linux-kernel - Re: [PATCH] dma-direct: Fix potential NULL pointer dereference

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Date:   Tue, 15 Sep 2020 17:09:29 +0200
From:   Christoph Hellwig <hch@....de>
To:     Thomas Tai <thomas.tai@...cle.com>
Cc:     Christoph Hellwig <hch@....de>, konrad.wilk@...cle.com,
        m.szyprowski@...sung.com, robin.murphy@....com,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dma-direct: Fix potential NULL pointer dereference

On Tue, Sep 15, 2020 at 10:40:39AM -0400, Thomas Tai wrote:
>> +++ b/include/linux/dma-direct.h
>> @@ -62,9 +62,6 @@ static inline bool dma_capable(struct device *dev, dma_addr_t addr, size_t size,
>>   {
>>   	dma_addr_t end = addr + size - 1;
>>   -	if (!dev->dma_mask)
>> -		return false;
>> -
>
> I am concerned that some drivers may rely on this NULL checking. Would you 
> think we can keep this checking and use the following WARN_ON_ONCE()?

dma_capable is not a helper for drivers, but just for dma-direct
and related code.  And this patch adds the checks for the three
places how we call into the ->map* methods.