From 436d18dcaa1d34d9508be7242d4e0ca7398bbfe0 Mon Sep 17 00:00:00 2001
From: Jarno Lamsa <jarno.lamsa@arm.com>
Date: Thu, 3 Oct 2019 11:46:30 +0300
Subject: [PATCH] Prevent a 0-modulus

If given range for a random is [0, 0), return 0.
Modulus 0 is undefined behaviour.
---
 library/platform_util.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/library/platform_util.c b/library/platform_util.c
index 6ba4112fb..9461a9c73 100644
--- a/library/platform_util.c
+++ b/library/platform_util.c
@@ -150,7 +150,17 @@ uint32_t mbedtls_platform_random_in_range( size_t num )
 
     mbedtls_hardware_poll( NULL, (unsigned char *) &result, sizeof( result ),
                            &olen );
-    return( result % num );
+
+    if( num == 0 )
+    {
+        result = 0;
+    }
+    else
+    {
+        result %= num;
+    }
+
+    return( result );
 #endif
 }