From fa33eacd1f259bb8a4a04aba5ba0f9b061e413af Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ga=C3=ABtan=20Harter?= <gaetan.harter@fu-berlin.de>
Date: Mon, 20 Nov 2017 14:32:33 +0100
Subject: [PATCH] crypto/ccm: fix _fits_in_nbytes function
Function is broken with num_bytes >= 4.
Could happen when storing input_len with len_encoding >= 4.
It can take values from 2 to 8, so make it work for cases it would overflow.
---
sys/crypto/modes/ccm.c | 7 +++++--
.../tests-crypto/tests-crypto-modes-ccm.c | 20 +++++++++++++++++++
2 files changed, 25 insertions(+), 2 deletions(-)
diff --git a/sys/crypto/modes/ccm.c b/sys/crypto/modes/ccm.c
index 0442e8abe1..0df28fa4bd 100644
--- a/sys/crypto/modes/ccm.c
+++ b/sys/crypto/modes/ccm.c
@@ -132,8 +132,11 @@ int ccm_compute_adata_mac(cipher_t* cipher, uint8_t* auth_data,
/* Check if 'value' can be stored in 'num_bytes' */
static inline int _fits_in_nbytes(size_t value, uint8_t num_bytes)
{
- uint32_t length_max = 1 << (8 * num_bytes);
- return value < length_max;
+ /* Not allowed to shift more or equal than left operand width
+ * So we shift by maximum num bits of size_t -1 and compare to 1
+ */
+ unsigned shift = (8 * min(sizeof(size_t), num_bytes)) - 1;
+ return (value >> shift) <= 1;
}
diff --git a/tests/unittests/tests-crypto/tests-crypto-modes-ccm.c b/tests/unittests/tests-crypto/tests-crypto-modes-ccm.c
index 81f1d7d654..1fe20e7972 100644
--- a/tests/unittests/tests-crypto/tests-crypto-modes-ccm.c
+++ b/tests/unittests/tests-crypto/tests-crypto-modes-ccm.c
@@ -226,6 +226,26 @@ static void test_crypto_modes_ccm_check_len(void)
TEST_ASSERT_EQUAL_INT(CCM_ERR_INVALID_LENGTH_ENCODING, ret);
ret = _test_ccm_len(cipher_decrypt_ccm, 2, NULL, 1 << 16, 65535);
TEST_ASSERT_EQUAL_INT(CCM_ERR_INVALID_LENGTH_ENCODING, ret);
+
+ /* Valid length that were wrongly checked */
+ /* Check should work with len_encoding >= 4, test with 8 */
+ uint8_t input[8];
+ ret = _test_ccm_len(cipher_encrypt_ccm, 8, input, 8, 0);
+ TEST_ASSERT_MESSAGE(ret > 0, "Encryption : failed with valid input_len");
+
+ /* einput is encrypted value for
+ * - 8 * 0 input
+ * - All 0 nonce and key
+ * - adata_len == 0
+ * - mac_len == 8 and len_encoding = 8
+ */
+ uint8_t einput[16] = {
+ 0xa2, 0x46, 0x75, 0xfc, 0x5f, 0x1b, 0x01, 0x37,
+ 0x8a, 0x85, 0xd7, 0xf8, 0x42, 0x82, 0x6a, 0x63,
+ };
+
+ ret = _test_ccm_len(cipher_decrypt_ccm, 8, einput, 16, 0);
+ TEST_ASSERT_MESSAGE(ret > 0, "Decryption : failed with valid input_len");
}
--
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