Head

GCC Code Coverage Report

Directory:	./		Exec	Total	Coverage
File:	usr.sbin/snmpd/usm.c	Lines:	26	309	8.4 %
Date:	2017-11-13	Branches:	18	161	11.2 %


/*	$OpenBSD: usm.c,v 1.11 2016/10/28 08:01:53 rzalamena Exp $	*/

/*
 * Copyright (c) 2012 GeNUA mbH
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <sys/queue.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <sys/tree.h>

#include <net/if.h>

#include <errno.h>
#include <event.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <signal.h>
#ifdef DEBUG
#include <assert.h>
#endif

#include <openssl/evp.h>
#include <openssl/hmac.h>

#include "snmpd.h"
#include "mib.h"

SLIST_HEAD(, usmuser)	usmuserlist;

const EVP_MD		*usm_get_md(enum usmauth);
const EVP_CIPHER	*usm_get_cipher(enum usmpriv);
void			 usm_cb_digest(void *, size_t);
int			 usm_valid_digest(struct snmp_message *, off_t, char *,
			    size_t);
struct ber_element	*usm_decrypt(struct snmp_message *,
			    struct ber_element *);
ssize_t			 usm_crypt(struct snmp_message *, u_char *, int,
			    u_char *, int);
char			*usm_passwd2key(const EVP_MD *, char *, int *);

void
usm_generate_keys(void)
{
	struct usmuser	*up;
	const EVP_MD	*md;
	char		*key;
	int		 len;

	SLIST_FOREACH(up, &usmuserlist, uu_next) {
		if ((md = usm_get_md(up->uu_auth)) == NULL)
			continue;

		/* convert auth password to key */
		len = 0;
		key = usm_passwd2key(md, up->uu_authkey, &len);
		free(up->uu_authkey);
		up->uu_authkey = key;
		up->uu_authkeylen = len;

		/* optionally convert privacy password to key */
		if (up->uu_priv != PRIV_NONE) {
			arc4random_buf(&up->uu_salt, sizeof(up->uu_salt));

			len = SNMP_CIPHER_KEYLEN;
			key = usm_passwd2key(md, up->uu_privkey, &len);
			free(up->uu_privkey);
			up->uu_privkey = key;
		}
	}
	return;
}

const EVP_MD *
usm_get_md(enum usmauth ua)
{
	switch (ua) {
	case AUTH_MD5:
		return EVP_md5();
	case AUTH_SHA1:
		return EVP_sha1();
	case AUTH_NONE:
	default:
		return NULL;
	}
}

const EVP_CIPHER *
usm_get_cipher(enum usmpriv up)
{
	switch (up) {
	case PRIV_DES:
		return EVP_des_cbc();
	case PRIV_AES:
		return EVP_aes_128_cfb128();
	case PRIV_NONE:
	default:
		return NULL;
	}
}

struct usmuser *
usm_newuser(char *name, const char **errp)
{
	struct usmuser *up = usm_finduser(name);
	if (up != NULL) {
		*errp = "user redefined";
		return NULL;
	}
	if ((up = calloc(1, sizeof(*up))) == NULL)
		fatal("usm");
	up->uu_name = name;
	SLIST_INSERT_HEAD(&usmuserlist, up, uu_next);
	return up;
}

struct usmuser *
usm_finduser(char *name)
{
	struct usmuser *up;

	SLIST_FOREACH(up, &usmuserlist, uu_next) {
		if (!strcmp(up->uu_name, name))
			return up;
	}
	return NULL;
}

int
usm_checkuser(struct usmuser *up, const char **errp)
{
	char	*auth = NULL, *priv = NULL;

	if (up->uu_auth != AUTH_NONE && up->uu_authkey == NULL) {
		*errp = "missing auth passphrase";
		goto fail;
	} else if (up->uu_auth == AUTH_NONE && up->uu_authkey != NULL)
		up->uu_auth = AUTH_DEFAULT;

	if (up->uu_priv != PRIV_NONE && up->uu_privkey == NULL) {
		*errp = "missing priv passphrase";
		goto fail;
	} else if (up->uu_priv == PRIV_NONE && up->uu_privkey != NULL)
		up->uu_priv = PRIV_DEFAULT;

	if (up->uu_auth == AUTH_NONE && up->uu_priv != PRIV_NONE) {
		/* Standard prohibits noAuthPriv */
		*errp = "auth is mandatory with enc";
		goto fail;
	}

	switch (up->uu_auth) {
	case AUTH_NONE:
		auth = "none";
		break;
	case AUTH_MD5:
		up->uu_seclevel |= SNMP_MSGFLAG_AUTH;
		auth = "HMAC-MD5-96";
		break;
	case AUTH_SHA1:
		up->uu_seclevel |= SNMP_MSGFLAG_AUTH;
		auth = "HMAC-SHA1-96";
		break;
	}

	switch (up->uu_priv) {
	case PRIV_NONE:
		priv = "none";
		break;
	case PRIV_DES:
		up->uu_seclevel |= SNMP_MSGFLAG_PRIV;
		priv = "CBC-DES";
		break;
	case PRIV_AES:
		up->uu_seclevel |= SNMP_MSGFLAG_PRIV;
		priv = "CFB128-AES-128";
		break;
	}

	log_debug("user \"%s\" auth %s enc %s", up->uu_name, auth, priv);
	return 0;

fail:
	free(up->uu_name);
	free(up->uu_authkey);
	free(up->uu_privkey);
	SLIST_REMOVE(&usmuserlist, up, usmuser, uu_next);
	free(up);
	return -1;
}

struct ber_element *
usm_decode(struct snmp_message *msg, struct ber_element *elm, const char **errp)
{
	struct snmp_stats	*stats = &snmpd_env->sc_stats;
	off_t			 offs, offs2;
	char			*usmparams;
	size_t			 len;
	size_t			 enginelen, userlen, digestlen, saltlen;
	struct ber		 ber;
	struct ber_element	*usm = NULL, *next = NULL, *decr;
	char			*engineid;
	char			*user;
	char			*digest, *salt;
	u_long			 now;
	long long		 engine_boots, engine_time;

	bzero(&ber, sizeof(ber));
	offs = ber_getpos(elm);

	if (ber_get_nstring(elm, (void *)&usmparams, &len) < 0) {
		*errp = "cannot decode security params";
		goto done;
	}

	ber.fd = -1;
	ber_set_readbuf(&ber, usmparams, len);
	usm = ber_read_elements(&ber, NULL);
	if (usm == NULL) {
		*errp = "cannot decode security params";
		goto done;
	}

#ifdef DEBUG
	fprintf(stderr, "decode USM parameters:\n");
	smi_debug_elements(usm);
#endif

	if (ber_scanf_elements(usm, "{xiixpxx", &engineid, &enginelen,
	    &engine_boots, &engine_time, &user, &userlen, &offs2,
	    &digest, &digestlen, &salt, &saltlen) != 0) {
		*errp = "cannot decode USM params";
		goto done;
	}

	log_debug("USM: engineid '%s', engine boots %lld, engine time %lld, "
	    "user '%s'", tohexstr(engineid, enginelen), engine_boots,
	    engine_time, user);

	if (enginelen > SNMPD_MAXENGINEIDLEN ||
	    userlen > SNMPD_MAXUSERNAMELEN ||
	    (digestlen != (MSG_HAS_AUTH(msg) ? SNMP_USM_DIGESTLEN : 0)) ||
	    (saltlen != (MSG_HAS_PRIV(msg) ? SNMP_USM_SALTLEN : 0))) {
		*errp = "bad field length";
		goto done;
	}

	if (enginelen != snmpd_env->sc_engineid_len ||
	    memcmp(engineid, snmpd_env->sc_engineid, enginelen) != 0) {
		*errp = "unknown engine id";
		msg->sm_usmerr = OIDVAL_usmErrEngineId;
		stats->snmp_usmnosuchengine++;
		goto done;
	}

	if (engine_boots != 0LL && engine_time != 0LL) {
		now = snmpd_engine_time();
		if (engine_boots != snmpd_env->sc_engine_boots ||
		    engine_time < (long long)(now - SNMP_MAX_TIMEWINDOW) ||
		    engine_time > (long long)(now + SNMP_MAX_TIMEWINDOW)) {
			*errp = "out of time window";
			msg->sm_usmerr = OIDVAL_usmErrTimeWindow;
			stats->snmp_usmtimewindow++;
			goto done;
		}
	}

	msg->sm_engine_boots = (u_int32_t)engine_boots;
	msg->sm_engine_time = (u_int32_t)engine_time;

	memcpy(msg->sm_username, user, userlen);
	msg->sm_username[userlen] = '\0';
	msg->sm_user = usm_finduser(msg->sm_username);
	if (msg->sm_user == NULL) {
		*errp = "no such user";
		msg->sm_usmerr = OIDVAL_usmErrUserName;
		stats->snmp_usmnosuchuser++;
		goto done;
	}
	if (MSG_SECLEVEL(msg) > msg->sm_user->uu_seclevel) {
		*errp = "unsupported security model";
		msg->sm_usmerr = OIDVAL_usmErrSecLevel;
		stats->snmp_usmbadseclevel++;
		goto done;
	}

	/*
	 * offs is the offset of the USM string within the serialized msg
	 * and offs2 the offset of the digest within the USM string.
	 */
	if (!usm_valid_digest(msg, offs + offs2, digest, digestlen)) {
		*errp = "bad msg digest";
		msg->sm_usmerr = OIDVAL_usmErrDigest;
		stats->snmp_usmwrongdigest++;
		goto done;
	}

	if (MSG_HAS_PRIV(msg)) {
		memcpy(msg->sm_salt, salt, saltlen);
		if ((decr = usm_decrypt(msg, elm->be_next)) == NULL) {
			*errp = "cannot decrypt msg";
			msg->sm_usmerr = OIDVAL_usmErrDecrypt;
			stats->snmp_usmdecrypterr++;
			goto done;
		}
		ber_replace_elements(elm, decr);
	}
	next = elm->be_next;

done:
	ber_free(&ber);
	if (usm != NULL)
		ber_free_elements(usm);
	return next;
}

struct ber_element *
usm_encode(struct snmp_message *msg, struct ber_element *e)
{
	struct ber		 ber;
	struct ber_element	*usm, *a, *res = NULL;
	void			*ptr;
	char			 digest[SNMP_USM_DIGESTLEN];
	size_t			 digestlen, saltlen, len;

	msg->sm_digest_offs = 0;
	bzero(&ber, sizeof(ber));
	ber.fd = -1;

	usm = ber_add_sequence(NULL);

	if (MSG_HAS_AUTH(msg)) {
		/*
		 * Fill in enough zeroes and remember the position within the
		 * messages. The digest will be calculated once the message
		 * is complete.
		 */
#ifdef DEBUG
		assert(msg->sm_user != NULL);
#endif
		bzero(digest, sizeof(digest));
		digestlen = sizeof(digest);
	} else
		digestlen = 0;

	if (MSG_HAS_PRIV(msg)) {
#ifdef DEBUG
		assert(msg->sm_user != NULL);
#endif
		++(msg->sm_user->uu_salt);
		memcpy(msg->sm_salt, &msg->sm_user->uu_salt,
		    sizeof(msg->sm_salt));
		saltlen = sizeof(msg->sm_salt);
	} else
		saltlen = 0;

	msg->sm_engine_boots = (u_int32_t)snmpd_env->sc_engine_boots;
	msg->sm_engine_time = (u_int32_t)snmpd_engine_time();
	if ((a = ber_printf_elements(usm, "xdds",
	    snmpd_env->sc_engineid, snmpd_env->sc_engineid_len,
	    msg->sm_engine_boots, msg->sm_engine_time,
	    msg->sm_username)) == NULL)
		goto done;

	if ((a = ber_add_nstring(a, digest, digestlen)) == NULL)
		goto done;
	if (digestlen > 0)
		ber_set_writecallback(a, usm_cb_digest, msg);

	if ((a = ber_add_nstring(a, msg->sm_salt, saltlen)) == NULL)
		goto done;

#ifdef DEBUG
	fprintf(stderr, "encode USM parameters:\n");
	smi_debug_elements(usm);
#endif
	len = ber_write_elements(&ber, usm);
	if (ber_get_writebuf(&ber, &ptr) > 0) {
		res = ber_add_nstring(e, (char *)ptr, len);
		if (digestlen > 0)
			ber_set_writecallback(res, usm_cb_digest, msg);
	}

done:
	ber_free(&ber);
	ber_free_elements(usm);
	return res;
}

void
usm_cb_digest(void *arg, size_t offs)
{
	struct snmp_message *msg = arg;
	msg->sm_digest_offs += offs;
}

struct ber_element *
usm_encrypt(struct snmp_message *msg, struct ber_element *pdu)
{
	struct ber		 ber;
	struct ber_element	*encrpdu = NULL;
	void			*ptr;
	int			 len;
	ssize_t			 elen;
	u_char			 encbuf[READ_BUF_SIZE];

	if (!MSG_HAS_PRIV(msg))
		return pdu;

	bzero(&ber, sizeof(ber));
	ber.fd = -1;

#ifdef DEBUG
	fprintf(stderr, "encrypted PDU:\n");
	smi_debug_elements(pdu);
#endif

	len = ber_write_elements(&ber, pdu);
	if (ber_get_writebuf(&ber, &ptr) > 0) {
		elen = usm_crypt(msg, ptr, len, encbuf, 1);
		if (elen > 0)
			encrpdu = ber_add_nstring(NULL, (char *)encbuf, elen);
	}

	ber_free(&ber);
	ber_free_elements(pdu);
	return encrpdu;
}

/*
 * Calculate message digest and replace within message
 */
void
usm_finalize_digest(struct snmp_message *msg, char *buf, ssize_t len)
{
	const EVP_MD	*md;
	u_char		 digest[EVP_MAX_MD_SIZE];
	unsigned	 hlen;

	if (msg->sm_resp == NULL ||
	    !MSG_HAS_AUTH(msg) ||
	    msg->sm_user == NULL ||
	    msg->sm_digest_offs == 0 ||
	    len <= 0)
		return;
	bzero(digest, SNMP_USM_DIGESTLEN);
#ifdef DEBUG
	assert(msg->sm_digest_offs + SNMP_USM_DIGESTLEN <= (size_t)len);
	assert(!memcmp(buf + msg->sm_digest_offs, digest, SNMP_USM_DIGESTLEN));
#endif

	if ((md = usm_get_md(msg->sm_user->uu_auth)) == NULL)
		return;

	HMAC(md, msg->sm_user->uu_authkey, (int)msg->sm_user->uu_authkeylen,
	    (u_char*)buf, (size_t)len, digest, &hlen);

	memcpy(buf + msg->sm_digest_offs, digest, SNMP_USM_DIGESTLEN);
	return;
}

void
usm_make_report(struct snmp_message *msg)
{
	struct ber_oid		 usmstat = OID(MIB_usmStats, 0, 0);

	/* Always send report in clear-text */
	msg->sm_flags = 0;
	msg->sm_context = SNMP_C_REPORT;
	msg->sm_username[0] = '\0';
	usmstat.bo_id[OIDIDX_usmStats] = msg->sm_usmerr;
	usmstat.bo_n = OIDIDX_usmStats + 2;
	if (msg->sm_varbindresp != NULL)
		ber_free_elements(msg->sm_varbindresp);
	msg->sm_varbindresp = ber_add_sequence(NULL);
	mps_getreq(NULL, msg->sm_varbindresp, &usmstat, msg->sm_version);
	return;
}

int
usm_valid_digest(struct snmp_message *msg, off_t offs,
	char *digest, size_t digestlen)
{
	const EVP_MD	*md;
	u_char		 exp_digest[EVP_MAX_MD_SIZE];
	unsigned	 hlen;

	if (!MSG_HAS_AUTH(msg))
		return 1;

	if (digestlen != SNMP_USM_DIGESTLEN)
		return 0;

#ifdef DEBUG
	assert(offs + digestlen <= msg->sm_datalen);
	assert(bcmp(&msg->sm_data[offs], digest, digestlen) == 0);
#endif

	if ((md = usm_get_md(msg->sm_user->uu_auth)) == NULL)
		return 0;

	memset(&msg->sm_data[offs], 0, digestlen);
	HMAC(md, msg->sm_user->uu_authkey, (int)msg->sm_user->uu_authkeylen,
	    msg->sm_data, msg->sm_datalen, exp_digest, &hlen);
	/* we don't bother to restore the original message */

	if (hlen < digestlen)
		return 0;

	return memcmp(digest, exp_digest, digestlen) == 0;
}

struct ber_element *
usm_decrypt(struct snmp_message *msg, struct ber_element *encr)
{
	u_char			*privstr;
	size_t			 privlen;
	u_char			 buf[READ_BUF_SIZE];
	struct ber		 ber;
	struct ber_element	*scoped_pdu = NULL;
	ssize_t			 scoped_pdu_len;

	if (ber_get_nstring(encr, (void *)&privstr, &privlen) < 0)
		return NULL;

	scoped_pdu_len = usm_crypt(msg, privstr, (int)privlen, buf, 0);
	if (scoped_pdu_len < 0)
		return NULL;

	bzero(&ber, sizeof(ber));
	ber.fd = -1;
	ber_set_readbuf(&ber, buf, scoped_pdu_len);
	scoped_pdu = ber_read_elements(&ber, NULL);

#ifdef DEBUG
	if (scoped_pdu != NULL) {
		fprintf(stderr, "decrypted scoped PDU:\n");
		smi_debug_elements(scoped_pdu);
	}
#endif

	ber_free(&ber);
	return scoped_pdu;
}

ssize_t
usm_crypt(struct snmp_message *msg, u_char *inbuf, int inlen, u_char *outbuf,
	int do_encrypt)
{
	const EVP_CIPHER	*cipher;
	EVP_CIPHER_CTX		 ctx;
	u_char			*privkey;
	int			 i;
	u_char			 iv[EVP_MAX_IV_LENGTH];
	int			 len, len2;
	int			 rv;
	u_int32_t		 ivv;

	if ((cipher = usm_get_cipher(msg->sm_user->uu_priv)) == NULL)
		return -1;

	privkey = (u_char *)msg->sm_user->uu_privkey;
#ifdef DEBUG
	assert(privkey != NULL);
#endif
	switch (msg->sm_user->uu_priv) {
	case PRIV_DES:
		/* RFC3414, chap 8.1.1.1. */
		for (i = 0; i < 8; i++)
			iv[i] = msg->sm_salt[i] ^ privkey[SNMP_USM_SALTLEN + i];
		break;
	case PRIV_AES:
		/* RFC3826, chap 3.1.2.1. */
		ivv = htobe32(msg->sm_engine_boots);
		memcpy(iv, &ivv, sizeof(ivv));
		ivv = htobe32(msg->sm_engine_time);
		memcpy(iv + sizeof(ivv), &ivv, sizeof(ivv));
		memcpy(iv + 2 * sizeof(ivv), msg->sm_salt, SNMP_USM_SALTLEN);
		break;
	default:
		return -1;
	}

	if (!EVP_CipherInit(&ctx, cipher, privkey, iv, do_encrypt))
		return -1;

	if (!do_encrypt)
		EVP_CIPHER_CTX_set_padding(&ctx, 0);

	if (EVP_CipherUpdate(&ctx, outbuf, &len, inbuf, inlen) &&
	    EVP_CipherFinal_ex(&ctx, outbuf + len, &len2))
		rv = len + len2;
	else
		rv = -1;

	EVP_CIPHER_CTX_cleanup(&ctx);
	return rv;
}

/*
 * RFC3414, Password to Key Algorithm
 */
char *
usm_passwd2key(const EVP_MD *md, char *passwd, int *maxlen)
{
	EVP_MD_CTX	 ctx;
	int		 i, count;
	u_char		*pw, *c;
	u_char		 pwbuf[2 * EVP_MAX_MD_SIZE + SNMPD_MAXENGINEIDLEN];
	u_char		 keybuf[EVP_MAX_MD_SIZE];
	unsigned	 dlen;
	char		*key;

	EVP_DigestInit(&ctx, md);
	pw = (u_char *)passwd;
	for (count = 0; count < 1048576; count += 64) {
		c = pwbuf;
		for (i = 0; i < 64; i++) {
			if (*pw == '\0')
				pw = (u_char *)passwd;
			*c++ = *pw++;
		}
		EVP_DigestUpdate(&ctx, pwbuf, 64);
	}
	EVP_DigestFinal(&ctx, keybuf, &dlen);
	EVP_MD_CTX_cleanup(&ctx);

	/* Localize the key */
#ifdef DEBUG
	assert(snmpd_env->sc_engineid_len <= SNMPD_MAXENGINEIDLEN);
#endif
	memcpy(pwbuf, keybuf, dlen);
	memcpy(pwbuf + dlen, snmpd_env->sc_engineid,
	    snmpd_env->sc_engineid_len);
	memcpy(pwbuf + dlen + snmpd_env->sc_engineid_len, keybuf, dlen);

	EVP_DigestInit(&ctx, md);
	EVP_DigestUpdate(&ctx, pwbuf, 2 * dlen + snmpd_env->sc_engineid_len);
	EVP_DigestFinal(&ctx, keybuf, &dlen);
	EVP_MD_CTX_cleanup(&ctx);

	if (*maxlen > 0 && dlen > (unsigned)*maxlen)
		dlen = (unsigned)*maxlen;
	if ((key = malloc(dlen)) == NULL)
		fatal("key");
	memcpy(key, keybuf, dlen);
	*maxlen = (int)dlen;
	return key;
}


Generated by: GCOVR (Version 3.3)

Line	Branch	Exec	Source
1			/* $OpenBSD: usm.c,v 1.11 2016/10/28 08:01:53 rzalamena Exp $ */
2
3			/*
4			* Copyright (c) 2012 GeNUA mbH
5			*
6			* Permission to use, copy, modify, and distribute this software for any
7			* purpose with or without fee is hereby granted, provided that the above
8			* copyright notice and this permission notice appear in all copies.
9			*
10			* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
11			* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
12			* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
13			* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
14			* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
15			* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
16			* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
17			*/
18
19			#include <sys/queue.h>
20			#include <sys/types.h>
21			#include <sys/stat.h>
22			#include <sys/socket.h>
23			#include <sys/un.h>
24			#include <sys/tree.h>
25
26			#include <net/if.h>
27
28			#include <errno.h>
29			#include <event.h>
30			#include <fcntl.h>
31			#include <stdlib.h>
32			#include <string.h>
33			#include <unistd.h>
34			#include <signal.h>
35			#ifdef DEBUG
36			#include <assert.h>
37			#endif
38
39			#include <openssl/evp.h>
40			#include <openssl/hmac.h>
41
42			#include "snmpd.h"
43			#include "mib.h"
44
45			SLIST_HEAD(, usmuser) usmuserlist;
46
47			const EVP_MD *usm_get_md(enum usmauth);
48			const EVP_CIPHER *usm_get_cipher(enum usmpriv);
49			void usm_cb_digest(void *, size_t);
50			int usm_valid_digest(struct snmp_message , off_t, char ,
51			size_t);
52			struct ber_element usm_decrypt(struct snmp_message ,
53			struct ber_element *);
54			ssize_t usm_crypt(struct snmp_message , u_char , int,
55			u_char *, int);
56			char usm_passwd2key(const EVP_MD , char , int );
57
58			void
59			usm_generate_keys(void)
60			{
61			struct usmuser *up;
62			const EVP_MD *md;
63			char *key;
64			int len;
65
66			SLIST_FOREACH(up, &usmuserlist, uu_next) {
67			if ((md = usm_get_md(up->uu_auth)) == NULL)
68			continue;
69
70			/* convert auth password to key */
71			len = 0;
72			key = usm_passwd2key(md, up->uu_authkey, &len);
73			free(up->uu_authkey);
74			up->uu_authkey = key;
75			up->uu_authkeylen = len;
76
77			/* optionally convert privacy password to key */
78			if (up->uu_priv != PRIV_NONE) {
79			arc4random_buf(&up->uu_salt, sizeof(up->uu_salt));
80
81			len = SNMP_CIPHER_KEYLEN;
82			key = usm_passwd2key(md, up->uu_privkey, &len);
83			free(up->uu_privkey);
84			up->uu_privkey = key;
85			}
86			}
87			return;
88			}
89
90			const EVP_MD *
91			usm_get_md(enum usmauth ua)
92			{
93			switch (ua) {
94			case AUTH_MD5:
95			return EVP_md5();
96			case AUTH_SHA1:
97			return EVP_sha1();
98			case AUTH_NONE:
99			default:
100			return NULL;
101			}
102			}
103
104			const EVP_CIPHER *
105			usm_get_cipher(enum usmpriv up)
106			{
107			switch (up) {
108			case PRIV_DES:
109			return EVP_des_cbc();
110			case PRIV_AES:
111			return EVP_aes_128_cfb128();
112			case PRIV_NONE:
113			default:
114			return NULL;
115			}
116			}
117
118			struct usmuser *
119			usm_newuser(char name, const char *errp)
120			{
121		16	struct usmuser *up = usm_finduser(name);
122	✗✓	8	if (up != NULL) {
123			*errp = "user redefined";
124			return NULL;
125			}
126	✗✓	8	if ((up = calloc(1, sizeof(*up))) == NULL)
127			fatal("usm");
128		8	up->uu_name = name;
129		8	SLIST_INSERT_HEAD(&usmuserlist, up, uu_next);
130		8	return up;
131		8	}
132
133			struct usmuser *
134			usm_finduser(char *name)
135			{
136			struct usmuser *up;
137
138	✗✓	24	SLIST_FOREACH(up, &usmuserlist, uu_next) {
139			if (!strcmp(up->uu_name, name))
140			return up;
141			}
142		8	return NULL;
143		8	}
144
145			int
146			usm_checkuser(struct usmuser up, const char *errp)
147			{
148			char auth = NULL, priv = NULL;
149
150	✗✓✗✗	16	if (up->uu_auth != AUTH_NONE && up->uu_authkey == NULL) {
151			*errp = "missing auth passphrase";
152			goto fail;
153	✓✗✓✗	16	} else if (up->uu_auth == AUTH_NONE && up->uu_authkey != NULL)
154		8	up->uu_auth = AUTH_DEFAULT;
155
156	✓✓✗✓	12	if (up->uu_priv != PRIV_NONE && up->uu_privkey == NULL) {
157			*errp = "missing priv passphrase";
158			goto fail;
159	✓✓✗✓	12	} else if (up->uu_priv == PRIV_NONE && up->uu_privkey != NULL)
160			up->uu_priv = PRIV_DEFAULT;
161
162	✗✓✗✗	8	if (up->uu_auth == AUTH_NONE && up->uu_priv != PRIV_NONE) {
163			/* Standard prohibits noAuthPriv */
164			*errp = "auth is mandatory with enc";
165			goto fail;
166			}
167
168	✗✗✓✓	16	switch (up->uu_auth) {
169			case AUTH_NONE:
170			auth = "none";
171			break;
172			case AUTH_MD5:
173			up->uu_seclevel \|= SNMP_MSGFLAG_AUTH;
174			auth = "HMAC-MD5-96";
175			break;
176			case AUTH_SHA1:
177		8	up->uu_seclevel \|= SNMP_MSGFLAG_AUTH;
178			auth = "HMAC-SHA1-96";
179		8	break;
180			}
181
182	✓✗✓✓	16	switch (up->uu_priv) {
183			case PRIV_NONE:
184			priv = "none";
185		4	break;
186			case PRIV_DES:
187			up->uu_seclevel \|= SNMP_MSGFLAG_PRIV;
188			priv = "CBC-DES";
189			break;
190			case PRIV_AES:
191		4	up->uu_seclevel \|= SNMP_MSGFLAG_PRIV;
192			priv = "CFB128-AES-128";
193		4	break;
194			}
195
196		8	log_debug("user \"%s\" auth %s enc %s", up->uu_name, auth, priv);
197		8	return 0;
198
199			fail:
200			free(up->uu_name);
201			free(up->uu_authkey);
202			free(up->uu_privkey);
203			SLIST_REMOVE(&usmuserlist, up, usmuser, uu_next);
204			free(up);
205			return -1;
206		8	}
207
208			struct ber_element *
209			usm_decode(struct snmp_message msg, struct ber_element elm, const char **errp)
210			{
211			struct snmp_stats *stats = &snmpd_env->sc_stats;
212			off_t offs, offs2;
213			char *usmparams;
214			size_t len;
215			size_t enginelen, userlen, digestlen, saltlen;
216			struct ber ber;
217			struct ber_element usm = NULL, next = NULL, *decr;
218			char *engineid;
219			char *user;
220			char digest, salt;
221			u_long now;
222			long long engine_boots, engine_time;
223
224			bzero(&ber, sizeof(ber));
225			offs = ber_getpos(elm);
226
227			if (ber_get_nstring(elm, (void *)&usmparams, &len) < 0) {
228			*errp = "cannot decode security params";
229			goto done;
230			}
231
232			ber.fd = -1;
233			ber_set_readbuf(&ber, usmparams, len);
234			usm = ber_read_elements(&ber, NULL);
235			if (usm == NULL) {
236			*errp = "cannot decode security params";
237			goto done;
238			}
239
240			#ifdef DEBUG
241			fprintf(stderr, "decode USM parameters:\n");
242			smi_debug_elements(usm);
243			#endif
244
245			if (ber_scanf_elements(usm, "{xiixpxx", &engineid, &enginelen,
246			&engine_boots, &engine_time, &user, &userlen, &offs2,
247			&digest, &digestlen, &salt, &saltlen) != 0) {
248			*errp = "cannot decode USM params";
249			goto done;
250			}
251
252			log_debug("USM: engineid '%s', engine boots %lld, engine time %lld, "
253			"user '%s'", tohexstr(engineid, enginelen), engine_boots,
254			engine_time, user);
255
256			if (enginelen > SNMPD_MAXENGINEIDLEN \|\|
257			userlen > SNMPD_MAXUSERNAMELEN \|\|
258			(digestlen != (MSG_HAS_AUTH(msg) ? SNMP_USM_DIGESTLEN : 0)) \|\|
259			(saltlen != (MSG_HAS_PRIV(msg) ? SNMP_USM_SALTLEN : 0))) {
260			*errp = "bad field length";
261			goto done;
262			}
263
264			if (enginelen != snmpd_env->sc_engineid_len \|\|
265			memcmp(engineid, snmpd_env->sc_engineid, enginelen) != 0) {
266			*errp = "unknown engine id";
267			msg->sm_usmerr = OIDVAL_usmErrEngineId;
268			stats->snmp_usmnosuchengine++;
269			goto done;
270			}
271
272			if (engine_boots != 0LL && engine_time != 0LL) {
273			now = snmpd_engine_time();
274			if (engine_boots != snmpd_env->sc_engine_boots \|\|
275			engine_time < (long long)(now - SNMP_MAX_TIMEWINDOW) \|\|
276			engine_time > (long long)(now + SNMP_MAX_TIMEWINDOW)) {
277			*errp = "out of time window";
278			msg->sm_usmerr = OIDVAL_usmErrTimeWindow;
279			stats->snmp_usmtimewindow++;
280			goto done;
281			}
282			}
283
284			msg->sm_engine_boots = (u_int32_t)engine_boots;
285			msg->sm_engine_time = (u_int32_t)engine_time;
286
287			memcpy(msg->sm_username, user, userlen);
288			msg->sm_username[userlen] = '\0';
289			msg->sm_user = usm_finduser(msg->sm_username);
290			if (msg->sm_user == NULL) {
291			*errp = "no such user";
292			msg->sm_usmerr = OIDVAL_usmErrUserName;
293			stats->snmp_usmnosuchuser++;
294			goto done;
295			}
296			if (MSG_SECLEVEL(msg) > msg->sm_user->uu_seclevel) {
297			*errp = "unsupported security model";
298			msg->sm_usmerr = OIDVAL_usmErrSecLevel;
299			stats->snmp_usmbadseclevel++;
300			goto done;
301			}
302
303			/*
304			* offs is the offset of the USM string within the serialized msg
305			* and offs2 the offset of the digest within the USM string.
306			*/
307			if (!usm_valid_digest(msg, offs + offs2, digest, digestlen)) {
308			*errp = "bad msg digest";
309			msg->sm_usmerr = OIDVAL_usmErrDigest;
310			stats->snmp_usmwrongdigest++;
311			goto done;
312			}
313
314			if (MSG_HAS_PRIV(msg)) {
315			memcpy(msg->sm_salt, salt, saltlen);
316			if ((decr = usm_decrypt(msg, elm->be_next)) == NULL) {
317			*errp = "cannot decrypt msg";
318			msg->sm_usmerr = OIDVAL_usmErrDecrypt;
319			stats->snmp_usmdecrypterr++;
320			goto done;
321			}
322			ber_replace_elements(elm, decr);
323			}
324			next = elm->be_next;
325
326			done:
327			ber_free(&ber);
328			if (usm != NULL)
329			ber_free_elements(usm);
330			return next;
331			}
332
333			struct ber_element *
334			usm_encode(struct snmp_message msg, struct ber_element e)
335			{
336			struct ber ber;
337			struct ber_element usm, a, *res = NULL;
338			void *ptr;
339			char digest[SNMP_USM_DIGESTLEN];
340			size_t digestlen, saltlen, len;
341
342			msg->sm_digest_offs = 0;
343			bzero(&ber, sizeof(ber));
344			ber.fd = -1;
345
346			usm = ber_add_sequence(NULL);
347
348			if (MSG_HAS_AUTH(msg)) {
349			/*
350			* Fill in enough zeroes and remember the position within the
351			* messages. The digest will be calculated once the message
352			* is complete.
353			*/
354			#ifdef DEBUG
355			assert(msg->sm_user != NULL);
356			#endif
357			bzero(digest, sizeof(digest));
358			digestlen = sizeof(digest);
359			} else
360			digestlen = 0;
361
362			if (MSG_HAS_PRIV(msg)) {
363			#ifdef DEBUG
364			assert(msg->sm_user != NULL);
365			#endif
366			++(msg->sm_user->uu_salt);
367			memcpy(msg->sm_salt, &msg->sm_user->uu_salt,
368			sizeof(msg->sm_salt));
369			saltlen = sizeof(msg->sm_salt);
370			} else
371			saltlen = 0;
372
373			msg->sm_engine_boots = (u_int32_t)snmpd_env->sc_engine_boots;
374			msg->sm_engine_time = (u_int32_t)snmpd_engine_time();
375			if ((a = ber_printf_elements(usm, "xdds",
376			snmpd_env->sc_engineid, snmpd_env->sc_engineid_len,
377			msg->sm_engine_boots, msg->sm_engine_time,
378			msg->sm_username)) == NULL)
379			goto done;
380
381			if ((a = ber_add_nstring(a, digest, digestlen)) == NULL)
382			goto done;
383			if (digestlen > 0)
384			ber_set_writecallback(a, usm_cb_digest, msg);
385
386			if ((a = ber_add_nstring(a, msg->sm_salt, saltlen)) == NULL)
387			goto done;
388
389			#ifdef DEBUG
390			fprintf(stderr, "encode USM parameters:\n");
391			smi_debug_elements(usm);
392			#endif
393			len = ber_write_elements(&ber, usm);
394			if (ber_get_writebuf(&ber, &ptr) > 0) {
395			res = ber_add_nstring(e, (char *)ptr, len);
396			if (digestlen > 0)
397			ber_set_writecallback(res, usm_cb_digest, msg);
398			}
399
400			done:
401			ber_free(&ber);
402			ber_free_elements(usm);
403			return res;
404			}
405
406			void
407			usm_cb_digest(void *arg, size_t offs)
408			{
409			struct snmp_message *msg = arg;
410			msg->sm_digest_offs += offs;
411			}
412
413			struct ber_element *
414			usm_encrypt(struct snmp_message msg, struct ber_element pdu)
415			{
416			struct ber ber;
417			struct ber_element *encrpdu = NULL;
418			void *ptr;
419			int len;
420			ssize_t elen;
421			u_char encbuf[READ_BUF_SIZE];
422
423			if (!MSG_HAS_PRIV(msg))
424			return pdu;
425
426			bzero(&ber, sizeof(ber));
427			ber.fd = -1;
428
429			#ifdef DEBUG
430			fprintf(stderr, "encrypted PDU:\n");
431			smi_debug_elements(pdu);
432			#endif
433
434			len = ber_write_elements(&ber, pdu);
435			if (ber_get_writebuf(&ber, &ptr) > 0) {
436			elen = usm_crypt(msg, ptr, len, encbuf, 1);
437			if (elen > 0)
438			encrpdu = ber_add_nstring(NULL, (char *)encbuf, elen);
439			}
440
441			ber_free(&ber);
442			ber_free_elements(pdu);
443			return encrpdu;
444			}
445
446			/*
447			* Calculate message digest and replace within message
448			*/
449			void
450			usm_finalize_digest(struct snmp_message msg, char buf, ssize_t len)
451			{
452			const EVP_MD *md;
453			u_char digest[EVP_MAX_MD_SIZE];
454			unsigned hlen;
455
456			if (msg->sm_resp == NULL \|\|
457			!MSG_HAS_AUTH(msg) \|\|
458			msg->sm_user == NULL \|\|
459			msg->sm_digest_offs == 0 \|\|
460			len <= 0)
461			return;
462			bzero(digest, SNMP_USM_DIGESTLEN);
463			#ifdef DEBUG
464			assert(msg->sm_digest_offs + SNMP_USM_DIGESTLEN <= (size_t)len);
465			assert(!memcmp(buf + msg->sm_digest_offs, digest, SNMP_USM_DIGESTLEN));
466			#endif
467
468			if ((md = usm_get_md(msg->sm_user->uu_auth)) == NULL)
469			return;
470
471			HMAC(md, msg->sm_user->uu_authkey, (int)msg->sm_user->uu_authkeylen,
472			(u_char*)buf, (size_t)len, digest, &hlen);
473
474			memcpy(buf + msg->sm_digest_offs, digest, SNMP_USM_DIGESTLEN);
475			return;
476			}
477
478			void
479			usm_make_report(struct snmp_message *msg)
480			{
481			struct ber_oid usmstat = OID(MIB_usmStats, 0, 0);
482
483			/* Always send report in clear-text */
484			msg->sm_flags = 0;
485			msg->sm_context = SNMP_C_REPORT;
486			msg->sm_username[0] = '\0';
487			usmstat.bo_id[OIDIDX_usmStats] = msg->sm_usmerr;
488			usmstat.bo_n = OIDIDX_usmStats + 2;
489			if (msg->sm_varbindresp != NULL)
490			ber_free_elements(msg->sm_varbindresp);
491			msg->sm_varbindresp = ber_add_sequence(NULL);
492			mps_getreq(NULL, msg->sm_varbindresp, &usmstat, msg->sm_version);
493			return;
494			}
495
496			int
497			usm_valid_digest(struct snmp_message *msg, off_t offs,
498			char *digest, size_t digestlen)
499			{
500			const EVP_MD *md;
501			u_char exp_digest[EVP_MAX_MD_SIZE];
502			unsigned hlen;
503
504			if (!MSG_HAS_AUTH(msg))
505			return 1;
506
507			if (digestlen != SNMP_USM_DIGESTLEN)
508			return 0;
509
510			#ifdef DEBUG
511			assert(offs + digestlen <= msg->sm_datalen);
512			assert(bcmp(&msg->sm_data[offs], digest, digestlen) == 0);
513			#endif
514
515			if ((md = usm_get_md(msg->sm_user->uu_auth)) == NULL)
516			return 0;
517
518			memset(&msg->sm_data[offs], 0, digestlen);
519			HMAC(md, msg->sm_user->uu_authkey, (int)msg->sm_user->uu_authkeylen,
520			msg->sm_data, msg->sm_datalen, exp_digest, &hlen);
521			/* we don't bother to restore the original message */
522
523			if (hlen < digestlen)
524			return 0;
525
526			return memcmp(digest, exp_digest, digestlen) == 0;
527			}
528
529			struct ber_element *
530			usm_decrypt(struct snmp_message msg, struct ber_element encr)
531			{
532			u_char *privstr;
533			size_t privlen;
534			u_char buf[READ_BUF_SIZE];
535			struct ber ber;
536			struct ber_element *scoped_pdu = NULL;
537			ssize_t scoped_pdu_len;
538
539			if (ber_get_nstring(encr, (void *)&privstr, &privlen) < 0)
540			return NULL;
541
542			scoped_pdu_len = usm_crypt(msg, privstr, (int)privlen, buf, 0);
543			if (scoped_pdu_len < 0)
544			return NULL;
545
546			bzero(&ber, sizeof(ber));
547			ber.fd = -1;
548			ber_set_readbuf(&ber, buf, scoped_pdu_len);
549			scoped_pdu = ber_read_elements(&ber, NULL);
550
551			#ifdef DEBUG
552			if (scoped_pdu != NULL) {
553			fprintf(stderr, "decrypted scoped PDU:\n");
554			smi_debug_elements(scoped_pdu);
555			}
556			#endif
557
558			ber_free(&ber);
559			return scoped_pdu;
560			}
561
562			ssize_t
563			usm_crypt(struct snmp_message msg, u_char inbuf, int inlen, u_char *outbuf,
564			int do_encrypt)
565			{
566			const EVP_CIPHER *cipher;
567			EVP_CIPHER_CTX ctx;
568			u_char *privkey;
569			int i;
570			u_char iv[EVP_MAX_IV_LENGTH];
571			int len, len2;
572			int rv;
573			u_int32_t ivv;
574
575			if ((cipher = usm_get_cipher(msg->sm_user->uu_priv)) == NULL)
576			return -1;
577
578			privkey = (u_char *)msg->sm_user->uu_privkey;
579			#ifdef DEBUG
580			assert(privkey != NULL);
581			#endif
582			switch (msg->sm_user->uu_priv) {
583			case PRIV_DES:
584			/* RFC3414, chap 8.1.1.1. */
585			for (i = 0; i < 8; i++)
586			iv[i] = msg->sm_salt[i] ^ privkey[SNMP_USM_SALTLEN + i];
587			break;
588			case PRIV_AES:
589			/* RFC3826, chap 3.1.2.1. */
590			ivv = htobe32(msg->sm_engine_boots);
591			memcpy(iv, &ivv, sizeof(ivv));
592			ivv = htobe32(msg->sm_engine_time);
593			memcpy(iv + sizeof(ivv), &ivv, sizeof(ivv));
594			memcpy(iv + 2 * sizeof(ivv), msg->sm_salt, SNMP_USM_SALTLEN);
595			break;
596			default:
597			return -1;
598			}
599
600			if (!EVP_CipherInit(&ctx, cipher, privkey, iv, do_encrypt))
601			return -1;
602
603			if (!do_encrypt)
604			EVP_CIPHER_CTX_set_padding(&ctx, 0);
605
606			if (EVP_CipherUpdate(&ctx, outbuf, &len, inbuf, inlen) &&
607			EVP_CipherFinal_ex(&ctx, outbuf + len, &len2))
608			rv = len + len2;
609			else
610			rv = -1;
611
612			EVP_CIPHER_CTX_cleanup(&ctx);
613			return rv;
614			}
615
616			/*
617			* RFC3414, Password to Key Algorithm
618			*/
619			char *
620			usm_passwd2key(const EVP_MD md, char passwd, int *maxlen)
621			{
622			EVP_MD_CTX ctx;
623			int i, count;
624			u_char pw, c;
625			u_char pwbuf[2 * EVP_MAX_MD_SIZE + SNMPD_MAXENGINEIDLEN];
626			u_char keybuf[EVP_MAX_MD_SIZE];
627			unsigned dlen;
628			char *key;
629
630			EVP_DigestInit(&ctx, md);
631			pw = (u_char *)passwd;
632			for (count = 0; count < 1048576; count += 64) {
633			c = pwbuf;
634			for (i = 0; i < 64; i++) {
635			if (*pw == '\0')
636			pw = (u_char *)passwd;
637			c++ = pw++;
638			}
639			EVP_DigestUpdate(&ctx, pwbuf, 64);
640			}
641			EVP_DigestFinal(&ctx, keybuf, &dlen);
642			EVP_MD_CTX_cleanup(&ctx);
643
644			/* Localize the key */
645			#ifdef DEBUG
646			assert(snmpd_env->sc_engineid_len <= SNMPD_MAXENGINEIDLEN);
647			#endif
648			memcpy(pwbuf, keybuf, dlen);
649			memcpy(pwbuf + dlen, snmpd_env->sc_engineid,
650			snmpd_env->sc_engineid_len);
651			memcpy(pwbuf + dlen + snmpd_env->sc_engineid_len, keybuf, dlen);
652
653			EVP_DigestInit(&ctx, md);
654			EVP_DigestUpdate(&ctx, pwbuf, 2 * dlen + snmpd_env->sc_engineid_len);
655			EVP_DigestFinal(&ctx, keybuf, &dlen);
656			EVP_MD_CTX_cleanup(&ctx);
657
658			if (maxlen > 0 && dlen > (unsigned)maxlen)
659			dlen = (unsigned)*maxlen;
660			if ((key = malloc(dlen)) == NULL)
661			fatal("key");
662			memcpy(key, keybuf, dlen);
663			*maxlen = (int)dlen;
664			return key;
665			}