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dtls.c: cleanup length checks in dtls_send_client_key_exchange. #299

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dtls.c: cleanup length checks in dtls_send_client_key_exchange. #299

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46 changes: 22 additions & 24 deletions dtls.c
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Original file line number Diff line number Diff line change
Expand Up @@ -166,7 +166,9 @@ memarray_t dtlscontext_storage;
#define DTLS_SKEXECPSK_LENGTH_MIN 2
#define DTLS_SKEXECPSK_LENGTH_MAX 2 + DTLS_PSK_MAX_CLIENT_IDENTITY_LEN
#define DTLS_CKXPSK_LENGTH_MIN 2
#define DTLS_CKXEC_LENGTH (1 + 1 + max(DTLS_EC_KEY_SIZE + DTLS_EC_KEY_SIZE, DTLS_PSK_MAX_CLIENT_IDENTITY_LEN))
#define DTLS_CKXEC_ECDSA_LENGTH (1 + 1 + DTLS_EC_KEY_SIZE + DTLS_EC_KEY_SIZE)
#define DTLS_CKXEC_PSK_LENGTH (2 + DTLS_PSK_MAX_CLIENT_IDENTITY_LEN)
#define DTLS_CKXEC_LENGTH (max(DTLS_CKXEC_ECDSA_LENGTH, DTLS_CKXEC_PSK_LENGTH))
#define DTLS_CV_LENGTH (1 + 1 + 2 + 1 + 1 + 1 + 1 + DTLS_EC_KEY_SIZE + 1 + 1 + DTLS_EC_KEY_SIZE)
#define DTLS_FIN_LENGTH 12

Expand Down Expand Up @@ -1513,7 +1515,7 @@ check_client_keyexchange(dtls_context_t *ctx,
#ifdef DTLS_ECC
if (key_exchange_algorithm == DTLS_KEY_EXCHANGE_ECDHE_ECDSA) {

if (length < DTLS_HS_LENGTH + DTLS_CKXEC_LENGTH) {
if (length < DTLS_HS_LENGTH + DTLS_CKXEC_ECDSA_LENGTH) {
dtls_debug("The client key exchange is too short\n");
return dtls_alert_fatal_create(DTLS_ALERT_HANDSHAKE_FAILURE);
}
Expand Down Expand Up @@ -2969,44 +2971,40 @@ static int
dtls_send_client_key_exchange(dtls_context_t *ctx, dtls_peer_t *peer)
{
uint8 buf[DTLS_CKXEC_LENGTH];
uint8 *p;
uint8 *p = buf;
dtls_handshake_parameters_t *handshake = peer->handshake_params;
const cipher_suite_key_exchange_algorithm_t key_exchange_algorithm =
get_key_exchange_algorithm(handshake->cipher_index);
int ret;

p = buf;

memset(buf, 0, sizeof(buf));
switch (key_exchange_algorithm) {
case DTLS_KEY_EXCHANGE_PSK:
#ifdef DTLS_PSK
{
int len;

int len = 0;
int max_len = min(sizeof(buf) - sizeof(uint16),
sizeof(handshake->keyx.psk.identity));
p += sizeof(uint16);
len = CALL(ctx, get_psk_info, &peer->session, DTLS_PSK_IDENTITY,
handshake->keyx.psk.identity, handshake->keyx.psk.id_length,
buf + sizeof(uint16),
min(sizeof(buf) - sizeof(uint16),
sizeof(handshake->keyx.psk.identity)));
handshake->keyx.psk.identity, handshake->keyx.psk.id_length,
p, max_len);
if (len < 0) {
dtls_crit("no psk identity set in kx\n");
return len;
}

if (len + sizeof(uint16) > DTLS_CKXEC_LENGTH) {
if (len > max_len) {
memset(&handshake->keyx.psk, 0, sizeof(dtls_handshake_parameters_psk_t));
dtls_warn("the psk identity is too long\n");
dtls_crit("the psk identity is too long\n");
return dtls_alert_fatal_create(DTLS_ALERT_INTERNAL_ERROR);
}
handshake->keyx.psk.id_length = (unsigned int)len;
memcpy(handshake->keyx.psk.identity, p + sizeof(uint16), len);

dtls_int_to_uint16(p, handshake->keyx.psk.id_length);
p += sizeof(uint16);
handshake->keyx.psk.id_length = (uint16_t)len;
memcpy(handshake->keyx.psk.identity, p, len);

memcpy(p, handshake->keyx.psk.identity, handshake->keyx.psk.id_length);
p += handshake->keyx.psk.id_length;
dtls_int_to_uint16(buf, (uint16_t)len);
// p is already at the id in buf + sizeof(uint16)
p += len;

break;
}
Expand All @@ -3032,9 +3030,9 @@ dtls_send_client_key_exchange(dtls_context_t *ctx, dtls_peer_t *peer)
ephemeral_pub_y = p;
p += DTLS_EC_KEY_SIZE;

dtls_ecdsa_generate_key(peer->handshake_params->keyx.ecdsa.own_eph_priv,
ephemeral_pub_x, ephemeral_pub_y,
DTLS_EC_KEY_SIZE);
dtls_ecdsa_generate_key(peer->handshake_params->keyx.ecdsa.own_eph_priv,
ephemeral_pub_x, ephemeral_pub_y,
DTLS_EC_KEY_SIZE);

break;
}
Expand All @@ -3055,7 +3053,7 @@ dtls_send_client_key_exchange(dtls_context_t *ctx, dtls_peer_t *peer)
assert((buf <= p) && ((unsigned int)(p - buf) <= sizeof(buf)));

ret = dtls_send_handshake_msg(ctx, peer, DTLS_HT_CLIENT_KEY_EXCHANGE,
buf, p - buf);
buf, p - buf);

/* Keep hash information for extended master secret */
memcpy(&peer->handshake_params->hs_state.ext_hash,
Expand Down
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