2022-10-30 13:06:49

by Dawei Li

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

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 <[email protected]>
---
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

2022-10-30 23:44:28

by Andrew Davis

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

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 <[email protected]>
> ---
> 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;
> }
>