[PATCH] iommu: fix an incorrect NULL check on list iterator

[PATCH] iommu: fix an incorrect NULL check on list iterator

[Xiaomeng Tong]

The bug is here:
	if (!iommu || iommu->dev->of_node != spec->np) {

The list iterator value 'iommu' will *always* be set and non-NULL by
list_for_each_entry(), so it is incorrect to assume that the iterator
value will be NULL if the list is empty or no element is found (in fact,
it will point to a invalid structure object containing HEAD).

To fix the bug, run insert_iommu_master(dev, &iommu, spec); unlock and
return 0 when found, otherwise unlock and return -ENODEV.

Cc: stable@vger.kernel.org
Fixes: f78ebca8ff3d6 ("iommu/msm: Add support for generic master bindings")
Signed-off-by: Xiaomeng Tong <xiam0nd.tong@gmail.com>
---
 drivers/iommu/msm_iommu.c | 18 ++++++------------
 1 file changed, 6 insertions(+), 12 deletions(-)

diff --git a/drivers/iommu/msm_iommu.c b/drivers/iommu/msm_iommu.c
index 3a38352b603f..1dbb8b0695ec 100644
--- a/drivers/iommu/msm_iommu.c
+++ b/drivers/iommu/msm_iommu.c
@@ -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;
 }
 
 irqreturn_t msm_iommu_fault_handler(int irq, void *dev_id)
-- 
2.17.1

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

[Joerg Roedel]

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