[PATCH 3/4] rpmsg: ctrl: Add check on rpmsg device removability from user space

[Arnaud Pouliquen <arnaud.pouliquen@xxxxxxxxxxx>]

Using the RPMSG_RELEASE_DEV_IOCTL is possible to remove any
rpmsg device (such as the rpmsg ns or the rpmsg ctrldev).

Add a new field to store the removability of the device.

By default the rpmsg device can not be removed by user space. It is
set to 1 by the rpmsg ctrl on RPMSG_CREATE_DEV_IOCTL request, but
could also be set by an rpmsg driver during probe.

Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@xxxxxxxxxxx>
---
 drivers/rpmsg/rpmsg_ctrl.c | 17 ++++++++++++++++-
 include/linux/rpmsg.h      |  2 ++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/drivers/rpmsg/rpmsg_ctrl.c b/drivers/rpmsg/rpmsg_ctrl.c
index cb19e32d05e1..e93c6ec49038 100644
--- a/drivers/rpmsg/rpmsg_ctrl.c
+++ b/drivers/rpmsg/rpmsg_ctrl.c
@@ -74,6 +74,7 @@ static long rpmsg_ctrldev_ioctl(struct file *fp, unsigned int cmd,
 	struct rpmsg_endpoint_info eptinfo;
 	struct rpmsg_channel_info chinfo;
 	struct rpmsg_device *rpdev;
+	struct device *dev;
 	int ret = 0;
 
 	if (copy_from_user(&eptinfo, argp, sizeof(eptinfo)))
@@ -95,11 +96,25 @@ static long rpmsg_ctrldev_ioctl(struct file *fp, unsigned int cmd,
 		if (!rpdev) {
 			dev_err(&ctrldev->dev, "failed to create %s channel\n", chinfo.name);
 			ret = -ENXIO;
+		} else {
+			/* Allow user space to release the device. */
+			rpdev->us_removable = 1;
 		}
 		break;
 
 	case RPMSG_RELEASE_DEV_IOCTL:
-		ret = rpmsg_release_channel(ctrldev->rpdev, &chinfo);
+		dev = rpmsg_find_device(ctrldev->rpdev->dev.parent, &chinfo);
+		if (!dev)
+			ret =  -ENXIO;
+
+		/* Verify that rpmsg device removal is allowed. */
+		if (!ret) {
+			rpdev = to_rpmsg_device(dev);
+			if (!rpdev->us_removable)
+				ret = -EACCES;
+		}
+		if (!ret)
+			ret = rpmsg_release_channel(ctrldev->rpdev, &chinfo);
 		if (ret)
 			dev_err(&ctrldev->dev, "failed to release %s channel (%d)\n",
 				chinfo.name, ret);
diff --git a/include/linux/rpmsg.h b/include/linux/rpmsg.h
index d97dcd049f18..3642aad1a789 100644
--- a/include/linux/rpmsg.h
+++ b/include/linux/rpmsg.h
@@ -47,6 +47,7 @@ struct rpmsg_channel_info {
  * @ept: the rpmsg endpoint of this channel
  * @announce: if set, rpmsg will announce the creation/removal of this channel
  * @little_endian: True if transport is using little endian byte representation
+ * @us_removable: True if userspace application has permission to remove the rpmsg device
  */
 struct rpmsg_device {
 	struct device dev;
@@ -57,6 +58,7 @@ struct rpmsg_device {
 	struct rpmsg_endpoint *ept;
 	bool announce;
 	bool little_endian;
+	bool us_removable;
 
 	const struct rpmsg_device_ops *ops;
 };
-- 
2.17.1