linux-kernel - Re: [PATCH] iommu: Fix missing check for return value of iommu_group

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Date:   Thu, 15 Jun 2023 10:31:22 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Chenyuan Mi <cymi20@...an.edu.cn>, joro@...tes.org
Cc:     baolu.lu@...ux.intel.com, will@...nel.org, robin.murphy@....com,
        iommu@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu: Fix missing check for return value of
 iommu_group_get()

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@...an.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