From f7d6acd4754b732084aea5f0a94ecdc6b4156185 Mon Sep 17 00:00:00 2001
From: Gilles Peskine <Gilles.Peskine@arm.com>
Date: Fri, 1 Mar 2019 18:06:08 +0100
Subject: [PATCH] mbedtls_asn1_get_int: allow leading zeros properly

Allow any number of leading zeros, not just based on sizeof(int).
---
 library/asn1parse.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/library/asn1parse.c b/library/asn1parse.c
index 171c340b8..20e8177b6 100644
--- a/library/asn1parse.c
+++ b/library/asn1parse.c
@@ -149,11 +149,18 @@ int mbedtls_asn1_get_int( unsigned char **p,
     if( ( ret = mbedtls_asn1_get_tag( p, end, &len, MBEDTLS_ASN1_INTEGER ) ) != 0 )
         return( ret );
 
-    if( len == 0 || len > sizeof( int ) || ( **p & 0x80 ) != 0 )
+    if( len == 0 || ( **p & 0x80 ) != 0 )
+        return( MBEDTLS_ERR_ASN1_INVALID_LENGTH );
+
+    while( len > 0 && **p == 0 )
+    {
+        ++( *p );
+        --len;
+    }
+    if( len > sizeof( int ) )
         return( MBEDTLS_ERR_ASN1_INVALID_LENGTH );
 
     *val = 0;
-
     while( len-- > 0 )
     {
         *val = ( *val << 8 ) | **p;