dma-buf/dma-resv: Stop leaking on krealloc() failure

Currently dma_resv_get_fences() will leak the previously
allocated array if the fence iteration got restarted and
the krealloc_array() fails.

Free the old array by hand, and make sure we still clear
the returned *fences so the caller won't end up accessing
freed memory. Some (but not all) of the callers of
dma_resv_get_fences() seem to still trawl through the
array even when dma_resv_get_fences() failed. And let's
zero out *num_fences as well for good measure.

Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Christian König <christian.koenig@amd.com>
Cc: linux-media@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Cc: linaro-mm-sig@lists.linaro.org
Fixes: d3c80698 ("dma-buf: use new iterator in dma_resv_get_fences v3")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Cc: stable@vger.kernel.org
Link: https://patchwork.freedesktop.org/patch/msgid/20230713194745.1751-1-ville.syrjala@linux.intel.comSigned-off-by: Christian König <christian.koenig@amd.com>

drivers/dma-buf/dma-resv.c

@@ -571,6 +571,7 @@ int dma_resv_get_fences(struct dma_resv *obj, enum dma_resv_usage usage,
 	dma_resv_for_each_fence_unlocked(&cursor, fence) {
 
 		if (dma_resv_iter_is_restarted(&cursor)) {
+			struct dma_fence **new_fences;
 			unsigned int count;
 
 			while (*num_fences)
@@ -579,13 +580,17 @@ int dma_resv_get_fences(struct dma_resv *obj, enum dma_resv_usage usage,
 			count = cursor.num_fences + 1;
 
 			/* Eventually re-allocate the array */
-			*fences = krealloc_array(*fences, count,
-						 sizeof(void *),
-						 GFP_KERNEL);
-			if (count && !*fences) {
+			new_fences = krealloc_array(*fences, count,
+						    sizeof(void *),
+						    GFP_KERNEL);
+			if (count && !new_fences) {
+				kfree(*fences);
+				*fences = NULL;
+				*num_fences = 0;
 				dma_resv_iter_end(&cursor);
 				return -ENOMEM;
 			}
+			*fences = new_fences;
 		}
 
 		(*fences)[(*num_fences)++] = dma_fence_get(fence);