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Date: Mon, 1 Feb 2021 10:36:21 +0800
From: Perry Yuan <perry979106@...il.com>
To: Hans de Goede <hdegoede@...hat.com>,
"Limonciello, Mario" <Mario.Limonciello@...l.com>,
Mark Gross <mgross@...ux.intel.com>
Cc: LKML <linux-kernel@...r.kernel.org>,
"platform-driver-x86@...r.kernel.org"
<platform-driver-x86@...r.kernel.org>
Subject: Re: [PATCH] platform/x86: dell-wmi-sysman: fix a NULL pointer
dereference
On 2021/2/1 4:59, Hans de Goede wrote:
> Hi,
>
> On 1/31/21 3:04 PM, Limonciello, Mario wrote:
>>
>>
>>> -----Original Message-----
>>> From: Hans de Goede <hdegoede@...hat.com>
>>> Sent: Saturday, January 30, 2021 15:44
>>> To: Limonciello, Mario; Mark Gross
>>> Cc: LKML; platform-driver-x86@...r.kernel.org
>>> Subject: Re: [PATCH] platform/x86: dell-wmi-sysman: fix a NULL pointer
>>> dereference
>>>
>>>
>>> [EXTERNAL EMAIL]
>>>
>>> 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.
>>>
>>
>> Yes, please go ahead and drop the unnecessary call locally.
>
> Ok, I've merged this into my review-hans branch and I will push this out
> to for-next as soon as a local build has finished. I'll also include
> this in my last fixes pull-req for Linus later this week.
>
> While working on this I did notice that the function in question still
> has a bunch of further issues. But since this patch fixes a crash and has
> been tested I've decided to move forward with it as is (with the duplicate
> release_attributes_data() call dropped). The further issues can be fixed
> with follow-up patches.
>
> So the other issues which I noticed are:
>
> 1. Calling release_attributes_data() in the error-path here:
>
> obj = get_wmiobj_pointer(instance_id, guid);
> if (!obj || obj->type != ACPI_TYPE_PACKAGE) {
> return -ENODEV;
> }
>
> Is not necessary as discussed, but the added obj->type != ACPI_TYPE_PACKAGE
> which I assume triggers to fix the reported crash, means that obj is not
> NULL in which case we should free it. So this should become:
>
> obj = get_wmiobj_pointer(instance_id, guid);
> if (!obj || obj->type != ACPI_TYPE_PACKAGE) {
> kfree(obj);
> return -ENODEV;
> }
>
> Note that the kfree() will be a no-op when obj == NULL. This means that
> with just the current fix merged there is a small memleak on machines
> where we hit the error-path. I've decided that we can live with that,
> since the alternative is the crash or me pushing something untested.
>
>
> 2. There is a while below this if, which gets a new obj pointer:
>
> obj = get_wmiobj_pointer(instance_id, guid);
> if (!obj || obj->type != ACPI_TYPE_PACKAGE) {
> kfree(obj);
> return -ENODEV;
> }
> elements = obj->package.elements;
>
> mutex_lock(&wmi_priv.mutex);
> while (elements) {
> ...
>
> nextobj:
> kfree(obj);
> instance_id++;
> obj = get_wmiobj_pointer(instance_id, guid);
> elements = obj ? obj->package.elements : NULL;
> }
>
> This is missing a check for the obj->type for the new obj when
> going into a second (or higher) iteration of the loop.
>
> This check can be added by moving the original check to inside
> the loop like this:
>
> obj = get_wmiobj_pointer(instance_id, guid);
>
> mutex_lock(&wmi_priv.mutex);
> while (obj) {
> if (obj->type != ACPI_TYPE_PACKAGE) {
> err = ENODEV;
> goto err_attr_init;
> }
> elements = obj->package.elements;
>
> ...
>
> nextobj:
> kfree(obj);
> instance_id++;
> obj = get_wmiobj_pointer(instance_id, guid);
> }
>
>
> 3. Functions like populate_enum_data() (and the others) index the
> elements array with an index > 0 without checking the package length
> and also make assumptions about the types embedded in the package
> without checking them.
>
>
> 4. The err_attr_init exit path of init_bios_attributes() calls
> release_attributes_data() but that call does not just cleanup
> the results of that single init_bios_attributes() call but also
> of all previous init_bios_attributes() calls as such it makes more
> sense to leave the calling of release_attributes_data() to the caller.
>
> Either way calling it twice once from the err_attr_init exit path
> and then again in sysman_init() feels wrong, even though I think it
> does no harm.
>
> Regards,
>
> Hans
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>>
>> Thank you
>>
>>> 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;
>>>>
>>
>
Hi Hans.
Could you share your the commit link after you apply this patch to your
for-next branch?
Thank you!
Perry.
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