ANDROID: binder: retry security_secid_to_secctx()

security_secid_to_secctx() can fail because of a GFP_ATOMIC allocation
This needs to be retried from userspace. However, binder driver doesn't
propagate specific enough error codes just yet (WIP b/28321379). We'll
retry on the binder driver as a temporary work around until userspace
can do this instead.

Bug: 174806915
Signed-off-by: Carlos Llamas <cmllamas@google.com>
Change-Id: Ifebddeb7adf9707613512952b97ab702f0d2d592

drivers/android/binder.c

@@ -3234,9 +3234,28 @@ static void binder_transaction(struct binder_proc *proc,
 	if (target_node && target_node->txn_security_ctx) {
 		u32 secid;
 		size_t added_size;
+		int max_retries = 100;
 
 		security_task_getsecid(proc->tsk, &secid);
+ retry_alloc:
 		ret = security_secid_to_secctx(secid, &secctx, &secctx_sz);
+		if (ret == -ENOMEM && max_retries-- > 0) {
+			struct page *dummy_page;
+
+			/*
+			 * security_secid_to_secctx() can fail because of a
+			 * GFP_ATOMIC allocation in which case -ENOMEM is
+			 * returned. This needs to be retried, but there is
+			 * currently no way to tell userspace to retry so we
+			 * do it here. We make sure there is still available
+			 * memory first and then retry.
+			 */
+			dummy_page = alloc_page(GFP_KERNEL);
+			if (dummy_page) {
+				__free_page(dummy_page);
+				goto retry_alloc;
+			}
+		}
 		if (ret) {
 			return_error = BR_FAILED_REPLY;
 			return_error_param = ret;