From: Thomas Tai <thomas.tai@oracle.com>
To: Christoph Hellwig <hch@lst.de>
Cc: iommu@lists.linux-foundation.org, robin.murphy@arm.com,
linux-kernel@vger.kernel.org, konrad.wilk@oracle.com
Subject: Re: [PATCH] dma-direct: Fix potential NULL pointer dereference
Date: Tue, 15 Sep 2020 10:11:51 -0400 [thread overview]
Message-ID: <f5cba632-421a-f375-3697-51a182a53a32@oracle.com> (raw)
In-Reply-To: <20200915140719.GA14831@lst.de>
On 2020-09-15 10:07 a.m., Christoph Hellwig wrote:
> On Tue, Sep 15, 2020 at 08:03:14AM -0600, Thomas Tai wrote:
>> When booting the kernel v5.9-rc4 on a VM, the kernel would panic when
>> printing a warning message in swiotlb_map(). It is because dev->dma_mask
>> can potentially be a null pointer. Using the dma_get_mask() macro can
>> avoid the NULL pointer dereference.
>
> dma_mask must not be zero. This means drm is calling DMA API functions
> on something weird. This needs to be fixed in the caller.
>
Thanks, Christoph for your comment. The caller already fixed the null
pointer in the latest v5.9-rc5. I am thinking that if we had used the
dma_get_mask(), the kernel couldn't panic and could properly print out
the warning message.
Thomas
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next prev parent reply other threads:[~2020-09-15 14:12 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-15 14:03 [PATCH] dma-direct: Fix potential NULL pointer dereference Thomas Tai
2020-09-15 14:07 ` Christoph Hellwig
2020-09-15 14:08 ` Christoph Hellwig
2020-09-15 14:11 ` Thomas Tai [this message]
2020-09-15 14:26 ` Christoph Hellwig
2020-09-15 14:40 ` Thomas Tai
2020-09-15 15:09 ` Christoph Hellwig
2020-09-15 15:12 ` Thomas Tai
2020-09-15 20:46 ` Thomas Tai
2020-09-16 6:19 ` Christoph Hellwig
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