linux-kernel - Re: [PATCH] iommu/rockchip: Add missing check for of_find_device_by

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Date: Thu, 25 Apr 2024 11:35:53 +0100
From: Robin Murphy <robin.murphy@....com>
To: Chen Ni <nichen@...as.ac.cn>, joro@...tes.org, will@...nel.org,
 heiko@...ech.de, jeffy.chen@...k-chips.com
Cc: iommu@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
 linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iommu/rockchip: Add missing check for
 of_find_device_by_node

On 25/04/2024 10:18 am, Chen Ni wrote:
> Add check for the return value of of_find_device_by_node() and return
> the error if it fails in order to avoid NULL pointer dereference.

How would it return NULL?

Or to put it another way, if a device has somehow vanished without 
unbinding its driver or unregistering the iommu_ops through which this 
is called, then the kernel state is clearly so broken that crashing is 
probably the safest thing to do. Furthermore if we couldn't assume we 
have the right device here then we also couldn't assume that its drvdata 
points to the right thing either, so we'd be rather stuck.

Thanks,
Robin.

> Fixes: 5fd577c3eac3 ("iommu/rockchip: Use OF_IOMMU to attach devices automatically")
> Signed-off-by: Chen Ni <nichen@...as.ac.cn>
> ---
>   drivers/iommu/rockchip-iommu.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/iommu/rockchip-iommu.c b/drivers/iommu/rockchip-iommu.c
> index 4b369419b32c..1225c1df6ef6 100644
> --- a/drivers/iommu/rockchip-iommu.c
> +++ b/drivers/iommu/rockchip-iommu.c
> @@ -1152,6 +1152,8 @@ static int rk_iommu_of_xlate(struct device *dev,
>   		return -ENOMEM;
>   
>   	iommu_dev = of_find_device_by_node(args->np);
> +	if (!iommu_dev)
> +		return -ENODEV;
>   
>   	data->iommu = platform_get_drvdata(iommu_dev);
>   	data->iommu->domain = &rk_identity_domain;