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nts: improve NTS-NTP server/client code

Browse source 
Add more comments, assertions, debug messages, and other minor
changes to make the code more robust.
This commit is contained in:
Miroslav Lichvar 2020-07-27 15:38:46 +02:00
parent def137bc80
commit d48f012809
3 changed files with 55 additions and 24 deletions
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9
nts_ntp_auth.c
View file

@ -102,6 +102,10 @@ NNA_GenerateAuthEF(NTP_Packet *packet, NTP_PacketInfo *info, SIV_Instance siv,
body = (unsigned char *)(header + 1);
ciphertext = body + nonce_length + nonce_padding;
if ((unsigned char *)header + auth_length !=
ciphertext + ciphertext_length + ciphertext_padding + additional_padding)
assert(0);
memcpy(body, nonce, nonce_length);
memset(body + nonce_length, 0, nonce_padding);
@ -135,7 +139,7 @@ NNA_DecryptAuthEF(NTP_Packet *packet, NTP_PacketInfo *info, SIV_Instance siv, in
NULL, &ef_type, &ef_body, &ef_body_length))
return 0;
if (ef_type != NTP_EF_NTS_AUTH_AND_EEF)
if (ef_type != NTP_EF_NTS_AUTH_AND_EEF || ef_body_length < sizeof (*header))
return 0;
header = ef_body;
@ -148,7 +152,7 @@ NNA_DecryptAuthEF(NTP_Packet *packet, NTP_PacketInfo *info, SIV_Instance siv, in
return 0;
nonce = (unsigned char *)(header + 1);
ciphertext = (unsigned char *)(header + 1) + get_padded_length(nonce_length);
ciphertext = nonce + get_padded_length(nonce_length);
siv_tag_length = SIV_GetTagLength(siv);
@ -166,6 +170,7 @@ NNA_DecryptAuthEF(NTP_Packet *packet, NTP_PacketInfo *info, SIV_Instance siv, in
}
*plaintext_length = ciphertext_length - siv_tag_length;
assert(*plaintext_length >= 0);
if (!SIV_Decrypt(siv, nonce, nonce_length, packet, ef_start,
ciphertext, ciphertext_length, plaintext, *plaintext_length)) {

44
nts_ntp_client.c
View file

@ -43,8 +43,10 @@
#include "siv.h"
#include "util.h"
/* Maximum length of all cookies to avoid IP fragmentation */
#define MAX_TOTAL_COOKIE_LENGTH (8 * 108)
/* Magic string of files containing keys and cookies */
#define DUMP_IDENTIFIER "NNC0\n"
struct NNC_Instance_Record {
@ -87,6 +89,7 @@ reset_instance(NNC_Instance inst)
memset(&inst->context, 0, sizeof (inst->context));
inst->context_id = 0;
memset(inst->cookies, 0, sizeof (inst->cookies));
inst->num_cookies = 0;
inst->cookie_index = 0;
inst->nak_response = 0;
@ -136,17 +139,15 @@ NNC_DestroyInstance(NNC_Instance inst)
static int
check_cookies(NNC_Instance inst)
{
/* Force NKE if a NAK was received since last valid auth */
if (inst->nak_response && !inst->ok_response && inst->num_cookies > 0) {
/* Force a new NTS-KE session if a NAK was received without a valid response,
or the keys encrypting the cookies need to be refreshed */
if (inst->num_cookies > 0 &&
((inst->nak_response && !inst->ok_response) ||
SCH_GetLastEventMonoTime() - inst->last_nke_success > CNF_GetNtsRefresh())) {
inst->num_cookies = 0;
DEBUG_LOG("Dropped cookies");
}
/* Force NKE if the keys encrypting the cookies are too old */
if (inst->num_cookies > 0 &&
SCH_GetLastEventMonoTime() - inst->last_nke_success > CNF_GetNtsRefresh())
inst->num_cookies = 0;
return inst->num_cookies > 0;
}
@ -203,10 +204,11 @@ get_cookies(NNC_Instance inst)
double now;
int got_data;
assert(!check_cookies(inst));
assert(inst->num_cookies == 0);
now = SCH_GetLastEventMonoTime();
/* Create and start a new NTS-KE session if not already present */
if (!inst->nke) {
if (now < inst->next_nke_attempt) {
DEBUG_LOG("Limiting NTS-KE request rate (%f seconds)",
@ -231,9 +233,13 @@ get_cookies(NNC_Instance inst)
update_next_nke_attempt(inst, now);
/* Wait until the session stops */
if (NKC_IsActive(inst->nke))
return 0;
assert(sizeof (inst->cookies) / sizeof (inst->cookies[0]) == NTS_MAX_COOKIES);
/* Get the new keys, cookies and NTP address if the session was successful */
got_data = NKC_GetNtsData(inst->nke, &inst->context,
inst->cookies, &inst->num_cookies, NTS_MAX_COOKIES,
&ntp_address);
@ -250,17 +256,18 @@ get_cookies(NNC_Instance inst)
inst->context_id++;
/* Force a new session if the NTP address is used by another source, with
an expectation that it will eventually get a non-conflicting address */
if (!set_ntp_address(inst, &ntp_address)) {
inst->num_cookies = 0;
return 0;
}
inst->last_nke_success = now;
inst->cookie_index = 0;
inst->nak_response = 0;
inst->last_nke_success = now;
return 1;
}
@ -269,11 +276,13 @@ get_cookies(NNC_Instance inst)
int
NNC_PrepareForAuth(NNC_Instance inst)
{
/* Try to reload saved keys and cookies (once for the NTS-KE address) */
if (!inst->load_attempt) {
load_cookies(inst);
inst->load_attempt = 1;
}
/* Get new cookies if there are not any, or they are no longer usable */
if (!check_cookies(inst)) {
if (!get_cookies(inst))
return 0;
@ -288,8 +297,9 @@ NNC_PrepareForAuth(NNC_Instance inst)
return 0;
}
UTI_GetRandomBytes(&inst->uniq_id, sizeof (inst->uniq_id));
UTI_GetRandomBytes(&inst->nonce, sizeof (inst->nonce));
/* Prepare data for NNC_GenerateRequestAuth() */
UTI_GetRandomBytes(inst->uniq_id, sizeof (inst->uniq_id));
UTI_GetRandomBytes(inst->nonce, sizeof (inst->nonce));
return 1;
}
@ -315,7 +325,7 @@ NNC_GenerateRequestAuth(NNC_Instance inst, NTP_Packet *packet,
MAX_TOTAL_COOKIE_LENGTH / (cookie->length + 4));
if (!NEF_AddField(packet, info, NTP_EF_NTS_UNIQUE_IDENTIFIER,
&inst->uniq_id, sizeof (inst->uniq_id)))
inst->uniq_id, sizeof (inst->uniq_id)))
return 0;
if (!NEF_AddField(packet, info, NTP_EF_NTS_COOKIE,
@ -372,6 +382,9 @@ extract_cookies(NNC_Instance inst, unsigned char *plaintext, int length)
continue;
index = (inst->cookie_index + inst->num_cookies) % NTS_MAX_COOKIES;
assert(index >= 0 && index < NTS_MAX_COOKIES);
assert(sizeof (inst->cookies) / sizeof (inst->cookies[0]) == NTS_MAX_COOKIES);
memcpy(inst->cookies[index].cookie, ef_body, ef_body_length);
inst->cookies[index].length = ef_body_length;
inst->num_cookies++;
@ -398,7 +411,7 @@ NNC_CheckResponseAuth(NNC_Instance inst, NTP_Packet *packet,
if (info->ext_fields == 0 || info->mode != MODE_SERVER)
return 0;
/* Accept only one response per request */
/* Accept at most one response per request */
if (inst->ok_response)
return 0;
@ -411,7 +424,8 @@ NNC_CheckResponseAuth(NNC_Instance inst, NTP_Packet *packet,
for (parsed = NTP_HEADER_LENGTH; parsed < info->length; parsed += ef_length) {
if (!NEF_ParseField(packet, info->length, parsed,
&ef_length, &ef_type, &ef_body, &ef_body_length))
break;
/* This is not expected as the packet already passed NAU_ParsePacket() */
return 0;
switch (ef_type) {
case NTP_EF_NTS_UNIQUE_IDENTIFIER:

26
nts_ntp_server.c
View file

@ -112,15 +112,18 @@ NNS_CheckRequestAuth(NTP_Packet *packet, NTP_PacketInfo *info, uint32_t *kod)
for (parsed = NTP_HEADER_LENGTH; parsed < info->length; parsed += ef_length) {
if (!NEF_ParseField(packet, info->length, parsed,
&ef_length, &ef_type, &ef_body, &ef_body_length))
break;
/* This is not expected as the packet already passed NAU_ParsePacket() */
return 0;
switch (ef_type) {
case NTP_EF_NTS_UNIQUE_IDENTIFIER:
has_uniq_id = 1;
break;
case NTP_EF_NTS_COOKIE:
if (has_cookie || ef_body_length > sizeof (cookie.cookie))
if (has_cookie || ef_body_length > sizeof (cookie.cookie)) {
DEBUG_LOG("Unexpected cookie/length");
return 0;
}
cookie.length = ef_body_length;
memcpy(cookie.cookie, ef_body, ef_body_length);
has_cookie = 1;
@ -199,13 +202,18 @@ NNS_CheckRequestAuth(NTP_Packet *packet, NTP_PacketInfo *info, uint32_t *kod)
return 0;
}
/* Prepare data for NNS_GenerateResponseAuth() to minimise the time spent
there (when the TX timestamp is already set) */
UTI_GetRandomBytes(server->nonce, sizeof (server->nonce));
server->num_cookies = MIN(NTS_MAX_COOKIES, requested_cookies);
for (i = 0; i < server->num_cookies; i++)
assert(sizeof (server->cookies) / sizeof (server->cookies[0]) == NTS_MAX_COOKIES);
for (i = 0; i < NTS_MAX_COOKIES && i < requested_cookies; i++)
if (!NKS_GenerateCookie(&context, &server->cookies[i]))
return 0;
server->num_cookies = i;
return 1;
}
@ -224,14 +232,16 @@ NNS_GenerateResponseAuth(NTP_Packet *request, NTP_PacketInfo *req_info,
if (!server || req_info->mode != MODE_CLIENT || res_info->mode != MODE_SERVER)
return 0;
/* Make sure this is a response to the expected request */
/* Make sure this is a response to the request from the last call
of NNS_CheckRequestAuth() */
if (UTI_CompareNtp64(&server->req_tx, &request->transmit_ts) != 0)
assert(0);
for (parsed = NTP_HEADER_LENGTH; parsed < req_info->length; parsed += ef_length) {
if (!NEF_ParseField(request, req_info->length, parsed,
&ef_length, &ef_type, &ef_body, &ef_body_length))
break;
/* This is not expected as the packet already passed NAU_ParsePacket() */
return 0;
switch (ef_type) {
case NTP_EF_NTS_UNIQUE_IDENTIFIER:
@ -249,7 +259,7 @@ NNS_GenerateResponseAuth(NTP_Packet *request, NTP_PacketInfo *req_info,
for (i = 0, plaintext_length = 0; i < server->num_cookies; i++) {
if (!NEF_SetField(plaintext, sizeof (plaintext), plaintext_length,
NTP_EF_NTS_COOKIE, &server->cookies[i].cookie,
NTP_EF_NTS_COOKIE, server->cookies[i].cookie,
server->cookies[i].length, &ef_length))
return 0;
@ -259,6 +269,8 @@ NNS_GenerateResponseAuth(NTP_Packet *request, NTP_PacketInfo *req_info,
server->num_cookies = 0;
/* Generate an authenticator field which will make the length
of the response equal to the length of the request */
if (!NNA_GenerateAuthEF(response, res_info, server->siv,
server->nonce, sizeof (server->nonce),
plaintext, plaintext_length,