[PATCH v2] dma-buf: fix racing conflict of dma_heap_add()

[Dawei Li <set_pte_at@xxxxxxxxxxx>]

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@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/

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@xxxxxxxxxxx>
---
 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);
 	}
 	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