Re: [PATCH] iommu: Fix refcount leak in iommu_device_claim_dma_owner

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

On 12/30/22 4:31 PM, Miaoqian Lin wrote:
> iommu_group_get() returns the group with the reference incremented.
> Move iommu_group_get() after owner check to fix the refcount leak.

An empty @owner is a more serious problem than refcount leak. It should
not happen, so a WARN_ON() was added there.

Anyway, your change makes the code better.

> 
> Fixes: 89395ccedbc1 ("iommu: Add device-centric DMA ownership interfaces")
> Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
> ---
>   drivers/iommu/iommu.c | 8 +++++---
>   1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index de91dd88705b..3a7dd8b61fab 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -3185,14 +3185,16 @@ EXPORT_SYMBOL_GPL(iommu_group_claim_dma_owner);
>    */
>   int iommu_device_claim_dma_owner(struct device *dev, void *owner)
>   {
> -	struct iommu_group *group = iommu_group_get(dev);
> +	struct iommu_group *group = NULL;

No need to set NULL to group.

>   	int ret = 0;
>   
> -	if (!group)
> -		return -ENODEV;
>   	if (WARN_ON(!owner))
>   		return -EINVAL;
>   
> +	group = iommu_group_get(dev);
> +	if (!group)
> +		return -ENODEV;
> +
>   	mutex_lock(&group->mutex);
>   	if (group->owner_cnt) {
>   		if (group->owner != owner) {

Others look good to me.

Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>

--
Best regards,
baolu