linux-kernel - Re: [PATCH 1/3] udmabuf: Keep track current device mappings

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Date: Thu, 25 Jan 2024 09:22:58 -0600
From: Andrew Davis <afd@...com>
To: "Kasireddy, Vivek" <vivek.kasireddy@...el.com>,
        Gerd Hoffmann
	<kraxel@...hat.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Christian König <christian.koenig@....com>,
        Paul Cercueil
	<paul@...pouillou.net>
CC: "linaro-mm-sig@...ts.linaro.org" <linaro-mm-sig@...ts.linaro.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>
Subject: Re: [PATCH 1/3] udmabuf: Keep track current device mappings

On 1/24/24 4:36 PM, Kasireddy, Vivek wrote:
> Hi Andrew,
> 
>> When a device attaches to and maps our buffer we need to keep track
>> of this mapping/device. This is needed for synchronization with these
>> devices when beginning and ending CPU access for instance. Add a list
>> that tracks device mappings as part of {map,unmap}_udmabuf().
>>
>> Signed-off-by: Andrew Davis <afd@...com>
>> ---
>>   drivers/dma-buf/udmabuf.c | 43
>> +++++++++++++++++++++++++++++++++++++--
>>   1 file changed, 41 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c
>> index c406459996489..3a23f0a7d112a 100644
>> --- a/drivers/dma-buf/udmabuf.c
>> +++ b/drivers/dma-buf/udmabuf.c
>> @@ -28,6 +28,14 @@ struct udmabuf {
>>   	struct page **pages;
>>   	struct sg_table *sg;
>>   	struct miscdevice *device;
>> +	struct list_head attachments;
>> +	struct mutex lock;
>> +};
>> +
>> +struct udmabuf_attachment {
>> +	struct device *dev;
>> +	struct sg_table *table;
>> +	struct list_head list;
>>   };
>>
>>   static vm_fault_t udmabuf_vm_fault(struct vm_fault *vmf)
>> @@ -120,14 +128,42 @@ static void put_sg_table(struct device *dev, struct
>> sg_table *sg,
>>   static struct sg_table *map_udmabuf(struct dma_buf_attachment *at,
>>   				    enum dma_data_direction direction)
>>   {
>> -	return get_sg_table(at->dev, at->dmabuf, direction);
>> +	struct udmabuf *ubuf = at->dmabuf->priv;
>> +	struct udmabuf_attachment *a;
>> +
>> +	a = kzalloc(sizeof(*a), GFP_KERNEL);
>> +	if (!a)
>> +		return ERR_PTR(-ENOMEM);
>> +
>> +	a->table = get_sg_table(at->dev, at->dmabuf, direction);
>> +	if (IS_ERR(a->table)) {
>> +		kfree(a);
>> +		return a->table;
> Isn't that a use-after-free bug?

Indeed it is, will fix.

Seems coccicheck also caught this but I missed it when
reviewing its output, my bad :(

Andrew

> Rest of the patch lgtm.
> 
> Thanks,
> Vivek
> 
>> +	}
>> +
>> +	a->dev = at->dev;
>> +
>> +	mutex_lock(&ubuf->lock);
>> +	list_add(&a->list, &ubuf->attachments);
>> +	mutex_unlock(&ubuf->lock);
>> +
>> +	return a->table;
>>   }
>>
>>   static void unmap_udmabuf(struct dma_buf_attachment *at,
>>   			  struct sg_table *sg,
>>   			  enum dma_data_direction direction)
>>   {
>> -	return put_sg_table(at->dev, sg, direction);
>> +	struct udmabuf_attachment *a = at->priv;
>> +	struct udmabuf *ubuf = at->dmabuf->priv;
>> +
>> +	mutex_lock(&ubuf->lock);
>> +	list_del(&a->list);
>> +	mutex_unlock(&ubuf->lock);
>> +
>> +	put_sg_table(at->dev, sg, direction);
>> +
>> +	kfree(a);
>>   }
>>
>>   static void release_udmabuf(struct dma_buf *buf)
>> @@ -263,6 +299,9 @@ static long udmabuf_create(struct miscdevice
>> *device,
>>   		memfd = NULL;
>>   	}
>>
>> +	INIT_LIST_HEAD(&ubuf->attachments);
>> +	mutex_init(&ubuf->lock);
>> +
>>   	exp_info.ops  = &udmabuf_ops;
>>   	exp_info.size = ubuf->pagecount << PAGE_SHIFT;
>>   	exp_info.priv = ubuf;
>> --
>> 2.39.2
>