From 33ca6af8a3bd770cb454793b9f6fc52e5d43bb21 Mon Sep 17 00:00:00 2001
From: Andrzej Kurek <Andrzej.Kurek@arm.com>
Date: Wed, 1 Dec 2021 21:58:05 +0100
Subject: [PATCH] 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>
---
 library/cipher.c                             |  6 +++
 tests/suites/test_suite_cipher.chacha20.data | 20 ++++++++++
 tests/suites/test_suite_cipher.function      | 41 ++++++++++++++++++++
 3 files changed, 67 insertions(+)

diff --git a/library/cipher.c b/library/cipher.c
index 03e84c6c8..39c105cfb 100644
--- a/library/cipher.c
+++ b/library/cipher.c
@@ -386,6 +386,12 @@ int mbedtls_cipher_set_iv( mbedtls_cipher_context_t *ctx,
 #if defined(MBEDTLS_CHACHA20_C)
     if ( ctx->cipher_info->type == MBEDTLS_CIPHER_CHACHA20 )
     {
+        /* Even though the actual_iv_size is overwritten with a correct value
+         * of 12 from the cipher info, return an error to indicate that
+         * the input iv_len is wrong. */
+        if( iv_len != 12 )
+            return( MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
+
         if ( 0 != mbedtls_chacha20_starts( (mbedtls_chacha20_context*)ctx->cipher_ctx,
                                            iv,
                                            0U ) ) /* Initial counter value */
diff --git a/tests/suites/test_suite_cipher.chacha20.data b/tests/suites/test_suite_cipher.chacha20.data
index 11de1038a..117fce339 100644
--- a/tests/suites/test_suite_cipher.chacha20.data
+++ b/tests/suites/test_suite_cipher.chacha20.data
@@ -109,3 +109,23 @@ enc_dec_buf_multipart:MBEDTLS_CIPHER_CHACHA20:256:6:16:-1:6:16:6:16
 ChaCha20 Encrypt and decrypt 32 bytes in multiple parts
 depends_on:MBEDTLS_CHACHA20_C
 enc_dec_buf_multipart:MBEDTLS_CIPHER_CHACHA20:256:16:16:-1:16:16:16:16
+
+ChaCha20 IV Length 0
+depends_on:MBEDTLS_CHACHA20_C
+check_iv:MBEDTLS_CIPHER_CHACHA20:"CHACHA20":0:MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA
+
+ChaCha20 IV Length 11
+depends_on:MBEDTLS_CHACHA20_C
+check_iv:MBEDTLS_CIPHER_CHACHA20:"CHACHA20":11:MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA
+
+ChaCha20 IV Length 12
+depends_on:MBEDTLS_CHACHA20_C
+check_iv:MBEDTLS_CIPHER_CHACHA20:"CHACHA20":12:0
+
+ChaCha20 IV Length 13
+depends_on:MBEDTLS_CHACHA20_C
+check_iv:MBEDTLS_CIPHER_CHACHA20:"CHACHA20":13:MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA
+
+ChaCha20 IV Length 16
+depends_on:MBEDTLS_CHACHA20_C
+check_iv:MBEDTLS_CIPHER_CHACHA20:"CHACHA20":16:MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA
diff --git a/tests/suites/test_suite_cipher.function b/tests/suites/test_suite_cipher.function
index fd2985b5e..c837a69bd 100644
--- a/tests/suites/test_suite_cipher.function
+++ b/tests/suites/test_suite_cipher.function
@@ -442,6 +442,8 @@ void enc_dec_buf( int cipher_id, char * cipher_string, int key_len,
     if( NULL != strstr( cipher_info->name, "CCM*-NO-TAG") )
         iv_len = 13; /* For CCM, IV length is expected to be between 7 and 13 bytes.
                       * For CCM*-NO-TAG, IV length must be exactly 13 bytes long. */
+    else if( cipher_info->type == MBEDTLS_CIPHER_CHACHA20 )
+        iv_len = 12;
     else
         iv_len = sizeof(iv);
 
@@ -689,6 +691,8 @@ void enc_dec_buf_multipart( int cipher_id, int key_len, int first_length_val,
     if( NULL != strstr( cipher_info->name, "CCM*-NO-TAG") )
         iv_len = 13; /* For CCM, IV length is expected to be between 7 and 13 bytes.
                       * For CCM*-NO-TAG, IV length must be exactly 13 bytes long. */
+    else if( cipher_info->type == MBEDTLS_CIPHER_CHACHA20 )
+        iv_len = 12;
     else
         iv_len = sizeof(iv);
 
@@ -1130,3 +1134,40 @@ void check_padding( int pad_mode, data_t * input, int ret, int dlen_check
         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 );
+    TEST_ASSERT( strcmp( mbedtls_cipher_info_get_name( cipher_info ),
+                         cipher_string ) == 0 );
+
+    /* 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 */