linux-kernel - Re: [PATCH] iommu: fix an incorrect NULL check on list iterator

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Date:   Thu, 28 Apr 2022 10:11:03 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Xiaomeng Tong <xiam0nd.tong@...il.com>
Cc:     agross@...nel.org, bjorn.andersson@...aro.org, will@...nel.org,
        sricharan@...eaurora.org, linux-arm-msm@...r.kernel.org,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH] iommu: fix an incorrect NULL check on list iterator

On Sun, Mar 27, 2022 at 01:35:58PM +0800, Xiaomeng Tong wrote:
> @@ -617,23 +617,17 @@ static int qcom_iommu_of_xlate(struct device *dev,
>  {
>  	struct msm_iommu_dev *iommu;
>  	unsigned long flags;
> -	int ret = 0;
>  
>  	spin_lock_irqsave(&msm_iommu_lock, flags);
>  	list_for_each_entry(iommu, &qcom_iommu_devices, dev_node)
> -		if (iommu->dev->of_node == spec->np)
> -			break;
> -
> -	if (!iommu || iommu->dev->of_node != spec->np) {
> -		ret = -ENODEV;
> -		goto fail;
> -	}
> -
> -	insert_iommu_master(dev, &iommu, spec);
> -fail:
> +		if (iommu->dev->of_node == spec->np) {
> +			insert_iommu_master(dev, &iommu, spec);
> +			spin_unlock_irqrestore(&msm_iommu_lock, flags);
> +			return 0;
> +		}
>  	spin_unlock_irqrestore(&msm_iommu_lock, flags);
>  
> -	return ret;
> +	return -ENODEV;

This looks a bit clumsy, a better fix is below:

diff --git a/drivers/iommu/msm_iommu.c b/drivers/iommu/msm_iommu.c
index 50f57624610f..98d23c52537b 100644
--- a/drivers/iommu/msm_iommu.c
+++ b/drivers/iommu/msm_iommu.c
@@ -610,14 +610,16 @@ static void insert_iommu_master(struct device *dev,
 static int qcom_iommu_of_xlate(struct device *dev,
 			       struct of_phandle_args *spec)
 {
-	struct msm_iommu_dev *iommu;
+	struct msm_iommu_dev *iommu = NULL, *it;
 	unsigned long flags;
 	int ret = 0;
 
 	spin_lock_irqsave(&msm_iommu_lock, flags);
-	list_for_each_entry(iommu, &qcom_iommu_devices, dev_node)
-		if (iommu->dev->of_node == spec->np)
+	list_for_each_entry(it, &qcom_iommu_devices, dev_node)
+		if (it->dev->of_node == spec->np) {
+			iommu = it;
 			break;
+		}
 
 	if (!iommu || iommu->dev->of_node != spec->np) {
 		ret = -ENODEV;

Can you please verify this and re-submit?

Thanks,

	Joerg