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

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

[Dawei Li]

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@outlook.com>
---
 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);
 	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;
 }
 
-- 
2.25.1

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@outlook.com>
> ---
>   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;
>   }
>