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[PATCH] intel_menlow: set cdev after null device check to avoid null pointer dereference

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  [PATCH] intel_menlow: set cdev after null device check to avoid null pointer dereference Colin King <colin.king@canonical.com> - 2016-03-28 18:20 +0200
    Re: [PATCH] intel_menlow: set cdev after null device check to avoid  null pointer dereference Darren Hart <dvhart@infradead.org> - 2016-03-28 20:30 +0200
      Re: [PATCH] intel_menlow: set cdev after null device check to avoid null pointer dereference "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-03-29 15:20 +0200

#1365567 — [PATCH] intel_menlow: set cdev after null device check to avoid null pointer dereference

From: Colin Ian King <colin.king@canonical.com>

intel_menlow_memory_remove sanity checks to see if device is null, however,
this check is performed after we have already passed device into a call
to acpi_driver_data.  If device is null, then acpi_driver_data will produce
a null pointer dereference on device. The correct action is to sanity check
device, then assign cdev, then check if cdev is null.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
---
 drivers/platform/x86/intel_menlow.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/platform/x86/intel_menlow.c b/drivers/platform/x86/intel_menlow.c
index 0a919d8..185a1bd 100644
--- a/drivers/platform/x86/intel_menlow.c
+++ b/drivers/platform/x86/intel_menlow.c
@@ -196,9 +196,13 @@ static int intel_menlow_memory_add(struct acpi_device *device)
 
 static int intel_menlow_memory_remove(struct acpi_device *device)
 {
-	struct thermal_cooling_device *cdev = acpi_driver_data(device);
+	struct thermal_cooling_device *cdev;
+
+	if (!device)
+		return -EINVAL;
 
-	if (!device || !cdev)
+	cdev = acpi_driver_data(device);
+	if (!cdev)
 		return -EINVAL;
 
 	sysfs_remove_link(&device->dev.kobj, "thermal_cooling");
-- 
2.7.4

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#1365626 — Re: [PATCH] intel_menlow: set cdev after null device check to avoid null pointer dereference

On Mon, Mar 28, 2016 at 05:18:39PM +0100, Colin King wrote:
> From: Colin Ian King <colin.king@canonical.com>
> 
> intel_menlow_memory_remove sanity checks to see if device is null, however,
> this check is performed after we have already passed device into a call
> to acpi_driver_data.  If device is null, then acpi_driver_data will produce
> a null pointer dereference on device. The correct action is to sanity check
> device, then assign cdev, then check if cdev is null.
> 

Hrm, looking at this locally, that all makes sense.

Taking a step back however, I notice that intel_menlow_memory_remove is an ops
function pointer inside the acpi_driver structure itself, which is called from
acpi_device_remove() (and probe) (drivers/acpi/bus.c). This already verifies
acpi_driver is not NULL and can't get acpi_driver if acpi_device is NULL. So
unless there is some other use case for this callback I'm unaware of (certainly
possible) it appears to be totally redundant to do this checking here.

+Rafael - is there a best practices for these acpi callbacks with respect to
input validation?

> Signed-off-by: Colin Ian King <colin.king@canonical.com>
> ---
>  drivers/platform/x86/intel_menlow.c | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/platform/x86/intel_menlow.c b/drivers/platform/x86/intel_menlow.c
> index 0a919d8..185a1bd 100644
> --- a/drivers/platform/x86/intel_menlow.c
> +++ b/drivers/platform/x86/intel_menlow.c
> @@ -196,9 +196,13 @@ static int intel_menlow_memory_add(struct acpi_device *device)
>  
>  static int intel_menlow_memory_remove(struct acpi_device *device)
>  {
> -	struct thermal_cooling_device *cdev = acpi_driver_data(device);
> +	struct thermal_cooling_device *cdev;
> +
> +	if (!device)
> +		return -EINVAL;
>  
> -	if (!device || !cdev)
> +	cdev = acpi_driver_data(device);
> +	if (!cdev)
>  		return -EINVAL;
>  
>  	sysfs_remove_link(&device->dev.kobj, "thermal_cooling");
> -- 
> 2.7.4
> 
> 

-- 
Darren Hart
Intel Open Source Technology Center

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#1366282

On Monday, March 28, 2016 11:18:05 AM Darren Hart wrote:
> On Mon, Mar 28, 2016 at 05:18:39PM +0100, Colin King wrote:
> > From: Colin Ian King <colin.king@canonical.com>
> > 
> > intel_menlow_memory_remove sanity checks to see if device is null, however,
> > this check is performed after we have already passed device into a call
> > to acpi_driver_data.  If device is null, then acpi_driver_data will produce
> > a null pointer dereference on device. The correct action is to sanity check
> > device, then assign cdev, then check if cdev is null.
> > 
> 
> Hrm, looking at this locally, that all makes sense.
> 
> Taking a step back however, I notice that intel_menlow_memory_remove is an ops
> function pointer inside the acpi_driver structure itself, which is called from
> acpi_device_remove() (and probe) (drivers/acpi/bus.c). This already verifies
> acpi_driver is not NULL and can't get acpi_driver if acpi_device is NULL. So
> unless there is some other use case for this callback I'm unaware of (certainly
> possible) it appears to be totally redundant to do this checking here.
> 
> +Rafael - is there a best practices for these acpi callbacks with respect to
> input validation?

No best practices I'm aware of, but if the core does this checks anyway before
calling this, they are clearly not necessary here.

Thanks,
Rafael

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