2022-03-28 19:51:03

by Xiaomeng Tong

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

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: [email protected]
Fixes: f78ebca8ff3d6 ("iommu/msm: Add support for generic master bindings")
Signed-off-by: Xiaomeng Tong <[email protected]>
---
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

2022-04-28 09:20:36

by Joerg Roedel

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