[Linaro-mm-sig] Re: [PATCH v2] dma-buf: fix racing conflict of dma_heap_add()

On Mon, Oct 31, 2022 at 7:53 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@TYCP286MB...

v1->v2: Narrow down locking scope, check the existence of heap before insertion, as suggested by Andrew Davis.

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 | 37 ++++++++++++++++++++++++++++--------- 1 file changed, 28 insertions(+), 9 deletions(-)

diff --git a/drivers/dma-buf/dma-heap.c b/drivers/dma-buf/dma-heap.c index 8f5848aa144f..1c787a147e3a 100644 --- a/drivers/dma-buf/dma-heap.c +++ b/drivers/dma-buf/dma-heap.c @@ -216,9 +216,21 @@ const char *dma_heap_get_name(struct dma_heap *heap) return heap->name; }

+static inline bool dma_heap_exist(const char *name) +{

•   struct dma_heap *h;
  

•   list_for_each_entry(h, &heap_list, list) {
  

•           if (!strcmp(h->name, name))
  

•                   return true;
  

•   }
  

•   return false;
  

+}

struct dma_heap *dma_heap_add(const struct dma_heap_export_info *exp_info) {

•   struct dma_heap *heap, *h, *err_ret;
  

•   struct dma_heap *heap, *err_ret;
    struct device *dev_ret;
    unsigned int minor;
    int ret;
  

@@ -235,13 +247,11 @@ struct dma_heap *dma_heap_add(const struct dma_heap_export_info *exp_info)

    /* 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);
  

•           }
  

•   if (dma_heap_exist(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);
  

Hi Dawei, What Andrew was suggesting was that you entirely move the check from here to the critical section down below, not duplicate the check. I don't think we want to check this twice. We should be able to do this by taking the heap_list_lock only once.

    }
    mutex_unlock(&heap_list_lock);

@@ -283,13 +293,22 @@ 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);
  

•   if (unlikely(dma_heap_exist(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;
  

•   }
    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