dma-buf/sync_file: Don't leak fences on merge failure

Each add_fence() call does a dma_fence_get() on the relevant fence.  In
the error path, we weren't calling dma_fence_put() so all those fences
got leaked.  Also, in the krealloc_array failure case, we weren't
freeing the fences array.  Instead, ensure that i and fences are always
zero-initialized and dma_fence_put() all the fences and kfree(fences) on
every error path.
Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Christian König <christian.koenig@amd.com>
Fixes: a02b9dc9 ("dma-buf/sync_file: refactor fence storage in struct sync_file")
Cc: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Cc: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210624174732.1754546-1-jason@jlekstrand.netSigned-off-by: Christian König <christian.koenig@amd.com>

drivers/dma-buf/sync_file.c

@@ -211,8 +211,8 @@ static struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
 					 struct sync_file *b)
 {
 	struct sync_file *sync_file;
-	struct dma_fence **fences, **nfences, **a_fences, **b_fences;
-	int i, i_a, i_b, num_fences, a_num_fences, b_num_fences;
+	struct dma_fence **fences = NULL, **nfences, **a_fences, **b_fences;
+	int i = 0, i_a, i_b, num_fences, a_num_fences, b_num_fences;
 
 	sync_file = sync_file_alloc();
 	if (!sync_file)
@@ -236,7 +236,7 @@ static struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
 	 * If a sync_file can only be created with sync_file_merge
 	 * and sync_file_create, this is a reasonable assumption.
 	 */
-	for (i = i_a = i_b = 0; i_a < a_num_fences && i_b < b_num_fences; ) {
+	for (i_a = i_b = 0; i_a < a_num_fences && i_b < b_num_fences; ) {
 		struct dma_fence *pt_a = a_fences[i_a];
 		struct dma_fence *pt_b = b_fences[i_b];
 
@@ -277,15 +277,16 @@ static struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
 		fences = nfences;
 	}
 
-	if (sync_file_set_fence(sync_file, fences, i) < 0) {
-		kfree(fences);
+	if (sync_file_set_fence(sync_file, fences, i) < 0)
 		goto err;
-	}
 
 	strlcpy(sync_file->user_name, name, sizeof(sync_file->user_name));
 	return sync_file;
 
 err:
+	while (i)
+		dma_fence_put(fences[--i]);
+	kfree(fences);
 	fput(sync_file->file);
 	return NULL;