[PATCH] iommu/rockchip: check return value of of_find_device_by_node() in rk_iommu_of_xlate()

[PATCH] iommu/rockchip: check return value of of_find_device_by_node() in rk_iommu_of_xlate()

[Yu Kuai]

If of_find_device_by_node() failed in rk_iommu_of_xlate(), null pointer
dereference will be triggered. Thus return error code if
of_find_device_by_node() failed.

Fixes: 5fd577c3eac3("iommu/rockchip: Use OF_IOMMU to attach devices automatically")
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
 drivers/iommu/rockchip-iommu.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/iommu/rockchip-iommu.c b/drivers/iommu/rockchip-iommu.c
index e5d86b7177de..090d149ef8e9 100644
--- a/drivers/iommu/rockchip-iommu.c
+++ b/drivers/iommu/rockchip-iommu.c
@@ -1099,6 +1099,9 @@ static int rk_iommu_of_xlate(struct device *dev,
 
 	iommu_dev = of_find_device_by_node(args->np);
 
+	if (!iommu_dev)
+		return -ENODEV;
+
 	data->iommu = platform_get_drvdata(iommu_dev);
 	dev_iommu_priv_set(dev, data);
 
-- 
2.25.4

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Re: [PATCH] iommu/rockchip: check return value of of_find_device_by_node() in rk_iommu_of_xlate()

[Robin Murphy]

On 2020-10-29 09:22, Yu Kuai wrote:
> If of_find_device_by_node() failed in rk_iommu_of_xlate(), null pointer
> dereference will be triggered. Thus return error code if
> of_find_device_by_node() failed.

How can that happen? (Given that ".suppress_bind_attrs = true")

Robin.

> Fixes: 5fd577c3eac3("iommu/rockchip: Use OF_IOMMU to attach devices automatically")
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
> ---
>   drivers/iommu/rockchip-iommu.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/iommu/rockchip-iommu.c b/drivers/iommu/rockchip-iommu.c
> index e5d86b7177de..090d149ef8e9 100644
> --- a/drivers/iommu/rockchip-iommu.c
> +++ b/drivers/iommu/rockchip-iommu.c
> @@ -1099,6 +1099,9 @@ static int rk_iommu_of_xlate(struct device *dev,
>   
>   	iommu_dev = of_find_device_by_node(args->np);
>   
> +	if (!iommu_dev)
> +		return -ENODEV;
> +
>   	data->iommu = platform_get_drvdata(iommu_dev);
>   	dev_iommu_priv_set(dev, data);
>   
> 
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Re: [PATCH] iommu/rockchip: check return value of of_find_device_by_node() in rk_iommu_of_xlate()

[yukuai (C)]

On 2020/10/29 18:08, Robin Murphy wrote:
> On 2020-10-29 09:22, Yu Kuai wrote:
>> If of_find_device_by_node() failed in rk_iommu_of_xlate(), null pointer
>> dereference will be triggered. Thus return error code if
>> of_find_device_by_node() failed.
> 
> How can that happen? (Given that ".suppress_bind_attrs = true")
> 
> Robin.

I'm not sure if that could happen...

My thought is that it's better to do such checking to aviod any possible
problem.

Thanks!
Yu Kuai
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Re: [PATCH] iommu/rockchip: check return value of of_find_device_by_node() in rk_iommu_of_xlate()

[Robin Murphy]

On 2020-10-29 13:19, yukuai (C) wrote:
> 
> On 2020/10/29 18:08, Robin Murphy wrote:
>> On 2020-10-29 09:22, Yu Kuai wrote:
>>> If of_find_device_by_node() failed in rk_iommu_of_xlate(), null pointer
>>> dereference will be triggered. Thus return error code if
>>> of_find_device_by_node() failed.
>>
>> How can that happen? (Given that ".suppress_bind_attrs = true")
>>
>> Robin.
> 
> I'm not sure if that could happen...
> 
> My thought is that it's better to do such checking to aviod any possible
> problem.

->of_xlate() is only invoked on the specific set of ops returned by 
iommu_ops_from_fwnode(). In turn, iommu_ops_from_fwnode() will only 
return those ops if the driver has successfully probed and called 
iommu_register_device() with the relevant DT node. For the driver to 
have been able to probe at all, a platform device associated with that 
DT node must have been created, and therefore of_find_device_by_node() 
cannot fail.

If there ever were some problem serious enough to break that fundamental 
assumption, then I *want* these drivers to crash right here, with a nice 
clear stack trace to start debugging from. So no, I firmly disagree that 
adding redundant code, which will never do anything except attempt to 
paper over catastrophic memory corruption, is "better". Sorry :)

Robin.
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Re: [PATCH] iommu/rockchip: check return value of of_find_device_by_node() in rk_iommu_of_xlate()

[yukuai (C)]

On 2020/10/29 21:51, Robin Murphy wrote:
> On 2020-10-29 13:19, yukuai (C) wrote:
>>
>> On 2020/10/29 18:08, Robin Murphy wrote:
>>> On 2020-10-29 09:22, Yu Kuai wrote:
>>>> If of_find_device_by_node() failed in rk_iommu_of_xlate(), null pointer
>>>> dereference will be triggered. Thus return error code if
>>>> of_find_device_by_node() failed.
>>>
>>> How can that happen? (Given that ".suppress_bind_attrs = true")
>>>
>>> Robin.
>>
>> I'm not sure if that could happen...
>>
>> My thought is that it's better to do such checking to aviod any possible
>> problem.
> 
> ->of_xlate() is only invoked on the specific set of ops returned by 
> iommu_ops_from_fwnode(). In turn, iommu_ops_from_fwnode() will only 
> return those ops if the driver has successfully probed and called 
> iommu_register_device() with the relevant DT node. For the driver to 
> have been able to probe at all, a platform device associated with that 
> DT node must have been created, and therefore of_find_device_by_node() 
> cannot fail.
> 
> If there ever were some problem serious enough to break that fundamental 
> assumption, then I *want* these drivers to crash right here, with a nice 
> clear stack trace to start debugging from. So no, I firmly disagree that 
> adding redundant code, which will never do anything except attempt to 
> paper over catastrophic memory corruption, is "better". Sorry :)
> 

Sounds reasonable, thanks for your explanation

Yu Kuai
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