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Import snmp(1), a new snmp client which aims to be netsnmp compatible for
supported features.  It only supports get, getnext, walk, bulkget, bulkwalk,
trap, mibtree, and is SNMPv1 and SNMPv2c for now.

This will shortly replace snmpctl entirely. People using snmpctl are encouraged
to test and migrate to this code as soon as possible.

Much help with the manpage from schwarze@ and jmc@
No objections from reyk@
"Roll it in" deraadt@

/*	$OpenBSD: snmp.c,v 1.1 2019/08/09 06:17:59 martijn Exp $	*/

/*
 * Copyright (c) 2019 Martijn van Duren <martijn@openbsd.org>
 * Copyright (c) 2013 Reyk Floeter <reyk@openbsd.org>
 *
 * 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/socket.h>

#include <errno.h>
#include <poll.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <time.h>

#include "ber.h"
#include "smi.h"
#include "snmp.h"

static struct ber_element *
    snmp_resolve(struct snmp_agent *, struct ber_element *, int);

struct snmp_agent *
snmp_connect_v12(int fd, enum snmp_version version, const char *community)
{
	struct snmp_agent *agent;

	if (version != SNMP_V1 && version != SNMP_V2C) {
		errno = EINVAL;
		return NULL;
	}
	if ((agent = malloc(sizeof(*agent))) == NULL)
		return NULL;
	agent->fd = fd;
	agent->version = version;
	if ((agent->community = strdup(community)) == NULL)
		goto fail;
	agent->timeout = 1;
	agent->retries = 5;
	return agent;

fail:
	free(agent->community);
	free(agent);
	return NULL;
}

void
snmp_free_agent(struct snmp_agent *agent)
{
	free(agent->community);
	free(agent);
}

struct ber_element *
snmp_get(struct snmp_agent *agent, struct ber_oid *oid, size_t len)
{
	struct ber_element *pdu, *varbind;
	size_t i;

	if ((pdu = ber_add_sequence(NULL)) == NULL)
		return NULL;
	if ((varbind = ber_printf_elements(pdu, "tddd{", BER_CLASS_CONTEXT,
	    SNMP_C_GETREQ, arc4random() & 0x7fffffff, 0, 0)) == NULL)
		goto fail;
	for (i = 0; i < len; i++)
		varbind = ber_printf_elements(varbind, "{O0}", &oid[i]);
		if (varbind == NULL)
			goto fail;

	return snmp_resolve(agent, pdu, 1);
fail:
	ber_free_elements(pdu);
	return NULL;
}

struct ber_element *
snmp_getnext(struct snmp_agent *agent, struct ber_oid *oid, size_t len)
{
	struct ber_element *pdu, *varbind;
	size_t i;

	if ((pdu = ber_add_sequence(NULL)) == NULL)
		return NULL;
	if ((varbind = ber_printf_elements(pdu, "tddd{", BER_CLASS_CONTEXT,
	    SNMP_C_GETNEXTREQ, arc4random() & 0x7fffffff, 0, 0)) == NULL)
		goto fail;
	for (i = 0; i < len; i++)
		varbind = ber_printf_elements(varbind, "{O0}", &oid[i]);
		if (varbind == NULL)
			goto fail;

	return snmp_resolve(agent, pdu, 1);
fail:
	ber_free_elements(pdu);
	return NULL;
}

int
snmp_trap(struct snmp_agent *agent, struct timespec *uptime,
    struct ber_oid *oid, struct ber_element *custvarbind)
{
	struct ber_element *pdu, *varbind;
	struct ber_oid sysuptime, trap;
	long long ticks;

	if ((pdu = ber_add_sequence(NULL)) == NULL)
		return -1;
	if ((varbind = ber_printf_elements(pdu, "tddd{", BER_CLASS_CONTEXT,
	    SNMP_C_TRAPV2, arc4random() & 0x7fffffff, 0, 0)) == NULL)
		goto fail;

	ticks = uptime->tv_sec * 100;
	ticks += uptime->tv_nsec / 10000000;
	if (smi_string2oid("sysUpTime.0", &sysuptime) == -1)
		goto fail;
	if ((varbind = ber_printf_elements(varbind, "{Oit}", &sysuptime, ticks,
	    BER_CLASS_APPLICATION, SNMP_T_TIMETICKS)) == NULL)
		goto fail;
	if (smi_string2oid("snmpTrapOID.0", &trap) == -1)
		goto fail;
	if ((varbind = ber_printf_elements(varbind, "{OO}", &trap, oid)) == NULL)
		goto fail;
	if (custvarbind != NULL)
		ber_link_elements(varbind, custvarbind);

	snmp_resolve(agent, pdu, 0);
	return 0;
fail:
	ber_free_elements(pdu);
	return -1;
}

struct ber_element *
snmp_getbulk(struct snmp_agent *agent, struct ber_oid *oid, size_t len,
    int non_repeaters, int max_repetitions)
{
	struct ber_element *pdu, *varbind;
	size_t i;

	if ((pdu = ber_add_sequence(NULL)) == NULL)
		return NULL;
	if ((varbind = ber_printf_elements(pdu, "tddd{", BER_CLASS_CONTEXT,
	    SNMP_C_GETBULKREQ, arc4random() & 0x7fffffff, non_repeaters,
	    max_repetitions)) == NULL)
		goto fail;
	for (i = 0; i < len; i++)
		varbind = ber_printf_elements(varbind, "{O0}", &oid[i]);
		if (varbind == NULL)
			goto fail;

	return snmp_resolve(agent, pdu, 1);
fail:
	ber_free_elements(pdu);
	return NULL;
}

static struct ber_element *
snmp_resolve(struct snmp_agent *agent, struct ber_element *pdu, int reply)
{
	struct ber_element *message, *varbind;
	struct ber_oid oid;
	struct timespec start, now;
	struct pollfd pfd;
	struct ber ber;
	ssize_t len;
	long long reqid, rreqid;
	long long version;
	char *community;
	short direction;
	int to, nfds, ret;
	int tries;
	void *ptr;
	char buf[READ_BUF_SIZE];

	if (ber_scanf_elements(pdu, "{i", &reqid) != 0) {
		errno = EINVAL;
		ber_free_elements(pdu);
		return NULL;
	}

	if ((message = ber_add_sequence(NULL)) == NULL) {
		ber_free_elements(pdu);
		return NULL;
	}
	if (ber_printf_elements(message, "dse", agent->version,
	    agent->community, pdu) == NULL) {
		ber_free_elements(pdu);
		ber_free_elements(message);
		return NULL;
	}
	memset(&ber, 0, sizeof(ber));
	ber_set_application(&ber, smi_application);
	len = ber_write_elements(&ber, message);
	ber_free_elements(message);
	message = NULL;
	if (ber_get_writebuf(&ber, &ptr) < 1)
		goto fail;

	clock_gettime(CLOCK_MONOTONIC, &start);
	memcpy(&now, &start, sizeof(now));
	direction = POLLOUT;
	tries = agent->retries + 1;
	while (tries) {
		pfd.fd = agent->fd;
		pfd.events = direction;
		if (agent->timeout > 0) {
			to = (agent->timeout - (now.tv_sec - start.tv_sec)) * 1000;
			to -= (now.tv_nsec - start.tv_nsec) / 1000000;
		} else
			to = INFTIM;
		nfds = poll(&pfd, 1, to);
		if (nfds == 0) {
			errno = ETIMEDOUT;
			direction = POLLOUT;
			tries--;
			continue;
		}
		if (nfds == -1) {
			if (errno == EINTR)
				continue;
			else
				goto fail;
		}
		if (direction == POLLOUT) {
			ret = send(agent->fd, ptr, len, MSG_DONTWAIT);
			if (ret == -1)
				goto fail;
			if (ret < len) {
				errno = EBADMSG;
				goto fail;
			}
			if (!reply)
				return NULL;
			direction = POLLIN;
			continue;
		}
		ret = recv(agent->fd, buf, sizeof(buf), MSG_DONTWAIT);
		if (ret == 0)
			errno = ECONNRESET;
		if (ret <= 0)
			goto fail;
		ber_set_readbuf(&ber, buf, ret);
		if ((message = ber_read_elements(&ber, NULL)) == NULL)
			goto fail;
		if (ber_scanf_elements(message, "{ise", &version, &community,
		    &pdu) != 0)
			goto fail;
		/* Skip invalid packets; should not happen */
		if (version != agent->version ||
		    strcmp(community, agent->community) != 0)
			continue;
		/* Validate pdu format and check request id */
		if (ber_scanf_elements(pdu, "{iSSe", &rreqid, &varbind) != 0 ||
		    varbind->be_encoding != BER_TYPE_SEQUENCE)
			goto fail;
		if (rreqid != reqid)
			continue;
		for (varbind = varbind->be_sub; varbind != NULL;
		    varbind = varbind->be_next) {
			if (ber_scanf_elements(varbind, "{oS}", &oid) != 0)
				goto fail;
		}

		ber_unlink_elements(message->be_sub->be_next);
		ber_free_elements(message);
		ber_free(&ber);
		return pdu;
	}

fail:
	ber_free_elements(message);
	ber_free(&ber);
	return NULL;
}