Use fewer magic numbers in TLS-Exporter functions
Signed-off-by: Max Fillinger <maximilian.fillinger@foxcrypto.com>
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index a62d4e1..d8fbd77 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -8942,36 +8942,43 @@
const int use_context)
{
int ret = 0;
- size_t prf_input_len = use_context ? 64 + 2 + context_len : 64;
unsigned char *prf_input = NULL;
- if (use_context && context_len >= (1 << 16)) {
- ret = MBEDTLS_ERR_SSL_BAD_INPUT_DATA;
- goto exit;
- }
-
- prf_input = mbedtls_calloc(prf_input_len, sizeof(unsigned char));
- if (prf_input == NULL) {
- ret = MBEDTLS_ERR_SSL_ALLOC_FAILED;
- goto exit;
- }
-
/* The input to the PRF is client_random, then server_random.
* If a context is provided, this is then followed by the context length
* as a 16-bit big-endian integer, and then the context itself. */
- memcpy(prf_input, ssl->transform->randbytes + 32, 32);
- memcpy(prf_input + 32, ssl->transform->randbytes, 32);
+ const size_t randbytes_len = MBEDTLS_CLIENT_HELLO_RANDOM_LEN + MBEDTLS_SERVER_HELLO_RANDOM_LEN;
+ size_t prf_input_len = randbytes_len;
if (use_context) {
- prf_input[64] = (unsigned char) ((context_len >> 8) & 0xff);
- prf_input[65] = (unsigned char) (context_len & 0xff);
- memcpy(prf_input + 66, context, context_len);
+ if (context_len > UINT16_MAX) {
+ return MBEDTLS_ERR_SSL_BAD_INPUT_DATA;
+ }
+
+ /* This does not overflow a 32-bit size_t because the current value of
+ * prf_input_len is 64 (length of client_random + server_random) and
+ * context_len fits into two bytes (checked above). */
+ prf_input_len += sizeof(uint16_t) + context_len;
}
- ret = tls_prf_generic(hash_alg, ssl->session->master, 48,
+
+ prf_input = mbedtls_calloc(prf_input_len, sizeof(unsigned char));
+ if (prf_input == NULL) {
+ return MBEDTLS_ERR_SSL_ALLOC_FAILED;
+ }
+
+ memcpy(prf_input,
+ ssl->transform->randbytes + MBEDTLS_SERVER_HELLO_RANDOM_LEN,
+ MBEDTLS_CLIENT_HELLO_RANDOM_LEN);
+ memcpy(prf_input + MBEDTLS_CLIENT_HELLO_RANDOM_LEN,
+ ssl->transform->randbytes,
+ MBEDTLS_SERVER_HELLO_RANDOM_LEN);
+ if (use_context) {
+ MBEDTLS_PUT_UINT16_BE(context_len, prf_input, randbytes_len);
+ memcpy(prf_input + randbytes_len + sizeof(uint16_t), context, context_len);
+ }
+ ret = tls_prf_generic(hash_alg, ssl->session->master, sizeof(ssl->session->master),
label, label_len,
prf_input, prf_input_len,
out, key_len);
-
-exit:
mbedtls_free(prf_input);
return ret;
}
@@ -8991,7 +8998,11 @@
const size_t hash_len = PSA_HASH_LENGTH(hash_alg);
const unsigned char *secret = ssl->session->app_secrets.exporter_master_secret;
- if (key_len > 0xffff || label_len > 250) {
+ /* Check that the label and key_len fit into the HkdfLabel struct as defined
+ * in RFC 8446, Section 7.1. key_len must fit into an uint16 and the label
+ * must be at most 250 bytes long. (The struct allows up to 256 bytes for
+ * the label, but it is prefixed with "tls13 ".) */
+ if (key_len > UINT16_MAX || label_len > 250) {
return MBEDTLS_ERR_SSL_BAD_INPUT_DATA;
}