From 321adb297c1c19be2d2120658cd43929e5f3faa4 Mon Sep 17 00:00:00 2001
From: Gilles Peskine <Gilles.Peskine@arm.com>
Date: Thu, 10 Oct 2019 19:18:21 +0200
Subject: [PATCH] ASN1 tests: Match "Empty INTEGER" with the actual library
 behavior

mbedtls_asn1_get_int() and mbedtls_asn1_get_mpi() behave differently
on an empty INTEGER (0200). Don't change the library behavior for now
because this might break interoperability in some applications. Write
a test function that matches the library behavior.
---
 tests/suites/test_suite_asn1parse.data     |  3 +-
 tests/suites/test_suite_asn1parse.function | 35 ++++++++++++++++++++++
 2 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/tests/suites/test_suite_asn1parse.data b/tests/suites/test_suite_asn1parse.data
index c5d9136b7..e9172413d 100644
--- a/tests/suites/test_suite_asn1parse.data
+++ b/tests/suites/test_suite_asn1parse.data
@@ -164,8 +164,7 @@ Not BOOLEAN
 get_boolean:"020101":0:MBEDTLS_ERR_ASN1_UNEXPECTED_TAG
 
 Empty INTEGER
-depends_on:SUPPORT_NEGATIVE_INTEGERS
-get_integer:"0200":"":MBEDTLS_ERR_ASN1_INVALID_LENGTH
+empty_integer:"0200"
 
 INTEGER 0
 get_integer:"020100":"0":0
diff --git a/tests/suites/test_suite_asn1parse.function b/tests/suites/test_suite_asn1parse.function
index 049763142..f794db7fc 100644
--- a/tests/suites/test_suite_asn1parse.function
+++ b/tests/suites/test_suite_asn1parse.function
@@ -250,6 +250,41 @@ void get_boolean( const data_t *input,
 }
 /* END_CASE */
 
+/* BEGIN_CASE */
+void empty_integer( const data_t *input )
+{
+    unsigned char *p;
+#if defined(MBEDTLS_BIGNUM_C)
+    mbedtls_mpi actual_mpi;
+#endif
+    int val;
+
+#if defined(MBEDTLS_BIGNUM_C)
+    mbedtls_mpi_init( & actual_mpi );
+#endif
+
+    /* An INTEGER with no content is not valid. */
+    p = input->x;
+    TEST_EQUAL( mbedtls_asn1_get_int( &p, input->x + input->len, &val ),
+                MBEDTLS_ERR_ASN1_INVALID_LENGTH );
+
+#if defined(MBEDTLS_BIGNUM_C)
+    /* INTEGERs are sometimes abused as bitstrings, so the library accepts
+     * an INTEGER with empty content and gives it the value 0. */
+    p = input->x;
+    TEST_EQUAL( mbedtls_asn1_get_mpi( &p, input->x + input->len, &actual_mpi ),
+                0 );
+    TEST_EQUAL( mbedtls_mpi_cmp_int( &actual_mpi, 0 ), 0 );
+#endif
+
+exit:
+#if defined(MBEDTLS_BIGNUM_C)
+    mbedtls_mpi_free( &actual_mpi );
+#endif
+    /*empty cleanup in some configurations*/ ;
+}
+/* END_CASE */
+
 /* BEGIN_CASE */
 void get_integer( const data_t *input,
                   const char *expected_hex, int expected_result )