drm/amdgpu: fix possible UAF in amdgpu_cs_pass1()

commit 90e0656 upstream.

Since the gang_size check is outside of chunk parsing
loop, we need to reset i before we free the chunk data.

Suggested by Ye Zhang (@VAR10CK) of Baidu Security.

Reviewed-by: Guchun Chen <guchun.chen@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c

@@ -287,7 +287,7 @@ static int amdgpu_cs_pass1(struct amdgpu_cs_parser *p,
 
 	if (!p->gang_size) {
 		ret = -EINVAL;
-		goto free_partial_kdata;
+		goto free_all_kdata;
 	}
 
 	for (i = 0; i < p->gang_size; ++i) {