Patch "platform/x86: wmi: Fix opening of char device" has been added to the 5.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    platform/x86: wmi: Fix opening of char device

to the 5.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     platform-x86-wmi-fix-opening-of-char-device.patch
and it can be found in the queue-5.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 03e58bc7ac5352f4b75053dc60a1821124042dfc
Author: Armin Wolf <W_Armin@xxxxxx>
Date:   Fri Oct 20 23:10:04 2023 +0200

    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@xxxxxx>
    Link: https://lore.kernel.org/r/20231020211005.38216-5-W_Armin@xxxxxx
    Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>
    Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/platform/x86/wmi.c b/drivers/platform/x86/wmi.c
index a481707e0d398..66cfc35e4e3d0 100644
--- a/drivers/platform/x86/wmi.c
+++ b/drivers/platform/x86/wmi.c
@@ -817,21 +817,13 @@ 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);
 }