Re: [PATCH] iommu/arm-smmu: fix null-pointer dereference in arm_smmu_add_device

[Will Deacon]

Hi Artem,

Thanks for the patch.

On Tue, Aug 08, 2017 at 10:58:01AM +0200, Artem Savkov wrote:
> Commit c54451a "iommu/arm-smmu: Fix the error path in arm_smmu_add_device"
> removed fwspec assignment in legacy_binding path as redundant which is
> wrong. It needs to be updated after fwspec initialisation in
> arm_smmu_register_legacy_master() as it is dereferenced later. Without
> this there is a NULL-pointer dereference panic during boot on some hosts.
> 
> Signed-off-by: Artem Savkov 
> ---
>  drivers/iommu/arm-smmu.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> index b97188a..95f1c86 100644
> --- a/drivers/iommu/arm-smmu.c
> +++ b/drivers/iommu/arm-smmu.c
> @@ -1519,6 +1519,7 @@ static int arm_smmu_add_device(struct device *dev)
>  
>   if (using_legacy_binding) {
>   ret = arm_smmu_register_legacy_master(dev, );
> + fwspec = dev->iommu_fwspec;
>   if (ret)
>   goto out_free;
>   } else if (fwspec && fwspec->ops == _smmu_ops) {

Damn, you're completely right! Robin and I bashed our heads against this for
a while and couldn't remember why the code was structured like it was, but
that explains it. Can you add a comment saying that
arm_smmu_register_legacy_master will allocate an fwspec if its initially NULL,
please?

Cheers,

Will
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[PATCH] iommu/arm-smmu: fix null-pointer dereference in arm_smmu_add_device

[Artem Savkov]

Commit c54451a "iommu/arm-smmu: Fix the error path in arm_smmu_add_device"
removed fwspec assignment in legacy_binding path as redundant which is
wrong. It needs to be updated after fwspec initialisation in
arm_smmu_register_legacy_master() as it is dereferenced later. Without
this there is a NULL-pointer dereference panic during boot on some hosts.

Signed-off-by: Artem Savkov 
---
 drivers/iommu/arm-smmu.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
index b97188a..95f1c86 100644
--- a/drivers/iommu/arm-smmu.c
+++ b/drivers/iommu/arm-smmu.c
@@ -1519,6 +1519,7 @@ static int arm_smmu_add_device(struct device *dev)
 
if (using_legacy_binding) {
ret = arm_smmu_register_legacy_master(dev, );
+   fwspec = dev->iommu_fwspec;
if (ret)
goto out_free;
} else if (fwspec && fwspec->ops == _smmu_ops) {
-- 
2.7.5

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