linux-kernel - Re: [PATCH] platform/x86: dell-wmi-sysman: fix a NULL pointer dereference

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Date:   Sat, 30 Jan 2021 22:43:42 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Mario Limonciello <mario.limonciello@...l.com>,
        Mark Gross <mgross@...ux.intel.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        platform-driver-x86@...r.kernel.org
Subject: Re: [PATCH] platform/x86: dell-wmi-sysman: fix a NULL pointer
 dereference

Hi,

On 1/29/21 6:26 PM, Mario Limonciello wrote:
> An upcoming Dell platform is causing a NULL pointer dereference
> in dell-wmi-sysman initialization.  Validate that the input from
> BIOS matches correct ACPI types and abort module initialization
> if it fails.
> 
> This leads to a memory leak that needs to be cleaned up properly.
> 
> Signed-off-by: Mario Limonciello <mario.limonciello@...l.com>
> ---
>  drivers/platform/x86/dell-wmi-sysman/sysman.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/platform/x86/dell-wmi-sysman/sysman.c b/drivers/platform/x86/dell-wmi-sysman/sysman.c
> index dc6dd531c996..38b497991071 100644
> --- a/drivers/platform/x86/dell-wmi-sysman/sysman.c
> +++ b/drivers/platform/x86/dell-wmi-sysman/sysman.c
> @@ -419,13 +419,19 @@ static int init_bios_attributes(int attr_type, const char *guid)
>  		return retval;
>  	/* need to use specific instance_id and guid combination to get right data */
>  	obj = get_wmiobj_pointer(instance_id, guid);
> -	if (!obj)
> +	if (!obj || obj->type != ACPI_TYPE_PACKAGE) {
> +		release_attributes_data();

All calls of  init_bios_attributes() have the following error handling:

        ret = init_bios_attributes(INT, DELL_WMI_BIOS_INTEGER_ATTRIBUTE_GUID);
        if (ret) {
                pr_debug("failed to populate integer type attributes\n");
                goto fail_create_group;
        }

	...

fail_create_group:
        release_attributes_data();

So that added release_attributes_data() call is not necessary. If you can respin
this patch Monday with the release_attributes_data(); addition dropped, then
I will try to get this to Linus in time for 5.11 .

Or I can fix this up locally if you agree with dropping the unnecessary
release_attributes_data() call.

Regards,

Hans




>  		return -ENODEV;
> +	}
>  	elements = obj->package.elements;
>  
>  	mutex_lock(&wmi_priv.mutex);
>  	while (elements) {
>  		/* sanity checking */
> +		if (elements[ATTR_NAME].type != ACPI_TYPE_STRING) {
> +			pr_debug("incorrect element type\n");
> +			goto nextobj;
> +		}
>  		if (strlen(elements[ATTR_NAME].string.pointer) == 0) {
>  			pr_debug("empty attribute found\n");
>  			goto nextobj;
>