[PATCH 5/6] platform/x86: wmi: Fix opening of char device

[Armin Wolf <W_Armin@gmx.de>]

Since commit fa1f68db6ca7 ("drivers: misc: pass miscdevice pointer via
file private data"), the miscdevice stores a pointer to itself inside
filp->private_data, which means that private_data will not be NULL when
wmi_char_open() is called. This might cause memory corruption should
wmi_char_open() be unable to find its driver, something which can happen
when the associated WMI device is deleted in wmi_free_devices().
Fix this by using the miscdevice pointer to retrieve the WMI device data
associated with a char device using container_of(). This also avoids
wmi_char_open() picking a wrong WMI device bound to a driver with the
same name as the original driver.

Fixes: 44b6b7661132 ("platform/x86: wmi: create userspace interface for drivers")
Signed-off-by: Armin Wolf <W_Armin@gmx.de>
---
 drivers/platform/x86/wmi.c | 20 ++++++--------------
 1 file changed, 6 insertions(+), 14 deletions(-)

diff --git a/drivers/platform/x86/wmi.c b/drivers/platform/x86/wmi.c
index ab24ea9ffc9a..6b3b2fe464d2 100644
--- a/drivers/platform/x86/wmi.c
+++ b/drivers/platform/x86/wmi.c
@@ -958,21 +958,13 @@ static int wmi_dev_match(struct device *dev, struct device_driver *driver)
 }
 static int wmi_char_open(struct inode *inode, struct file *filp)
 {
-	const char *driver_name = filp->f_path.dentry->d_iname;
-	struct wmi_block *wblock;
-	struct wmi_block *next;
-
-	list_for_each_entry_safe(wblock, next, &wmi_block_list, list) {
-		if (!wblock->dev.dev.driver)
-			continue;
-		if (strcmp(driver_name, wblock->dev.dev.driver->name) == 0) {
-			filp->private_data = wblock;
-			break;
-		}
-	}
+	/*
+	 * The miscdevice already stores a pointer to itself
+	 * inside filp->private_data
+	 */
+	struct wmi_block *wblock = container_of(filp->private_data, struct wmi_block, char_dev);

-	if (!filp->private_data)
-		return -ENODEV;
+	filp->private_data = wblock;

 	return nonseekable_open(inode, filp);
 }
--
2.39.2