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From:   "T.J. Mercier" <tjmercier@google.com>
Date:   Wed, 2 Nov 2022 09:54:03 -0700
Message-ID: <CABdmKX3bE5eKOeonTnkLZUgg=1yx3h5QPkGgue-bATHVDChHLQ@mail.gmail.com>
Subject: Re: [PATCH v3] dma-buf: fix racing conflict of dma_heap_add()
To:     Dawei Li <set_pte_at@outlook.com>
Cc:     sumit.semwal@linaro.org, christian.koenig@amd.com,
        benjamin.gaignard@collabora.com, labbott@redhat.com,
        Brian.Starkey@arm.com, jstultz@google.com, afd@ti.com,
        sspatil@android.com, linux-media@vger.kernel.org,
        dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org,
        linux-kernel@vger.kernel.org
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On Wed, Nov 2, 2022 at 8:59 AM Dawei Li <set_pte_at@outlook.com> 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.
>
> 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 | 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;
> -
> +err3:
> +       device_destroy(dma_heap_class, heap->heap_devt);
>  err2:
>         cdev_del(&heap->heap_cdev);
>  err1:
> --
> 2.25.1
>

Reviewed-by: T.J. Mercier <tjmercier@google.com>

Thanks!