[PATCH 1/1] misc: Prevent double registration and deregistration of miscdevice

[<xion.wang@mediatek.com>]

From: Xion Wang <xion.wang@mediatek.com>

When repeated calls to misc_register() or misc_deregister() on the
same miscdevice could lead to kernel crashes or misc_list corruption due to
multiple INIT_LIST_HEAD or list_del operations on the same list node.

This patch improves the robustness of the misc device driver by preventing
both double registration and double deregistration of miscdevice instances.

Signed-off-by: Xion Wang <xion.wang@mediatek.com>
---
 drivers/char/misc.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/char/misc.c b/drivers/char/misc.c
index 558302a64dd9..2f8666312966 100644
--- a/drivers/char/misc.c
+++ b/drivers/char/misc.c
@@ -210,6 +210,9 @@ int misc_register(struct miscdevice *misc)
 	int err = 0;
 	bool is_dynamic = (misc->minor == MISC_DYNAMIC_MINOR);
 
+	if (WARN_ON(misc->this_device))
+		return -EEXIST;
+
 	INIT_LIST_HEAD(&misc->list);
 
 	mutex_lock(&misc_mtx);
@@ -251,6 +254,7 @@ int misc_register(struct miscdevice *misc)
 			misc->minor = MISC_DYNAMIC_MINOR;
 		}
 		err = PTR_ERR(misc->this_device);
+		misc->this_device = NULL;
 		goto out;
 	}
 
@@ -275,12 +279,13 @@ EXPORT_SYMBOL(misc_register);
 
 void misc_deregister(struct miscdevice *misc)
 {
-	if (WARN_ON(list_empty(&misc->list)))
+	if (WARN_ON(!misc->this_device))
 		return;
 
 	mutex_lock(&misc_mtx);
 	list_del(&misc->list);
 	device_destroy(&misc_class, MKDEV(MISC_MAJOR, misc->minor));
+	misc->this_device = NULL;
 	misc_minor_free(misc->minor);
 	mutex_unlock(&misc_mtx);
 }
-- 
2.45.2