	type;
 
@@ -242,7 +237,7 @@ struct nvmet_subsys {
 	struct config_group	namespaces_group;
 	struct config_group	allowed_hosts_group;
 
-	struct nvmet_subsys_model	__rcu *model;
+	char			*model_number;
 
 #ifdef CONFIG_NVME_TARGET_PASSTHRU
 	struct nvme_ctrl	*passthru_ctrl;