signing: copy content of root HDNode in signing_init

Instead of just storing a pointer, store the content, in case they
later get overwritten.

firmware/signing.c

@@ -28,11 +28,12 @@
 #include "secp256k1.h"
 #include "gettext.h"
 #include "messages.pb.h"
+#include "memzero.h"
 
 static uint32_t inputs_count;
 static uint32_t outputs_count;
 static const CoinInfo *coin;
-static const HDNode *root;
+static CONFIDENTIAL HDNode root;
 static CONFIDENTIAL HDNode node;
 static bool signing = false;
 enum {
@@ -457,7 +458,7 @@ bool compile_input_script_sig(TxInputType *tinput)
 			return false;
 		}
 	}
-	memcpy(&node, root, sizeof(HDNode));
+	memcpy(&node, &root, sizeof(HDNode));
 	if (hdnode_private_ckd_cached(&node, tinput->address_n, tinput->address_n_count, NULL) == 0) {
 		// Failed to derive private key
 		return false;
@@ -478,7 +479,7 @@ void signing_init(const SignTx *msg, const CoinInfo *_coin, const HDNode *_root)
 	inputs_count = msg->inputs_count;
 	outputs_count = msg->outputs_count;
 	coin = _coin;
-	root = _root;
+	memcpy(&root, _root, sizeof(HDNode));
 	version = msg->version;
 	lock_time = msg->lock_time;
 	expiry = msg->expiry;
@@ -659,7 +660,7 @@ static bool signing_check_output(TxOutputType *txoutput) {
 		return false;
 	}
 	spending += txoutput->amount;
-	int co = compile_output(coin, root, txoutput, &bin_output, !is_change);
+	int co = compile_output(coin, &root, txoutput, &bin_output, !is_change);
 	if (!is_change) {
 		layoutProgress(_("Signing transaction"), progress);
 	}
@@ -1207,7 +1208,7 @@ void signing_txack(TransactionType *tx)
 			return;
 		case STAGE_REQUEST_4_OUTPUT:
 			progress = 500 + ((signatures * progress_step + (inputs_count + idx2) * progress_meta_step) >> PROGRESS_PRECISION);
-			if (compile_output(coin, root, tx->outputs, &bin_output, false) <= 0) {
+			if (compile_output(coin, &root, tx->outputs, &bin_output, false) <= 0) {
 				fsm_sendFailure(FailureType_Failure_ProcessError, _("Failed to compile output"));
 				signing_abort();
 				return;
@@ -1330,7 +1331,7 @@ void signing_txack(TransactionType *tx)
 			return;
 
 		case STAGE_REQUEST_5_OUTPUT:
-			if (compile_output(coin, root, tx->outputs, &bin_output,false) <= 0) {
+			if (compile_output(coin, &root, tx->outputs, &bin_output,false) <= 0) {
 				fsm_sendFailure(FailureType_Failure_ProcessError, _("Failed to compile output"));
 				signing_abort();
 				return;
@@ -1428,4 +1429,6 @@ void signing_abort(void)
 		layoutHome();
 		signing = false;
 	}
+	memzero(&root, sizeof(root));
+	memzero(&node, sizeof(node));
 }