Re: [PATCH] iommu: Fix missing check for return value of iommu_group_get()

[Baolu Lu <baolu.lu@linux.intel.com>]

On 6/14/23 11:43 PM, Chenyuan Mi wrote:
> The iommu_group_get() function may return NULL, which may
> cause null pointer deference, and most other callsites of
> iommu_group_get() do Null check. Add Null check for return
> value of iommu_group_get().
> 
> Found by our static analysis tool.
> 
> Signed-off-by: Chenyuan Mi <cymi20@fudan.edu.cn>
> ---
>   drivers/iommu/iommu.c | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index f1dcfa3f1a1b..ef3483e75511 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -3217,6 +3217,8 @@ EXPORT_SYMBOL_GPL(iommu_group_release_dma_owner);
>   void iommu_device_release_dma_owner(struct device *dev)
>   {
>   	struct iommu_group *group = iommu_group_get(dev);
> +	if (!group)
> +		return;

This interface should never be used in this way.

Check the comments of this function:

"Release the DMA ownership claimed by iommu_device_claim_dma_owner()."

iommu group has been checked in the claim api.

If any driver misuses this api, a null pointer deference warning is
better than ignoring silently.

>   
>   	mutex_lock(&group->mutex);
>   	if (group->owner_cnt > 1)
> @@ -3329,6 +3331,8 @@ void iommu_detach_device_pasid(struct iommu_domain *domain, struct device *dev,
>   			       ioasid_t pasid)
>   {
>   	struct iommu_group *group = iommu_group_get(dev);
> +	if (!group)
> +		return;

Ditto...

>   
>   	mutex_lock(&group->mutex);
>   	__iommu_remove_group_pasid(group, pasid);

Best regards,
baolu