[PATCH v3 1/2] rpmb: stop the routing after unregister

[Haruka Kuze]

From: Haruka Kuze <harukak@xxxxxxxxxxx>

OP-TEE has a reference of RPMB device it used. So, it can route
frames through the device after rpmb_dev_unregister() is called.
Therefore, the parent device passed to route_frames() can be
already freed, for example, mmc_blk_remove_rpmb_part() drops the
last reference after rpmb unregister.

This patch clears the route_frames when the device is going to
be removed by getting new rwsem and makes rpmb_route_frames()
return -ENODEV if the device is gone.

Fixes: 1e9046e3a154 ("rpmb: add Replay Protected Memory Block (RPMB) subsystem")
Assisted-by: LLM
Signed-off-by: Haruka Kuze <harukak@xxxxxxxxxxx>
---
 drivers/misc/rpmb-core.c | 14 +++++++++++++-
 include/linux/rpmb.h     |  4 ++++
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/drivers/misc/rpmb-core.c b/drivers/misc/rpmb-core.c
index ecf14acf230a..0ae018d1a276 100644
--- a/drivers/misc/rpmb-core.c
+++ b/drivers/misc/rpmb-core.c
@@ -45,7 +45,7 @@ EXPORT_SYMBOL_GPL(rpmb_dev_put);
  * @rsp:	rpmb response frames
  * @rsp_len:	length of rpmb response frames in bytes
  *
- * Returns: < 0 on failure
+ * Returns: < 0 on failure, -ENODEV if the device has been unregistered
  */
 int rpmb_route_frames(struct rpmb_dev *rdev, u8 *req,
 		      unsigned int req_len, u8 *rsp, unsigned int rsp_len)
@@ -53,6 +53,10 @@ int rpmb_route_frames(struct rpmb_dev *rdev, u8 *req,
 	if (!req || !req_len || !rsp || !rsp_len)
 		return -EINVAL;
 
+	guard(rwsem_read)(&rdev->lock);
+	if (!rdev->descr.route_frames)
+		return -ENODEV;
+
 	return rdev->descr.route_frames(rdev->dev.parent, req, req_len,
 					rsp, rsp_len);
 }
@@ -126,6 +130,10 @@ EXPORT_SYMBOL_GPL(rpmb_interface_unregister);
  * This function should be called from the release function of the
  * underlying device used when the RPMB device was registered.
  *
+ * Once this returns, rpmb_route_frames() no longer calls into
+ * the driver, even though the users might still hold a reference
+ * to the RPMB dev.
+ *
  * Returns: < 0 on failure
  */
 int rpmb_dev_unregister(struct rpmb_dev *rdev)
@@ -133,6 +141,9 @@ int rpmb_dev_unregister(struct rpmb_dev *rdev)
 	if (!rdev)
 		return -EINVAL;
 
+	scoped_guard(rwsem_write, &rdev->lock)
+		rdev->descr.route_frames = NULL;
+
 	device_del(&rdev->dev);
 
 	rpmb_dev_put(rdev);
@@ -165,6 +176,7 @@ struct rpmb_dev *rpmb_dev_register(struct device *dev,
 	if (!rdev)
 		return ERR_PTR(-ENOMEM);
 	rdev->descr = *descr;
+	init_rwsem(&rdev->lock);
 	rdev->descr.dev_id = kmemdup(descr->dev_id, descr->dev_id_len,
 				     GFP_KERNEL);
 	if (!rdev->descr.dev_id) {
diff --git a/include/linux/rpmb.h b/include/linux/rpmb.h
index ed3f8e431eff..0a976572d1cd 100644
--- a/include/linux/rpmb.h
+++ b/include/linux/rpmb.h
@@ -7,6 +7,7 @@
 #define __RPMB_H__
 
 #include <linux/device.h>
+#include <linux/rwsem.h>
 #include <linux/types.h>
 
 /**
@@ -51,12 +52,15 @@ struct rpmb_descr {
  * @id               : device_id
  * @list_node        : linked list node
  * @descr            : RPMB description
+ * @lock             : protect @descr.route_frames which is cleared when this
+ *                     device is unregistered
  */
 struct rpmb_dev {
 	struct device dev;
 	int id;
 	struct list_head list_node;
 	struct rpmb_descr descr;
+	struct rw_semaphore lock;
 };
 
 #define to_rpmb_dev(x)		container_of((x), struct rpmb_dev, dev)
-- 
2.55.0