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a541314b1

Brandon P. Enochs

2018-10-27

SUCCESS Duration: 147s

Subject

ntpd: add support for MD5/SHA1 message authentication

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Architecture & Compiler Flags

Architecture: x86_64-linux-gnu Compiler: gcc (Ubuntu 11.4.0-1ubuntu1~22.04.3) 11.4.0

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Commit Diff GitHub →

networking/ntpd.c +241 -25

networking/ntpd.c+241 -25

@@ -62,13 +62,19 @@
	//config: help
	//config: Make ntpd look in /etc/ntp.conf for peers. Only "server address"
	//config: is supported.
+	//config:config FEATURE_NTP_AUTH
+	//config: bool "Support md5/sha1 message authentication codes"
+	//config: default n
+	//config: depends on NTPD

	//applet:IF_NTPD(APPLET(ntpd, BB_DIR_USR_SBIN, BB_SUID_DROP))

	//kbuild:lib-$(CONFIG_NTPD) += ntpd.o

	//usage:#define ntpd_trivial_usage
-	//usage: "[-dnqNw"IF_FEATURE_NTPD_SERVER("l -I IFACE")"] [-S PROG] [-p PEER]..."
+	//usage: "[-dnqNw"IF_FEATURE_NTPD_SERVER("l] [-I IFACE")"] [-S PROG]"
+	//usage: IF_NOT_FEATURE_NTP_AUTH(" [-p PEER]...")
+	//usage: IF_FEATURE_NTP_AUTH(" [-k KEYFILE] [-p [keyno:N:]PEER]...")
	//usage:#define ntpd_full_usage "\n\n"
	//usage: "NTP client/server\n"
	//usage: "\n -d Verbose (may be repeated)"
@@ -76,8 +82,16 @@
	//usage: "\n -q Quit after clock is set"
	//usage: "\n -N Run at high priority"
	//usage: "\n -w Do not set time (only query peers), implies -n"
-	//usage: "\n -S PROG Run PROG after stepping time, stratum change, and every 11 mins"
+	//usage: "\n -S PROG Run PROG after stepping time, stratum change, and every 11 min"
+	//usage: IF_NOT_FEATURE_NTP_AUTH(
	//usage: "\n -p PEER Obtain time from PEER (may be repeated)"
+	//usage: )
+	//usage: IF_FEATURE_NTP_AUTH(
+	//usage: "\n -k FILE Key file (ntp.keys compatible)"
+	//usage: "\n -p [keyno:NUM:]PEER"
+	//usage: "\n Obtain time from PEER (may be repeated)"
+	//usage: "\n Use key NUM for authentication"
+	//usage: )
	//usage: IF_FEATURE_NTPD_CONF(
	//usage: "\n If -p is not given, 'server HOST' lines"
	//usage: "\n from /etc/ntp.conf are used"
@@ -228,14 +242,18 @@
	/* Parameter averaging constant */
	#define AVG 4

+	#define MAX_KEY_NUMBER 65535
+	#define KEYID_SIZE sizeof(uint32_t)

	enum {
	NTP_VERSION = 4,
	NTP_MAXSTRATUM = 15,

-	NTP_DIGESTSIZE = 16,
-	NTP_MSGSIZE_NOAUTH = 48,
-	NTP_MSGSIZE = (NTP_MSGSIZE_NOAUTH + 4 + NTP_DIGESTSIZE),
+	NTP_MD5_DIGESTSIZE = 16,
+	NTP_MSGSIZE_NOAUTH = 48,
+	NTP_MSGSIZE_MD5_AUTH = NTP_MSGSIZE_NOAUTH + KEYID_SIZE + NTP_MD5_DIGESTSIZE,
+	NTP_SHA1_DIGESTSIZE = 20,
+	NTP_MSGSIZE_SHA1_AUTH = NTP_MSGSIZE_NOAUTH + KEYID_SIZE + NTP_SHA1_DIGESTSIZE,

	/* Status Masks */
	MODE_MASK = (7 << 0),
@@ -288,7 +306,7 @@ typedef struct {
	l_fixedpt_t m_rectime;
	l_fixedpt_t m_xmttime;
	uint32_t m_keyid;
-	uint8_t m_digest[NTP_DIGESTSIZE];
+	uint8_t m_digest[ENABLE_FEATURE_NTP_AUTH ? NTP_SHA1_DIGESTSIZE : NTP_MD5_DIGESTSIZE];
	} msg_t;

	typedef struct {
@@ -297,9 +315,26 @@ typedef struct {
	double d_dispersion;
	} datapoint_t;

+	#if ENABLE_FEATURE_NTP_AUTH
+	enum {
+	HASH_MD5,
+	HASH_SHA1,
+	};
+	typedef struct {
+	unsigned id; //try uint16_t?
+	smalluint type;
+	smalluint msg_size;
+	smalluint key_length;
+	char key[0];
+	} key_entry_t;
+	#endif
+
	typedef struct {
	len_and_sockaddr *p_lsa;
	char *p_dotted;
+	#if ENABLE_FEATURE_NTP_AUTH
+	key_entry_t *key_entry;
+	#endif
	int p_fd;
	int datapoint_idx;
	uint32_t lastpkt_refid;
@@ -337,13 +372,14 @@ enum {
	OPT_q = (1 << 1),
	OPT_N = (1 << 2),
	OPT_x = (1 << 3),
+	OPT_k = (1 << 4) * ENABLE_FEATURE_NTP_AUTH,
	/* Insert new options above this line. */
	/* Non-compat options: */
-	OPT_w = (1 << 4),
-	OPT_p = (1 << 5),
-	OPT_S = (1 << 6),
-	OPT_l = (1 << 7) * ENABLE_FEATURE_NTPD_SERVER,
-	OPT_I = (1 << 8) * ENABLE_FEATURE_NTPD_SERVER,
+	OPT_w = (1 << (4+ENABLE_FEATURE_NTP_AUTH)),
+	OPT_p = (1 << (5+ENABLE_FEATURE_NTP_AUTH)),
+	OPT_S = (1 << (6+ENABLE_FEATURE_NTP_AUTH)),
+	OPT_l = (1 << (7+ENABLE_FEATURE_NTP_AUTH)) * ENABLE_FEATURE_NTPD_SERVER,
+	OPT_I = (1 << (8+ENABLE_FEATURE_NTP_AUTH)) * ENABLE_FEATURE_NTPD_SERVER,
	/* We hijack some bits for other purposes */
	OPT_qq = (1 << 31),
	};
@@ -816,8 +852,12 @@ resolve_peer_hostname(peer_t *p)
	return lsa;
	}

+	#if !ENABLE_FEATURE_NTP_AUTH
+	#define add_peers(s, key_entry) \
+	add_peers(s)
+	#endif
	static void
-	add_peers(const char *s)
+	add_peers(const char s, key_entry_t key_entry)
	{
	llist_t *item;
	peer_t *p;
@@ -846,6 +886,7 @@ add_peers(const char *s)
	}
	}

+	IF_FEATURE_NTP_AUTH(p->key_entry = key_entry;)
	llist_add_to(&G.ntp_peers, p);
	G.peer_cnt++;
	}
@@ -870,6 +911,48 @@ do_sendto(int fd,
	return 0;
	}

+	#if ENABLE_FEATURE_NTP_AUTH
+	static void
+	hash(key_entry_t key_entry, const msg_t msg, uint8_t *output)
+	{
+	union {
+	md5_ctx_t m;
+	sha1_ctx_t s;
+	} ctx;
+	unsigned hash_size = sizeof(*msg) - sizeof(msg->m_keyid) - sizeof(msg->m_digest);
+
+	switch (key_entry->type) {
+	case HASH_MD5:
+	md5_begin(&ctx.m);
+	md5_hash(&ctx.m, key_entry->key, key_entry->key_length);
+	md5_hash(&ctx.m, msg, hash_size);
+	md5_end(&ctx.m, output);
+	break;
+	default: /* it's HASH_SHA1 */
+	sha1_begin(&ctx.s);
+	sha1_hash(&ctx.s, key_entry->key, key_entry->key_length);
+	sha1_hash(&ctx.s, msg, hash_size);
+	sha1_end(&ctx.s, output);
+	break;
+	}
+	}
+
+	static void
+	hash_peer(peer_t *p)
+	{
+	p->p_xmt_msg.m_keyid = htonl(p->key_entry->id);
+	hash(p->key_entry, &p->p_xmt_msg, p->p_xmt_msg.m_digest);
+	}
+
+	static int
+	hashes_differ(peer_t p, const msg_t msg)
+	{
+	uint8_t digest[NTP_SHA1_DIGESTSIZE];
+	hash(p->key_entry, msg, digest);
+	return memcmp(digest, msg->m_digest, p->key_entry->msg_size - NTP_MSGSIZE_NOAUTH - KEYID_SIZE);
+	}
+	#endif
+
	static void
	send_query_to_peer(peer_t *p)
	{
@@ -946,9 +1029,18 @@ send_query_to_peer(peer_t *p)
	*/
	p->reachable_bits <<= 1;

+	#if ENABLE_FEATURE_NTP_AUTH
+	if (p->key_entry)
+	hash_peer(p);
	if (do_sendto(p->p_fd, /from:/ NULL, /to:/ &p->p_lsa->u.sa, /addrlen:/ p->p_lsa->len,
-	&p->p_xmt_msg, NTP_MSGSIZE_NOAUTH) == -1
-	) {
+	&p->p_xmt_msg, !p->key_entry ? NTP_MSGSIZE_NOAUTH : p->key_entry->msg_size) == -1
+	)
+	#else
+	if (do_sendto(p->p_fd, /from:/ NULL, /to:/ &p->p_lsa->u.sa, /addrlen:/ p->p_lsa->len,
+	&p->p_xmt_msg, NTP_MSGSIZE_NOAUTH) == -1
+	)
+	#endif
+	{
	close(p->p_fd);
	p->p_fd = -1;
	/*
@@ -1924,10 +2016,21 @@ recv_and_process_peer_pkt(peer_t *p)
	bb_perror_msg_and_die("recv(%s) error", p->p_dotted);
	}

-	if (size != NTP_MSGSIZE_NOAUTH && size != NTP_MSGSIZE) {
+	#if ENABLE_FEATURE_NTP_AUTH
+	if (size != NTP_MSGSIZE_NOAUTH && size != NTP_MSGSIZE_MD5_AUTH && size != NTP_MSGSIZE_SHA1_AUTH) {
+	bb_error_msg("malformed packet received from %s", p->p_dotted);
+	return;
+	}
+	if (p->key_entry && hashes_differ(p, &msg)) {
+	bb_error_msg("invalid cryptographic hash received from %s", p->p_dotted);
+	return;
+	}
+	#else
+	if (size != NTP_MSGSIZE_NOAUTH && size != NTP_MSGSIZE_MD5_AUTH) {
	bb_error_msg("malformed packet received from %s", p->p_dotted);
	return;
	}
+	#endif

	if (msg.m_orgtime.int_partl != p->p_xmt_msg.m_xmttime.int_partl
	\|\| msg.m_orgtime.fractionl != p->p_xmt_msg.m_xmttime.fractionl
@@ -2135,7 +2238,12 @@ recv_and_process_client_pkt(void /int fd/)
	from = xzalloc(to->len);

	size = recv_from_to(G_listen_fd, &msg, sizeof(msg), MSG_DONTWAIT, from, &to->u.sa, to->len);
-	if (size != NTP_MSGSIZE_NOAUTH && size != NTP_MSGSIZE) {
+	#if ENABLE_FEATURE_NTP_AUTH
+	if (size != NTP_MSGSIZE_NOAUTH && size != NTP_MSGSIZE_MD5_AUTH && size != NTP_MSGSIZE_SHA1_AUTH)
+	#else
+	if (size != NTP_MSGSIZE_NOAUTH && size != NTP_MSGSIZE_MD5_AUTH)
+	#endif
+	{
	char *addr;
	if (size < 0) {
	if (errno == EAGAIN)
@@ -2278,6 +2386,19 @@ recv_and_process_client_pkt(void /int fd/)
	* with the -g and -q options. See the tinker command for other options.
	* Note: The kernel time discipline is disabled with this option.
	*/
+	#if ENABLE_FEATURE_NTP_AUTH
+	static key_entry_t *
+	find_key_entry(llist_t *key_entries, unsigned id)
+	{
+	while (key_entries) {
+	key_entry_t cur = (key_entry_t) key_entries->data;
+	if (cur->id == id)
+	return cur;
+	key_entries = key_entries->link;
+	}
+	bb_error_msg_and_die("key %u is not defined", id);
+	}
+	#endif

	/* By doing init in a separate function we decrease stack usage
	* in main loop.
@@ -2286,6 +2407,10 @@ static NOINLINE void ntp_init(char **argv)
	{
	unsigned opts;
	llist_t *peers;
+	#if ENABLE_FEATURE_NTP_AUTH
+	llist_t *key_entries;
+	char *key_file_path;
+	#endif

	srand(getpid());

@@ -2302,8 +2427,10 @@ static NOINLINE void ntp_init(char **argv)

	/* Parse options */
	peers = NULL;
+	IF_FEATURE_NTP_AUTH(key_entries = NULL;)
	opts = getopt32(argv, "^"
	"nqNx" /* compat */
+	IF_FEATURE_NTP_AUTH("k:") /* compat */
	"wp:S:"IF_FEATURE_NTPD_SERVER("l") / NOT compat */
	IF_FEATURE_NTPD_SERVER("I:") /* compat */
	"d" /* compat */
@@ -2311,11 +2438,11 @@ static NOINLINE void ntp_init(char **argv)
	"\0"
	"dd:wn" /* -d: counter; -p: list; -w implies -n */
	IF_FEATURE_NTPD_SERVER(":Il") /* -I implies -l */
-	, &peers, &G.script_name,
-	#if ENABLE_FEATURE_NTPD_SERVER
-	&G.if_name,
-	#endif
-	&G.verbose);
+	IF_FEATURE_NTP_AUTH(, &key_file_path)
+	, &peers, &G.script_name
+	IF_FEATURE_NTPD_SERVER(, &G.if_name)
+	, &G.verbose
+	);

	// if (opts & OPT_x) /* disable stepping, only slew is allowed */
	// G.time_was_stepped = 1;
@@ -2341,19 +2468,107 @@ static NOINLINE void ntp_init(char **argv)
	logmode = LOGMODE_NONE;
	}

+	#if ENABLE_FEATURE_NTP_AUTH
+	if (opts & OPT_k) {
+	char *tokens[4];
+	parser_t *parser;
+
+	parser = config_open(key_file_path);
+	while (config_read(parser, tokens, 4, 3, "# \t", PARSE_NORMAL \| PARSE_MIN_DIE) == 3) {
+	key_entry_t *key_entry;
+	char buffer[40];
+	smalluint hash_type;
+	smalluint msg_size;
+	smalluint key_length;
+	char *key;
+
+	if ((tokens[1][0] \| 0x20) == 'm')
+	/* supports 'M' and 'md5' formats */
+	hash_type = HASH_MD5;
+	else
+	if (strncasecmp(tokens[1], "sha", 3) == 0)
+	/* supports 'sha' and 'sha1' formats */
+	hash_type = HASH_SHA1;
+	else
+	bb_error_msg_and_die("only MD5 and SHA1 keys supported");
+	/* man ntp.keys:
+	* MD5 The key is 1 to 16 printable characters terminated by an EOL,
+	* whitespace, or a # (which is the "start of comment" character).
+	* SHA
+	* SHA1
+	* RMD160 The key is a hex-encoded ASCII string of 40 characters, which
+	* is truncated as necessary.
+	*/
+	key_length = strnlen(tokens[2], sizeof(buffer)+1);
+	if (key_length >= sizeof(buffer)+1) {
+	err:
+	bb_error_msg_and_die("malformed key at line %u", parser->lineno);
+	}
+	if (hash_type == HASH_MD5) {
+	key = tokens[2];
+	msg_size = NTP_MSGSIZE_MD5_AUTH;
+	} else /* it's hash_type == HASH_SHA1 */
+	if (!(key_length & 1)) {
+	key_length >>= 1;
+	if (!hex2bin(buffer, tokens[2], key_length))
+	goto err;
+	key = buffer;
+	msg_size = NTP_MSGSIZE_SHA1_AUTH;
+	} else {
+	goto err;
+	}
+	key_entry = xzalloc(sizeof(*key_entry) + key_length);
+	key_entry->type = hash_type;
+	key_entry->msg_size = msg_size;
+	key_entry->key_length = key_length;
+	memcpy(key_entry->key, key, key_length);
+	key_entry->id = xatou_range(tokens[0], 1, MAX_KEY_NUMBER);
+	llist_add_to(&key_entries, key_entry);
+	}
+	config_close(parser);
+	}
+	#endif
	if (peers) {
+	#if ENABLE_FEATURE_NTP_AUTH
+	while (peers) {
+	char *peer = llist_pop(&peers);
+	key_entry_t *key_entry = NULL;
+	if (strncmp(peer, "keyno:", 6) == 0) {
+	char *end;
+	int key_id;
+	peer += 6;
+	end = strchr(peer, ':');
+	*end = '\0';
+	key_id = xatou_range(peer, 1, MAX_KEY_NUMBER);
+	*end = ':';
+	key_entry = find_key_entry(key_entries, key_id);
+	peer = end + 1;
+	}
+	add_peers(peer, key_entry);
+	}
+	#else
	while (peers)
-	add_peers(llist_pop(&peers));
+	add_peers(llist_pop(&peers), NULL);
+	#endif
	}
	#if ENABLE_FEATURE_NTPD_CONF
	else {
	parser_t *parser;
-	char *token[3];
+	char token[3 + 2ENABLE_FEATURE_NTP_AUTH];

	parser = config_open("/etc/ntp.conf");
-	while (config_read(parser, token, 3, 1, "# \t", PARSE_NORMAL)) {
+	while (config_read(parser, token, 3 + 2*ENABLE_FEATURE_NTP_AUTH, 1, "# \t", PARSE_NORMAL)) {
	if (strcmp(token[0], "server") == 0 && token[1]) {
-	add_peers(token[1]);
+	# if ENABLE_FEATURE_NTP_AUTH
+	key_entry_t *key_entry = NULL;
+	if (token[2] && token[3] && strcmp(token[2], "key") == 0) {
+	unsigned key_id = xatou_range(token[3], 1, MAX_KEY_NUMBER);
+	key_entry = find_key_entry(key_entries, key_id);
+	}
+	add_peers(token[1], key_entry);
+	# else
+	add_peers(token[1], NULL);
+	# endif
	continue;
	}
	bb_error_msg("skipping %s:%u: unimplemented command '%s'",
@@ -2394,6 +2609,7 @@ static NOINLINE void ntp_init(char **argv)
	\| (1 << SIGCHLD)
	, SIG_IGN
	);
+	//TODO: free unused elements of key_entries?
	}

	int ntpd_main(int argc UNUSED_PARAM, char **argv) MAIN_EXTERNALLY_VISIBLE;