Re: [PATCH] dma-buf: fix racing conflict of dma_heap_add()

[Andrew Davis]

On 10/30/22 6:37 AM, Dawei Li wrote:
> Racing conflict could be:
> task A                 task B
> list_for_each_entry
> strcmp(h->name))
>                         list_for_each_entry
>                         strcmp(h->name)
> kzalloc                kzalloc
> ......                 .....
> device_create          device_create
> list_add
>                         list_add
>
> The root cause is that task B has no idea about the fact someone
> else(A) has inserted heap with same name when it calls list_add,
> so a potential collision occurs.
>
> Fixes: c02a81fba74f ("dma-buf: Add dma-buf heaps framework")
>
> base-commit: 447fb14bf07905b880c9ed1ea92c53d6dd0649d7
>
> Signed-off-by: Dawei Li <set_pte_at@xxxxxxxxxxx>
> ---
>   drivers/dma-buf/dma-heap.c | 7 ++++---
>   1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/dma-buf/dma-heap.c b/drivers/dma-buf/dma-heap.c
> index 8f5848aa144f..ff44c2777b04 100644
> --- a/drivers/dma-buf/dma-heap.c
> +++ b/drivers/dma-buf/dma-heap.c
> @@ -243,11 +243,12 @@ struct dma_heap *dma_heap_add(const struct dma_heap_export_info *exp_info)
>   			return ERR_PTR(-EINVAL);
>   		}
>   	}
> -	mutex_unlock(&heap_list_lock);
>   
>   	heap = kzalloc(sizeof(*heap), GFP_KERNEL);
> -	if (!heap)
> +	if (!heap) {
> +		mutex_unlock(&heap_list_lock);
>   		return ERR_PTR(-ENOMEM);
> +	}
>   
>   	heap->name = exp_info->name;
>   	heap->ops = exp_info->ops;
> @@ -284,7 +285,6 @@ struct dma_heap *dma_heap_add(const struct dma_heap_export_info *exp_info)
>   		goto err2;
>   	}
>   	/* Add heap to the list */
> -	mutex_lock(&heap_list_lock);


Good catch!

In general I'd like to hold locks for as short a time as possible and
only bracket the lock associated structure (heap_list). How about we
move the duplicate name check to down here so they are both inside
this one locked section here.

I know this will mean we take a longer unwind error path
if the names are duplicated, but that should be rare and
this will keep all heap_list accesses together.

Thanks,
Andrew


>   	list_add(&heap->list, &heap_list);
>   	mutex_unlock(&heap_list_lock);
>   
> @@ -296,6 +296,7 @@ struct dma_heap *dma_heap_add(const struct dma_heap_export_info *exp_info)
>   	xa_erase(&dma_heap_minors, minor);
>   err0:
>   	kfree(heap);
> +	mutex_unlock(&heap_list_lock);
>   	return err_ret;
>   }
>