Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <e8304083-931b-f52d-9865-8a79ba96c370@linux.intel.com>
Date:   Thu, 15 Jun 2023 10:31:22 +0800
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.11.0
Cc:     baolu.lu@linux.intel.com, will@kernel.org, robin.murphy@arm.com,
        iommu@lists.linux.dev, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] iommu: Fix missing check for return value of
 iommu_group_get()
Content-Language: en-US
To:     Chenyuan Mi <cymi20@fudan.edu.cn>, joro@8bytes.org
References: <20230614154308.118783-1-cymi20@fudan.edu.cn>
From:   Baolu Lu <baolu.lu@linux.intel.com>
In-Reply-To: <20230614154308.118783-1-cymi20@fudan.edu.cn>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

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