Re: [PATCH] platform/x86: dell-wmi-sysman: fix a NULL pointer dereference
From: Perry Yuan
Date: Sun Jan 31 2021 - 21:40:32 EST
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@xxxxxxxxxx>
Sent: Saturday, January 30, 2021 15:44
To: Limonciello, Mario; Mark Gross
Cc: LKML; platform-driver-x86@xxxxxxxxxxxxxxx
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@xxxxxxxx>
---
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.