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

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Message-ID: <9a819530-365b-9982-c9c9-ad20d6c8149e@oracle.com>
Date:   Tue, 15 Sep 2020 11:12:28 -0400
From:   Thomas Tai <thomas.tai@...cle.com>
To:     Christoph Hellwig <hch@....de>
Cc:     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 2020-09-15 11:09 a.m., Christoph Hellwig wrote:
> 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.
> 

Ok. That sounds good to me. I will make the suggested changes and run 
some tests before sending out the V2 patch.

Thank you,
Thomas