Return an error for IV lengths other than 12 with ChaCha20

The implementation was silently overwriting the IV length to 12
even though the caller passed a different value.
Change the behavior to signal that a different length is not supported.
Signed-off-by: Andrzej Kurek <andrzej.kurek@arm.com>
diff --git a/tests/suites/test_suite_cipher.function b/tests/suites/test_suite_cipher.function
index 76e474f..73e548d 100644
--- a/tests/suites/test_suite_cipher.function
+++ b/tests/suites/test_suite_cipher.function
@@ -702,7 +702,7 @@
 void enc_dec_buf( int cipher_id, char * cipher_string, int key_len,
                   int length_val, int pad_mode )
 {
-    size_t length = length_val, outlen, total_len, i, block_size;
+    size_t length = length_val, outlen, total_len, i, block_size, iv_len;
     unsigned char key[64];
     unsigned char iv[16];
     unsigned char ad[13];
@@ -758,8 +758,13 @@
     memset( decbuf, 0, sizeof( decbuf ) );
     memset( tag, 0, sizeof( tag ) );
 
-    TEST_ASSERT( 0 == mbedtls_cipher_set_iv( &ctx_dec, iv, sizeof( iv ) ) );
-    TEST_ASSERT( 0 == mbedtls_cipher_set_iv( &ctx_enc, iv, sizeof( iv ) ) );
+    if( cipher_info->type == MBEDTLS_CIPHER_CHACHA20 )
+        iv_len = 12;
+    else
+        iv_len = sizeof(iv);
+
+    TEST_ASSERT( 0 == mbedtls_cipher_set_iv( &ctx_dec, iv, iv_len ) );
+    TEST_ASSERT( 0 == mbedtls_cipher_set_iv( &ctx_enc, iv, iv_len ) );
 
     TEST_ASSERT( 0 == mbedtls_cipher_reset( &ctx_dec ) );
     TEST_ASSERT( 0 == mbedtls_cipher_reset( &ctx_enc ) );
@@ -953,7 +958,7 @@
     size_t first_length = first_length_val;
     size_t second_length = second_length_val;
     size_t length = first_length + second_length;
-    size_t block_size;
+    size_t block_size, iv_len;
     unsigned char key[32];
     unsigned char iv[16];
 
@@ -998,8 +1003,13 @@
     (void) pad_mode;
 #endif /* MBEDTLS_CIPHER_MODE_WITH_PADDING */
 
-    TEST_ASSERT( 0 == mbedtls_cipher_set_iv( &ctx_dec, iv, 16 ) );
-    TEST_ASSERT( 0 == mbedtls_cipher_set_iv( &ctx_enc, iv, 16 ) );
+    if( cipher_info->type == MBEDTLS_CIPHER_CHACHA20 )
+        iv_len = 12;
+    else
+        iv_len = sizeof(iv);
+
+    TEST_ASSERT( 0 == mbedtls_cipher_set_iv( &ctx_dec, iv, iv_len ) );
+    TEST_ASSERT( 0 == mbedtls_cipher_set_iv( &ctx_enc, iv, iv_len ) );
 
     TEST_ASSERT( 0 == mbedtls_cipher_reset( &ctx_dec ) );
     TEST_ASSERT( 0 == mbedtls_cipher_reset( &ctx_enc ) );
@@ -1578,3 +1588,38 @@
         TEST_ASSERT( dlen == (size_t) dlen_check );
 }
 /* END_CASE */
+
+/* BEGIN_CASE */
+void check_iv( int cipher_id, char * cipher_string,
+               int iv_len_val, int ret )
+{
+    size_t iv_len = iv_len_val;
+    unsigned char iv[16];
+
+    const mbedtls_cipher_info_t *cipher_info;
+    mbedtls_cipher_context_t ctx_dec;
+    mbedtls_cipher_context_t ctx_enc;
+
+    /*
+     * Prepare contexts
+     */
+    mbedtls_cipher_init( &ctx_dec );
+    mbedtls_cipher_init( &ctx_enc );
+
+    /* Check and get info structures */
+    cipher_info = mbedtls_cipher_info_from_type( cipher_id );
+    TEST_ASSERT( NULL != cipher_info );
+    TEST_ASSERT( mbedtls_cipher_info_from_string( cipher_string ) == cipher_info );
+
+    /* Initialise enc and dec contexts */
+    TEST_ASSERT( 0 == mbedtls_cipher_setup( &ctx_dec, cipher_info ) );
+    TEST_ASSERT( 0 == mbedtls_cipher_setup( &ctx_enc, cipher_info ) );
+
+    TEST_ASSERT( ret == mbedtls_cipher_set_iv( &ctx_dec, iv, iv_len ) );
+    TEST_ASSERT( ret == mbedtls_cipher_set_iv( &ctx_enc, iv, iv_len ) );
+
+exit:
+    mbedtls_cipher_free( &ctx_dec );
+    mbedtls_cipher_free( &ctx_enc );
+}
+/* END_CASE */