Add support for SNMPv3/USM privacy.

net-snmp's -3K is supported via the -K parameter, -3K is not supported.

Feedback and OK jmatthew@

1 files changed, 210 insertions, 22 deletions

diff --git a/usr.bin/snmp/usm.c b/usr.bin/snmp/usm.c
index 1ca43316b43..7da977c9b25 100644
--- a/usr.bin/snmp/usm.c
+++ b/usr.bin/snmp/usm.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: usm.c,v 1.2 2019/09/18 09:52:47 martijn Exp $	*/
+/*	$OpenBSD: usm.c,v 1.3 2019/09/18 09:54:36 martijn Exp $	*/
 
 /*
  * Copyright (c) 2019 Martijn van Duren <martijn@openbsd.org>
@@ -44,6 +44,9 @@ struct usm_sec {
 	enum usm_key_level authlevel;
 	const EVP_MD *digest;
 	char *authkey;
+	enum usm_key_level privlevel;
+	const EVP_CIPHER *cipher;
+	char *privkey;
 	int bootsset;
 	uint32_t boots;
 	int timeset;
@@ -53,13 +56,21 @@ struct usm_sec {
 
 struct usm_cookie {
 	size_t digestoffset;
+	long long salt;
+	uint32_t boots;
+	uint32_t time;
 };
 
 static int usm_doinit(struct snmp_agent *);
 static char *usm_genparams(struct snmp_agent *, size_t *, void **);
 static int usm_finalparams(struct snmp_agent *, char *, size_t, size_t, void *);
+static struct ber_element *usm_encpdu(struct snmp_agent *agent,
+    struct ber_element *pdu, void *cookie);
+static char *usm_crypt(const EVP_CIPHER *, int, char *, struct usm_cookie *,
+    char *, size_t, size_t *);
 static int usm_parseparams(struct snmp_agent *, char *, size_t, off_t, char *,
-    size_t, uint8_t);
+    size_t, uint8_t, void **);
+struct ber_element *usm_decpdu(struct snmp_agent *, char *, size_t, void *);
 static void usm_digest_pos(void *, size_t);
 static void usm_free(void *);
 static char *usm_passwd2mkey(const EVP_MD *, const char *);
@@ -95,7 +106,9 @@ usm_init(const char *user, size_t userlen)
 	sec->model = SNMP_SEC_USM;
 	sec->init = usm_doinit;
 	sec->genparams = usm_genparams;
+	sec->encpdu = usm_encpdu;
 	sec->parseparams = usm_parseparams;
+	sec->decpdu = usm_decpdu;
 	sec->finalparams = usm_finalparams;
 	sec->free = usm_free;
 	sec->freecookie = free;
@@ -139,12 +152,11 @@ usm_genparams(struct snmp_agent *agent, size_t *len, void **cookie)
 	struct ber_element *params, *digestelm;
 	struct usm_sec *usm = agent->v3->sec->data;
 	char digest[USM_MAX_DIGESTLEN];
-	size_t digestlen = 0;
+	size_t digestlen = 0, saltlen = 0;
 	char *secparams = NULL;
 	ssize_t berlen = 0;
 	struct usm_cookie *usmcookie;
 	struct timespec now, timediff;
-	uint32_t boots, time;
 
 	bzero(digest, sizeof(digest));
 
@@ -152,21 +164,27 @@ usm_genparams(struct snmp_agent *agent, size_t *len, void **cookie)
 		return NULL;
 	*cookie = usmcookie;
 
+	arc4random_buf(&(usmcookie->salt), sizeof(usmcookie->salt));
 	if (usm->timeset) {
 		if (clock_gettime(CLOCK_MONOTONIC, &now) == -1) {
 			free(usmcookie);
 			return NULL;
 		}
 		timespecsub(&now, &(usm->timecheck), &timediff);
-		time = usm->time + timediff.tv_sec;
+		usmcookie->time = usm->time + timediff.tv_sec;
 	} else
-		time = 0;
-	boots = usm->boots;
+		usmcookie->time = 0;
+	usmcookie->boots = usm->boots;
+
 	if (agent->v3->level & SNMP_MSGFLAG_AUTH)
 		digestlen = usm_digestlen(usm->digest);
+	if (agent->v3->level & SNMP_MSGFLAG_PRIV)
+	    saltlen = sizeof(usmcookie->salt);
+
 	if ((params = ber_printf_elements(NULL, "{xddxxx}", usm->engineid,
-	    usm->engineidlen, boots, time, usm->user, usm->userlen, digest,
-	    digestlen, NULL, (size_t) 0)) == NULL) {
+	    usm->engineidlen, usmcookie->boots, usmcookie->time, usm->user,
+	    usm->userlen, digest, digestlen, &(usmcookie->salt),
+	    saltlen)) == NULL) {
 		free(usmcookie);
 		return NULL;
 	}
@@ -190,6 +208,93 @@ usm_genparams(struct snmp_agent *agent, size_t *len, void **cookie)
 	return secparams;
 }
 
+static struct ber_element *
+usm_encpdu(struct snmp_agent *agent, struct ber_element *pdu, void *cookie)
+{
+	struct usm_sec *usm = agent->v3->sec->data;
+	struct usm_cookie *usmcookie = cookie;
+	struct ber ber;
+	struct ber_element *retpdu;
+	char *serialpdu, *encpdu;
+	ssize_t pdulen;
+	size_t encpdulen;
+
+	bzero(&ber, sizeof(ber));
+	ber_set_application(&ber, smi_application);
+	pdulen = ber_write_elements(&ber, pdu);
+	if (pdulen == -1)
+		return NULL;
+
+	ber_get_writebuf(&ber, (void **)&serialpdu);
+
+	encpdu = usm_crypt(usm->cipher, 1, usm->privkey, usmcookie, serialpdu,
+	    pdulen, &encpdulen);
+	ber_free(&ber);
+	if (encpdu == NULL)
+		return NULL;
+
+	retpdu = ber_add_nstring(NULL, encpdu, encpdulen);
+	free(encpdu);
+	return retpdu;
+}
+
+static char *
+usm_crypt(const EVP_CIPHER *cipher, int do_enc, char *key,
+    struct usm_cookie *cookie, char *serialpdu, size_t pdulen, size_t *outlen)
+{
+	EVP_CIPHER_CTX ctx;
+	size_t i;
+	char iv[EVP_MAX_IV_LENGTH];
+	char *salt = (char *)&(cookie->salt);
+	char *outtext;
+	int len, len2, bs;
+	uint32_t ivv;
+
+	switch (EVP_CIPHER_type(cipher)) {
+	case NID_des_cbc:
+		/* RFC3414, chap 8.1.1.1. */
+		for (i = 0; i < 8; i++)
+			iv[i] = salt[i] ^ key[USM_SALTOFFSET + i];
+		break;
+	case NID_aes_128_cfb128:
+		/* RFC3826, chap 3.1.2.1. */
+		ivv = htobe32(cookie->boots);
+		memcpy(iv, &ivv, sizeof(ivv));
+		ivv = htobe32(cookie->time);
+		memcpy(iv + sizeof(ivv), &ivv, sizeof(ivv));
+		memcpy(iv + 2 * sizeof(ivv), &(cookie->salt),
+		    sizeof(cookie->salt));
+		break;
+	default:
+		return NULL;
+	}
+
+	bzero(&ctx, sizeof(ctx));
+	if (!EVP_CipherInit(&ctx, cipher, key, iv, do_enc))
+		return NULL;
+
+	EVP_CIPHER_CTX_set_padding(&ctx, do_enc);
+
+	bs = EVP_CIPHER_block_size(cipher);
+	/* Maximum output size */
+	*outlen = pdulen + (bs - (pdulen % bs));
+
+	if ((outtext = malloc(*outlen)) == NULL)
+		return NULL;
+
+	if (EVP_CipherUpdate(&ctx, outtext, &len, serialpdu, pdulen) &&
+	    EVP_CipherFinal_ex(&ctx, outtext + len, &len2))
+		*outlen = len + len2;
+	else {
+		free(outtext);
+		outtext = NULL;
+	}
+
+	EVP_CIPHER_CTX_cleanup(&ctx);
+
+	return outtext;
+}
+
 static int
 usm_finalparams(struct snmp_agent *agent, char *buf, size_t buflen,
     size_t secparamsoffset, void *cookie)
@@ -215,17 +320,18 @@ usm_finalparams(struct snmp_agent *agent, char *buf, size_t buflen,
 
 static int
 usm_parseparams(struct snmp_agent *agent, char *packet, size_t packetlen,
-    off_t secparamsoffset, char *buf, size_t buflen, uint8_t level)
+    off_t secparamsoffset, char *buf, size_t buflen, uint8_t level,
+    void **cookie)
 {
 	struct usm_sec *usm = agent->v3->sec->data;
 	struct ber ber;
 	struct ber_element *secparams;
-	char *engineid, *user, *digest;
-	size_t engineidlen, userlen, digestlen;
+	char *engineid, *user, *digest, *salt;
+	size_t engineidlen, userlen, digestlen, saltlen;
 	struct timespec now, timediff;
 	off_t digestoffset;
 	char exp_digest[EVP_MAX_MD_SIZE];
-	uint32_t boots, time;
+	struct usm_cookie *usmcookie;
 
 	bzero(&ber, sizeof(ber));
 	bzero(exp_digest, sizeof(exp_digest));
@@ -236,10 +342,17 @@ usm_parseparams(struct snmp_agent *agent, char *packet, size_t packetlen,
 		return -1;
 	ber_free(&ber);
 
-	if (ber_scanf_elements(secparams, "{xddxpxS}", &engineid, &engineidlen,
-	    &boots, &time, &user, &userlen, &digestoffset, &digest,
-	    &digestlen) == -1)
+	if ((usmcookie = malloc(sizeof(*usmcookie))) == NULL)
 		goto fail;
+	*cookie = usmcookie;
+
+	if (ber_scanf_elements(secparams, "{xddxpxx}", &engineid, &engineidlen,
+	    &(usmcookie->boots), &(usmcookie->time), &user, &userlen,
+	    &digestoffset, &digest, &digestlen, &salt, &saltlen) == -1)
+		goto fail;
+	if (saltlen != sizeof(usmcookie->salt) && saltlen != 0)
+		goto fail;
+	memcpy(&(usmcookie->salt), salt, saltlen);
 
 	if (!usm->engineidset) {
 		if (usm_setengineid(agent->v3->sec, engineid,
@@ -253,12 +366,12 @@ usm_parseparams(struct snmp_agent *agent, char *packet, size_t packetlen,
 	}
 
 	if (!usm->bootsset) {
-		usm->boots = boots;
+		usm->boots = usmcookie->boots;
 		usm->bootsset = 1;
 	} else {
-		if (boots < usm->boots)
+		if (usmcookie->boots < usm->boots)
 			goto fail;
-		if (boots > usm->boots) {
+		if (usmcookie->boots > usm->boots) {
 			usm->bootsset = 0;
 			usm->timeset = 0;
 			usm_doinit(agent);
@@ -267,7 +380,7 @@ usm_parseparams(struct snmp_agent *agent, char *packet, size_t packetlen,
 	}
 
 	if (!usm->timeset) {
-		usm->time = time;
+		usm->time = usmcookie->time;
 		if (clock_gettime(CLOCK_MONOTONIC, &usm->timecheck) == -1)
 			goto fail;
 		usm->timeset = 1;
@@ -275,8 +388,10 @@ usm_parseparams(struct snmp_agent *agent, char *packet, size_t packetlen,
 		if (clock_gettime(CLOCK_MONOTONIC, &now) == -1)
 			goto fail;
 		timespecsub(&now, &(usm->timecheck), &timediff);
-		if (time < usm->time + timediff.tv_sec - USM_MAX_TIMEWINDOW ||
-		    time > usm->time + timediff.tv_sec + USM_MAX_TIMEWINDOW) {
+		if (usmcookie->time <
+		    usm->time + timediff.tv_sec - USM_MAX_TIMEWINDOW ||
+		    usmcookie->time >
+		    usm->time + timediff.tv_sec + USM_MAX_TIMEWINDOW) {
 			usm->bootsset = 0;
 			usm->timeset = 0;
 			usm_doinit(agent);
@@ -308,10 +423,35 @@ usm_parseparams(struct snmp_agent *agent, char *packet, size_t packetlen,
 	return 0;
 
 fail:
+	free(usmcookie);
 	ber_free_element(secparams);
 	return -1;
 }
 
+struct ber_element *
+usm_decpdu(struct snmp_agent *agent, char *encpdu, size_t encpdulen, void *cookie)
+{
+	struct usm_sec *usm = agent->v3->sec->data;
+	struct usm_cookie *usmcookie = cookie;
+	struct ber ber;
+	struct ber_element *scopedpdu;
+	char *rawpdu;
+	size_t rawpdulen;
+
+	if ((rawpdu = usm_crypt(usm->cipher, 0, usm->privkey, usmcookie,
+	    encpdu, encpdulen, &rawpdulen)) == NULL)
+		return NULL;
+
+	bzero(&ber, sizeof(ber));
+	ber_set_application(&ber, smi_application);
+	ber_set_readbuf(&ber, rawpdu, rawpdulen);
+	scopedpdu = ber_read_elements(&ber, NULL);
+	ber_free(&ber);
+	free(rawpdu);
+
+	return scopedpdu;
+}
+
 static void
 usm_digest_pos(void *data, size_t offset)
 {
@@ -327,6 +467,7 @@ usm_free(void *data)
 
 	free(usm->user);
 	free(usm->authkey);
+	free(usm->privkey);
 	free(usm->engineid);
 	free(usm);
 }
@@ -365,6 +506,43 @@ usm_setauth(struct snmp_sec *sec, const EVP_MD *digest, const char *key,
 }
 
 int
+usm_setpriv(struct snmp_sec *sec, const EVP_CIPHER *cipher, const char *key,
+    size_t keylen, enum usm_key_level level)
+{
+	struct usm_sec *usm = sec->data;
+	char *lkey;
+
+	if (usm->digest == NULL) {
+		errno = EINVAL;
+		return -1;
+	}
+
+	/*
+	 * We could transform a master key to a local key here if we already
+	 * have usm_setengineid called. Sine snmpc.c is the only caller at
+	 * the moment there's no need, since it always calls us first.
+	 */
+	if (level == USM_KEY_PASSWORD) {
+		if ((usm->privkey = usm_passwd2mkey(usm->digest, key)) == NULL)
+			return -1;
+		level = USM_KEY_MASTER;
+		keylen = EVP_MD_size(usm->digest);
+	} else {
+		if (keylen != (size_t)EVP_MD_size(usm->digest)) {
+			errno = EINVAL;
+			return -1;
+		}
+		if ((lkey = malloc(keylen)) == NULL)
+			return -1;
+		memcpy(lkey, key, keylen);
+		usm->privkey = lkey;
+	}
+	usm->cipher = cipher;
+	usm->privlevel = level;
+	return 0;
+}
+
+int
 usm_setengineid(struct snmp_sec *sec, char *engineid, size_t engineidlen)
 {
 	struct usm_sec *usm = sec->data;
@@ -388,6 +566,16 @@ usm_setengineid(struct snmp_sec *sec, char *engineid, size_t engineidlen)
 		free(mkey);
 		usm->authlevel = USM_KEY_LOCALIZED;
 	}
+	if (usm->privlevel == USM_KEY_MASTER) {
+		mkey = usm->privkey;
+		if ((usm->privkey = usm_mkey2lkey(usm, usm->digest,
+		    mkey)) == NULL) {
+			usm->privkey = mkey;
+			return -1;
+		}
+		free(mkey);
+		usm->privlevel = USM_KEY_LOCALIZED;
+	}
 
 	return 0;
 }