commit 5299a42f257ad0a43f2bedd9925f8423f3f02245
author Arto Kinnunen <arto.kinnunen@arm.com> Mon Nov 25 16:19:25 2019 +0200
committer Arto Kinnunen <arto.kinnunen@arm.com> Mon Nov 25 16:29:10 2019 +0200
tree 66ea3d0891a2ade8b986ebe4644bb3a9263d8059
parent 5b3669377404b2e35696e2d192a06cecd083d663

Update HMAC and MD FI countermeasures

-Return error value by default.
-Success is returned only after checking internal states.
-Append flow_control to cover also last function call.

library/md.c

diff --git a/library/md.c b/library/md.c
index 7644ac6..777b43c 100644
--- a/library/md.c
+++ b/library/md.c
@@ -525,7 +525,7 @@
     int ret;
     unsigned char sum[MBEDTLS_MD_MAX_SIZE];
     unsigned char *ipad, *opad;
-    size_t i;
+    size_t i = 0;
 
     mbedtls_md_handle_t md_info;
 
@@ -588,16 +588,14 @@
 cleanup:
     mbedtls_platform_zeroize( sum, sizeof( sum ) );
 
-    if ( ret == 0 )
-    {
-        ret = MBEDTLS_ERR_PLATFORM_FAULT_DETECTED;
-        /* Check possible fault injection */
-        if ( ( i - 2 ) == keylen ) {
-            ret = 0;
-        }
-    }
+    if ( ret != 0 )
+        return ret;
 
-    return( ret );
+    /* Check possible fault injection */
+    if ( ( i - 2 ) == keylen )
+        return ret; // success, return 0 from ret
+
+    return( MBEDTLS_ERR_PLATFORM_FAULT_DETECTED );
 }
 
 int mbedtls_md_hmac_update( mbedtls_md_context_t *ctx,