/* dnscache.c
 * Implementation of a real DNS cache
 *
 * File begun on 2011-06-06 by RGerhards
 * The initial implementation is far from being optimal. The idea is to
 * first get somethting that'S functionally OK, and then evolve the algorithm.
 * In any case, even the initial implementaton is far faster than what we had
 * before. -- rgerhards, 2011-06-06
 *
 * Copyright 2011-2019 by Rainer Gerhards and Adiscon GmbH.
 *
 * This file is part of the rsyslog runtime library.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *       -or-
 *       see COPYING.ASL20 in the source distribution
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
#include "config.h"

#include "rsyslog.h"
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <netdb.h>
#include <unistd.h>
#include <ctype.h>

#include "syslogd-types.h"
#include "glbl.h"
#include "errmsg.h"
#include "obj.h"
#include "unicode-helper.h"
#include "net.h"
#include "hashtable.h"
#include "prop.h"
#include "dnscache.h"

/* module data structures */
struct dnscache_entry_s {
	struct sockaddr_storage addr;
	prop_t *fqdn;
	prop_t *fqdnLowerCase;
	prop_t *localName; /* only local name, without domain part (if configured so) */
	prop_t *ip;
	time_t validUntil;
	struct dnscache_entry_s *next;
	unsigned nUsed;
};
typedef struct dnscache_entry_s dnscache_entry_t;
struct dnscache_s {
	pthread_rwlock_t rwlock;
	struct hashtable *ht;
	unsigned nEntries;
};
typedef struct dnscache_s dnscache_t;

unsigned dnscacheDefaultTTL = 24 * 60 * 60; /* 24 hrs default TTL */
int dnscacheEnableTTL = 0; /* expire entries or not (0) ? */


/* static data */
DEFobjStaticHelpers
DEFobjCurrIf(glbl)
DEFobjCurrIf(prop)
static dnscache_t dnsCache;
static prop_t *staticErrValue;


/* Our hash function.
 */
static unsigned int
hash_from_key_fn(void *k)
{
	int len = 0;
	uchar *rkey; /* we treat this as opaque bytes */
	unsigned hashval = 1;

	switch (((struct sockaddr *)k)->sa_family) {
		case AF_INET:
			len = sizeof (struct in_addr);
			rkey = (uchar*) &(((struct sockaddr_in *)k)->sin_addr);
			break;
		case AF_INET6:
			len = sizeof (struct in6_addr);
			rkey = (uchar*) &(((struct sockaddr_in6 *)k)->sin6_addr);
			break;
		default:
			dbgprintf("hash_from_key_fn: unknown address family!\n");
			len = 0;
			rkey = NULL;
	}
	while(len--)
		hashval = hashval * 33 + *rkey++;

	return hashval;
}


static int
key_equals_fn(void *key1, void *key2)
{
	int RetVal = 0;

	if(((struct sockaddr *)key1)->sa_family != ((struct sockaddr *)key2)->sa_family) {
		return 0;
	}
	switch (((struct sockaddr *)key1)->sa_family) {
		case AF_INET:
			RetVal = !memcmp(&((struct sockaddr_in *)key1)->sin_addr,
				&((struct sockaddr_in *)key2)->sin_addr, sizeof (struct in_addr));
			break;
		case AF_INET6:
			RetVal = !memcmp(&((struct sockaddr_in6 *)key1)->sin6_addr,
				&((struct sockaddr_in6 *)key2)->sin6_addr, sizeof (struct in6_addr));
			break;
	}

	return RetVal;
}

/* destruct a cache entry.
 * Precondition: entry must already be unlinked from list
 */
static void ATTR_NONNULL()
entryDestruct(dnscache_entry_t *const etry)
{
	if(etry->fqdn != NULL)
		prop.Destruct(&etry->fqdn);
	if(etry->fqdnLowerCase != NULL)
		prop.Destruct(&etry->fqdnLowerCase);
	if(etry->localName != NULL)
		prop.Destruct(&etry->localName);
	if(etry->ip != NULL)
		prop.Destruct(&etry->ip);
	free(etry);
}

/* init function (must be called once) */
rsRetVal
dnscacheInit(void)
{
	DEFiRet;
	if((dnsCache.ht = create_hashtable(100, hash_from_key_fn, key_equals_fn,
				(void(*)(void*))entryDestruct)) == NULL) {
		DBGPRINTF("dnscache: error creating hash table!\n");
		ABORT_FINALIZE(RS_RET_ERR); // TODO: make this degrade, but run!
	}
	dnsCache.nEntries = 0;
	pthread_rwlock_init(&dnsCache.rwlock, NULL);
	CHKiRet(objGetObjInterface(&obj)); /* this provides the root pointer for all other queries */
	CHKiRet(objUse(glbl, CORE_COMPONENT));
	CHKiRet(objUse(prop, CORE_COMPONENT));

	prop.Construct(&staticErrValue);
	prop.SetString(staticErrValue, (uchar*)"???", 3);
	prop.ConstructFinalize(staticErrValue);
finalize_it:
	RETiRet;
}

/* deinit function (must be called once) */
rsRetVal
dnscacheDeinit(void)
{
	DEFiRet;
	prop.Destruct(&staticErrValue);
	hashtable_destroy(dnsCache.ht, 1); /* 1 => free all values automatically */
	pthread_rwlock_destroy(&dnsCache.rwlock);
	objRelease(glbl, CORE_COMPONENT);
	objRelease(prop, CORE_COMPONENT);
	RETiRet;
}


/* This is a cancel-safe getnameinfo() version, because we learned
 * (via drd/valgrind) that getnameinfo() seems to have some issues
 * when being cancelled, at least if the module was dlloaded.
 * rgerhards, 2008-09-30
 */
static int
mygetnameinfo(const struct sockaddr *sa, socklen_t salen,
		char *host, size_t hostlen,
		char *serv, size_t servlen, int flags)
{
	int iCancelStateSave;
	int i;

	pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &iCancelStateSave);
	i = getnameinfo(sa, salen, host, hostlen, serv, servlen, flags);
	pthread_setcancelstate(iCancelStateSave, NULL);
	return i;
}


/* get only the local part of the hostname and set it in cache entry */
static void
setLocalHostName(dnscache_entry_t *etry)
{
	uchar *fqdnLower;
	uchar *p;
	int i;
	uchar hostbuf[NI_MAXHOST];

	if(glbl.GetPreserveFQDN()) {
		prop.AddRef(etry->fqdnLowerCase);
		etry->localName = etry->fqdnLowerCase;
		goto done;
	}

	/* strip domain, if configured for this entry */
	fqdnLower = propGetSzStr(etry->fqdnLowerCase);
	p = (uchar*)strchr((char*)fqdnLower, '.'); /* find start of domain name "machine.example.com" */
	if(p == NULL) { /* do we have a domain part? */
		prop.AddRef(etry->fqdnLowerCase); /* no! */
		etry->localName = etry->fqdnLowerCase;
		goto done;
	}

	i = p - fqdnLower; /* length of hostname */
	memcpy(hostbuf, fqdnLower, i);
	hostbuf[i] = '\0';

	/* at this point, we have not found anything, so we again use the
	 * already-created complete full name property.
	 */
	prop.AddRef(etry->fqdnLowerCase);
	etry->localName = etry->fqdnLowerCase;
done:	return;
}


/* resolve an address.
 *
 * Please see http://www.hmug.org/man/3/getnameinfo.php (under Caveats)
 * for some explanation of the code found below. We do by default not
 * discard message where we detected malicouos DNS PTR records. However,
 * there is a user-configurabel option that will tell us if
 * we should abort. For this, the return value tells the caller if the
 * message should be processed (1) or discarded (0).
 */
static rsRetVal ATTR_NONNULL()
resolveAddr(struct sockaddr_storage *addr, dnscache_entry_t *etry)
{
	DEFiRet;
	int error;
	sigset_t omask, nmask;
	struct addrinfo hints, *res;
	char szIP[80]; /* large enough for IPv6 */
	char fqdnBuf[NI_MAXHOST];
	rs_size_t fqdnLen;
	rs_size_t i;
	
	error = mygetnameinfo((struct sockaddr *)addr, SALEN((struct sockaddr *)addr),
			    (char*) szIP, sizeof(szIP), NULL, 0, NI_NUMERICHOST);
	if(error) {
		dbgprintf("Malformed from address %s\n", gai_strerror(error));
		ABORT_FINALIZE(RS_RET_INVALID_SOURCE);
	}

	if(!glbl.GetDisableDNS()) {
		sigemptyset(&nmask);
		sigaddset(&nmask, SIGHUP);
		pthread_sigmask(SIG_BLOCK, &nmask, &omask);

		error = mygetnameinfo((struct sockaddr *)addr, SALEN((struct sockaddr *) addr),
				    fqdnBuf, NI_MAXHOST, NULL, 0, NI_NAMEREQD);

		if(error == 0) {
			memset (&hints, 0, sizeof (struct addrinfo));
			hints.ai_flags = AI_NUMERICHOST;

			/* we now do a lookup once again. This one should fail,
			 * because we should not have obtained a non-numeric address. If
			 * we got a numeric one, someone messed with DNS!
			 */
			if(getaddrinfo (fqdnBuf, NULL, &hints, &res) == 0) {
				freeaddrinfo (res);
				/* OK, we know we have evil. The question now is what to do about
				 * it. One the one hand, the message might probably be intended
				 * to harm us. On the other hand, losing the message may also harm us.
				 * Thus, the behaviour is controlled by the $DropMsgsWithMaliciousDnsPTRRecords
				 * option. If it tells us we should discard, we do so, else we proceed,
				 * but log an error message together with it.
				 * time being, we simply drop the name we obtained and use the IP - that one
				 * is OK in any way. We do also log the error message. rgerhards, 2007-07-16
		 		 */
		 		if(glbl.GetDropMalPTRMsgs() == 1) {
					LogError(0, RS_RET_MALICIOUS_ENTITY,
						 "Malicious PTR record, message dropped "
						 "IP = \"%s\" HOST = \"%s\"",
						 szIP, fqdnBuf);
					pthread_sigmask(SIG_SETMASK, &omask, NULL);
					ABORT_FINALIZE(RS_RET_MALICIOUS_ENTITY);
				}

				/* Please note: we deal with a malicous entry. Thus, we have crafted
				 * the snprintf() below so that all text is in front of the entry - maybe
				 * it contains characters that make the message unreadable
				 * (OK, I admit this is more or less impossible, but I am paranoid...)
				 * rgerhards, 2007-07-16
				 */
				LogError(0, NO_ERRCODE,
					 "Malicious PTR record (message accepted, but used IP "
					 "instead of PTR name: IP = \"%s\" HOST = \"%s\"",
					 szIP, fqdnBuf);

				error = 1; /* that will trigger using IP address below. */
			} else {/* we have a valid entry, so let's create the respective properties */
				fqdnLen = strlen(fqdnBuf);
				prop.CreateStringProp(&etry->fqdn, (uchar*)fqdnBuf, fqdnLen);
				for(i = 0 ; i < fqdnLen ; ++i)
					fqdnBuf[i] = tolower(fqdnBuf[i]);
				prop.CreateStringProp(&etry->fqdnLowerCase, (uchar*)fqdnBuf, fqdnLen);
			}
		}
		pthread_sigmask(SIG_SETMASK, &omask, NULL);
	}


finalize_it:
	if(iRet != RS_RET_OK) {
		strcpy(szIP, "?error.obtaining.ip?");
		error = 1; /* trigger hostname copies below! */
	}

	prop.CreateStringProp(&etry->ip, (uchar*)szIP, strlen(szIP));

	if(error || glbl.GetDisableDNS()) {
		dbgprintf("Host name for your address (%s) unknown\n", szIP);
		prop.AddRef(etry->ip);
		etry->fqdn = etry->ip;
		prop.AddRef(etry->ip);
		etry->fqdnLowerCase = etry->ip;
	}

	setLocalHostName(etry);

	RETiRet;
}


static rsRetVal ATTR_NONNULL()
addEntry(struct sockaddr_storage *const addr, dnscache_entry_t **const pEtry)
{
	int r;
	dnscache_entry_t *etry = NULL;
	DEFiRet;

	/* entry still does not exist, so add it */
	struct sockaddr_storage *const keybuf =  malloc(sizeof(struct sockaddr_storage));
	CHKmalloc(keybuf);
	CHKmalloc(etry = malloc(sizeof(dnscache_entry_t)));
	resolveAddr(addr, etry);
	assert(etry != NULL);
	memcpy(&etry->addr, addr, SALEN((struct sockaddr*) addr));
	etry->nUsed = 0;
	if(dnscacheEnableTTL) {
		etry->validUntil = time(NULL) + dnscacheDefaultTTL;
	}

	memcpy(keybuf, addr, sizeof(struct sockaddr_storage));

	r = hashtable_insert(dnsCache.ht, keybuf, etry);
	if(r == 0) {
		DBGPRINTF("dnscache: inserting element failed\n");
	}
	*pEtry = etry;

finalize_it:
	if(iRet != RS_RET_OK) {
		free(keybuf);
	}
	RETiRet;
}


static rsRetVal ATTR_NONNULL(1, 5)
findEntry(struct sockaddr_storage *const addr,
	prop_t **const fqdn, prop_t **const fqdnLowerCase,
	prop_t **const localName, prop_t **const ip)
{
	DEFiRet;

	pthread_rwlock_rdlock(&dnsCache.rwlock);
	dnscache_entry_t * etry = hashtable_search(dnsCache.ht, addr);
	DBGPRINTF("findEntry: 1st lookup found %p\n", etry);

	if(etry == NULL || (dnscacheEnableTTL && (etry->validUntil <= time(NULL)))) {
		pthread_rwlock_unlock(&dnsCache.rwlock);
		pthread_rwlock_wrlock(&dnsCache.rwlock);
		etry = hashtable_search(dnsCache.ht, addr); /* re-query, might have changed */
		DBGPRINTF("findEntry: 2nd lookup found %p\n", etry);
		if(etry == NULL || (dnscacheEnableTTL && (etry->validUntil <= time(NULL)))) {
			if(etry != NULL) {
				DBGPRINTF("hashtable: entry timed out, discarding it; "
					"valid until %lld, now %lld\n",
					(long long) etry->validUntil, (long long) time(NULL));
				dnscache_entry_t *const deleted = hashtable_remove(dnsCache.ht, addr);
				if(deleted != etry) {
					LogError(0, RS_RET_INTERNAL_ERROR, "dnscache %d: removed different "
						"hashtable entry than expected - please report issue; "
						"rsyslog version is %s", __LINE__, VERSION);
				}
				entryDestruct(etry);
			}
			/* now entry doesn't exist in any case, so let's (re)create it */
			CHKiRet(addEntry(addr, &etry));
		}
	}

	prop.AddRef(etry->ip);
	*ip = etry->ip;
	if(fqdn != NULL) {
		prop.AddRef(etry->fqdn);
		*fqdn = etry->fqdn;
	}
	if(fqdnLowerCase != NULL) {
		prop.AddRef(etry->fqdnLowerCase);
		*fqdnLowerCase = etry->fqdnLowerCase;
	}
	if(localName != NULL) {
		prop.AddRef(etry->localName);
		*localName = etry->localName;
	}

finalize_it:
	pthread_rwlock_unlock(&dnsCache.rwlock);
	RETiRet;
}


/* This is the main function: it looks up an entry and returns it's name
 * and IP address. If the entry is not yet inside the cache, it is added.
 * If the entry can not be resolved, an error is reported back. If fqdn
 * or fqdnLowerCase are NULL, they are not set.
 */
rsRetVal ATTR_NONNULL(1, 5)
dnscacheLookup(struct sockaddr_storage *const addr,
	prop_t **const fqdn, prop_t **const fqdnLowerCase,
	prop_t **const localName, prop_t **const ip)
{
	DEFiRet;

	iRet = findEntry(addr, fqdn, fqdnLowerCase, localName, ip);

	if(iRet != RS_RET_OK) {
		DBGPRINTF("dnscacheLookup failed with iRet %d\n", iRet);
		prop.AddRef(staticErrValue);
		*ip = staticErrValue;
		if(fqdn != NULL) {
			prop.AddRef(staticErrValue);
			*fqdn = staticErrValue;
		}
		if(fqdnLowerCase != NULL) {
			prop.AddRef(staticErrValue);
			*fqdnLowerCase = staticErrValue;
		}
		if(localName != NULL) {
			prop.AddRef(staticErrValue);
			*localName = staticErrValue;
		}
	}
	RETiRet;
}
