linux-kernel - Re: [PATCH v3] dma-buf: fix racing conflict of dma_heap

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Date:   Wed, 2 Nov 2022 12:13:39 -0500
From:   Andrew Davis <afd@...com>
To:     Dawei Li <set_pte_at@...look.com>, <sumit.semwal@...aro.org>,
        <christian.koenig@....com>
CC:     <benjamin.gaignard@...labora.com>, <labbott@...hat.com>,
        <Brian.Starkey@....com>, <jstultz@...gle.com>,
        <sspatil@...roid.com>, <linux-media@...r.kernel.org>,
        <dri-devel@...ts.freedesktop.org>,
        <linaro-mm-sig@...ts.linaro.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] dma-buf: fix racing conflict of dma_heap_add()

On 11/2/22 10:58 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.
> 
> v1: https://lore.kernel.org/all/TYCP286MB2323950197F60FC3473123B7CA349@TYCP286MB2323.JPNP286.PROD.OUTLOOK.COM/
> 
> v1->v2: Narrow down locking scope, check the existence of heap before
> insertion, as suggested by Andrew Davis.
> 
> v2->v3: Remove double checking.

The above version info should be in a cover letter or below
the --- line so it doesn't end up in the commit message in tree.

> 
> Fixes: c02a81fba74f ("dma-buf: Add dma-buf heaps framework")
> 
> base-commit: 447fb14bf07905b880c9ed1ea92c53d6dd0649d7
> 

Same as above, plus this is an odd base, maybe just use "v6.1-rc2".

> Signed-off-by: Dawei Li <set_pte_at@...look.com>
> ---
>   drivers/dma-buf/dma-heap.c | 29 +++++++++++++++--------------
>   1 file changed, 15 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/dma-buf/dma-heap.c b/drivers/dma-buf/dma-heap.c
> index 8f5848aa144f..7a25e98259ea 100644
> --- a/drivers/dma-buf/dma-heap.c
> +++ b/drivers/dma-buf/dma-heap.c
> @@ -233,18 +233,6 @@ struct dma_heap *dma_heap_add(const struct dma_heap_export_info *exp_info)
>   		return ERR_PTR(-EINVAL);
>   	}
>   
> -	/* check the name is unique */
> -	mutex_lock(&heap_list_lock);
> -	list_for_each_entry(h, &heap_list, list) {
> -		if (!strcmp(h->name, exp_info->name)) {
> -			mutex_unlock(&heap_list_lock);
> -			pr_err("dma_heap: Already registered heap named %s\n",
> -			       exp_info->name);
> -			return ERR_PTR(-EINVAL);
> -		}
> -	}
> -	mutex_unlock(&heap_list_lock);
> -
>   	heap = kzalloc(sizeof(*heap), GFP_KERNEL);
>   	if (!heap)
>   		return ERR_PTR(-ENOMEM);
> @@ -283,13 +271,26 @@ struct dma_heap *dma_heap_add(const struct dma_heap_export_info *exp_info)
>   		err_ret = ERR_CAST(dev_ret);
>   		goto err2;
>   	}
> -	/* Add heap to the list */
> +
>   	mutex_lock(&heap_list_lock);
> +	/* check the name is unique */
> +	list_for_each_entry(h, &heap_list, list) {
> +		if (!strcmp(h->name, exp_info->name)) {
> +			mutex_unlock(&heap_list_lock);
> +			pr_err("dma_heap: Already registered heap named %s\n",
> +			       exp_info->name);
> +			err_ret = ERR_PTR(-EINVAL);
> +			goto err3;
> +		}
> +	}
> +
> +	/* Add heap to the list */
>   	list_add(&heap->list, &heap_list);
>   	mutex_unlock(&heap_list_lock);
>   
>   	return heap;
> -

Would like to keep this new line after the return statement.

Andrew

> +err3:
> +	device_destroy(dma_heap_class, heap->heap_devt);
>   err2:
>   	cdev_del(&heap->heap_cdev);
>   err1: