platform/x86: wmi: Fix opening of char device

[ Upstream commit eba9ac7abab91c8f6d351460239108bef5e7a0b6 ]

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 the problem 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>
Link: https://lore.kernel.org/r/20231020211005.38216-5-W_Armin@gmx.de
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/platform/x86/wmi.c b/drivers/platform/x86/wmi.c
index 0fcfdc5..2b79377 100644 (file)
--- a/drivers/platform/x86/wmi.c
+++ b/drivers/platform/x86/wmi.c
@@ -849,21 +849,13 @@ 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);
 }