From 9b3051fb1060e3d783bf9f900295eace740b1c66 Mon Sep 17 00:00:00 2001
From: Minos Galanakis <minos.galanakis@arm.com>
Date: Mon, 2 Jun 2025 14:36:25 +0100
Subject: [PATCH] Built-in lms driver: always zeroize output-buffer in
 create_merkle_leaf_value

Signed-off-by: Minos Galanakis <minos.galanakis@arm.com>
---
 library/lms.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/library/lms.c b/library/lms.c
index 78886ab78d..11e2508954 100644
--- a/library/lms.c
+++ b/library/lms.c
@@ -101,6 +101,9 @@ static int create_merkle_leaf_value(const mbedtls_lms_parameters_t *params,
     size_t output_hash_len;
     unsigned char r_node_idx_bytes[4];
 
+    /* Always zeroize the output buffer to avoid undefined behavior at an early exit */
+    memset(out, 0, MBEDTLS_LMS_M_NODE_BYTES(params->type));
+
     op = psa_hash_operation_init();
     status = psa_hash_setup(&op, PSA_ALG_SHA_256);
     if (status != PSA_SUCCESS) {