Adding upstream version 3.5.24.upstream/3.5.24upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1216 insertions, 0 deletions

diff --git a/src/dns/dns_lookup.c b/src/dns/dns_lookup.c
new file mode 100644
index 0000000..c5f7ad9
--- /dev/null
+++ b/src/dns/dns_lookup.c
@@ -0,0 +1,1216 @@
+/*++
+/* NAME
+/*	dns_lookup 3
+/* SUMMARY
+/*	domain name service lookup
+/* SYNOPSIS
+/*	#include <dns.h>
+/*
+/*	int	dns_lookup(name, type, rflags, list, fqdn, why)
+/*	const char *name;
+/*	unsigned type;
+/*	unsigned rflags;
+/*	DNS_RR	**list;
+/*	VSTRING *fqdn;
+/*	VSTRING *why;
+/*
+/*	int	dns_lookup_l(name, rflags, list, fqdn, why, lflags, ltype, ...)
+/*	const char *name;
+/*	unsigned rflags;
+/*	DNS_RR	**list;
+/*	VSTRING *fqdn;
+/*	VSTRING *why;
+/*	int	lflags;
+/*	unsigned ltype;
+/*
+/*	int	dns_lookup_v(name, rflags, list, fqdn, why, lflags, ltype)
+/*	const char *name;
+/*	unsigned rflags;
+/*	DNS_RR	**list;
+/*	VSTRING *fqdn;
+/*	VSTRING *why;
+/*	int	lflags;
+/*	unsigned *ltype;
+/* AUXILIARY FUNCTIONS
+/*	extern int var_dns_ncache_ttl_fix;
+/*
+/*	int	dns_lookup_r(name, type, rflags, list, fqdn, why, rcode)
+/*	const char *name;
+/*	unsigned type;
+/*	unsigned rflags;
+/*	DNS_RR	**list;
+/*	VSTRING *fqdn;
+/*	VSTRING *why;
+/*	int	*rcode;
+/*
+/*	int	dns_lookup_rl(name, rflags, list, fqdn, why, rcode, lflags,
+/*				ltype, ...)
+/*	const char *name;
+/*	unsigned rflags;
+/*	DNS_RR	**list;
+/*	VSTRING *fqdn;
+/*	VSTRING *why;
+/*	int	*rcode;
+/*	int	lflags;
+/*	unsigned ltype;
+/*
+/*	int	dns_lookup_rv(name, rflags, list, fqdn, why, rcode, lflags,
+/*				ltype)
+/*	const char *name;
+/*	unsigned rflags;
+/*	DNS_RR	**list;
+/*	VSTRING *fqdn;
+/*	VSTRING *why;
+/*	int	*rcode;
+/*	int	lflags;
+/*	unsigned *ltype;
+/*
+/*	int	dns_lookup_x(name, type, rflags, list, fqdn, why, rcode, lflags)
+/*	const char *name;
+/*	unsigned type;
+/*	unsigned rflags;
+/*	DNS_RR	**list;
+/*	VSTRING *fqdn;
+/*	VSTRING *why;
+/*	int	*rcode;
+/*	unsigned lflags;
+/* DESCRIPTION
+/*	dns_lookup() looks up DNS resource records. When requested to
+/*	look up data other than type CNAME, it will follow a limited
+/*	number of CNAME indirections. All result names (including
+/*	null terminator) will fit a buffer of size DNS_NAME_LEN.
+/*	All name results are validated by \fIvalid_hostname\fR();
+/*	an invalid name is reported as a DNS_INVAL result, while
+/*	malformed replies are reported as transient errors.
+/*
+/*	dns_lookup_l() and dns_lookup_v() allow the user to specify
+/*	a list of resource types.
+/*
+/*	dns_lookup_x, dns_lookup_r(), dns_lookup_rl() and dns_lookup_rv()
+/*	accept or return additional information.
+/*
+/*	The var_dns_ncache_ttl_fix variable controls a workaround
+/*	for res_search(3) implementations that break the
+/*	DNS_REQ_FLAG_NCACHE_TTL feature. The workaround does not
+/*	support EDNS0 or DNSSEC, but it should be sufficient for
+/*	DNSBL/DNSWL lookups.
+/* INPUTS
+/* .ad
+/* .fi
+/* .IP name
+/*	The name to be looked up in the domain name system.
+/*	This name must pass the valid_hostname() test; it
+/*	must not be an IP address.
+/* .IP type
+/*	The resource record type to be looked up (T_A, T_MX etc.).
+/* .IP rflags
+/*	Resolver flags. These are a bitwise OR of:
+/* .RS
+/* .IP RES_DEBUG
+/*	Print debugging information.
+/* .IP RES_DNSRCH
+/*	Search local domain and parent domains.
+/* .IP RES_DEFNAMES
+/*	Append local domain to unqualified names.
+/* .IP RES_USE_DNSSEC
+/*	Request DNSSEC validation. This flag is silently ignored
+/*	when the system stub resolver API, resolver(3), does not
+/*	implement DNSSEC.
+/*	Automatically turns on the RES_TRUSTAD flag on systems that
+/*	support this flag (this behavior will be more configurable
+/*	in a later release).
+/* .RE
+/* .IP lflags
+/*	Flags that control the operation of the dns_lookup*()
+/*	functions.  DNS_REQ_FLAG_NONE requests no special processing.
+/*	Otherwise, specify one or more of the following:
+/* .RS
+/* .IP DNS_REQ_FLAG_STOP_INVAL
+/*	This flag is used by dns_lookup_l() and dns_lookup_v().
+/*	Invoke dns_lookup() for the resource types in the order as
+/*	specified, and return when dns_lookup() returns DNS_INVAL.
+/* .IP DNS_REQ_FLAG_STOP_NULLMX
+/*	This flag is used by dns_lookup_l() and dns_lookup_v().
+/*	Invoke dns_lookup() for the resource types in the order as
+/*	specified, and return when dns_lookup() returns DNS_NULLMX.
+/* .IP DNS_REQ_FLAG_STOP_MX_POLICY
+/*	This flag is used by dns_lookup_l() and dns_lookup_v().
+/*	Invoke dns_lookup() for the resource types in the order as
+/*	specified, and return when dns_lookup() returns DNS_POLICY
+/*	for an MX query.
+/* .IP DNS_REQ_FLAG_STOP_OK
+/*	This flag is used by dns_lookup_l() and dns_lookup_v().
+/*	Invoke dns_lookup() for the resource types in the order as
+/*	specified, and return when dns_lookup() returns DNS_OK.
+/* .IP DNS_REQ_FLAG_NCACHE_TTL
+/*	When the lookup result status is DNS_NOTFOUND, return the
+/*	SOA record(s) from the authority section in the reply, if
+/*	available. The per-record reply TTL specifies how long the
+/*	DNS_NOTFOUND answer is valid. The caller should pass the
+/*	record(s) to dns_rr_free().
+/*	Logs a warning if the RES_DNSRCH or RES_DEFNAMES resolver
+/*	flags are set, and disables those flags.
+/* .RE
+/* .IP ltype
+/*	The resource record types to be looked up. In the case of
+/*	dns_lookup_l(), this is a null-terminated argument list.
+/*	In the case of dns_lookup_v(), this is a null-terminated
+/*	integer array.
+/* OUTPUTS
+/* .ad
+/* .fi
+/* .IP list
+/*	A null pointer, or a pointer to a variable that receives a
+/*	list of requested resource records.
+/* .IP fqdn
+/*	A null pointer, or storage for the fully-qualified domain
+/*	name found for \fIname\fR.
+/* .IP why
+/*	A null pointer, or storage for the reason for failure.
+/* .IP rcode
+/*	Pointer to storage for the reply RCODE value. This gives
+/*	more detailed information than DNS_FAIL, DNS_RETRY, etc.
+/* DIAGNOSTICS
+/*	If DNSSEC validation is requested but the response is not
+/*	DNSSEC validated, dns_lookup() will send a one-time probe
+/*	query as configured with the \fBdnssec_probe\fR configuration
+/*	parameter, and will log a warning when the probe response
+/*	was not DNSSEC validated.
+/* .PP
+/*	dns_lookup() returns one of the following codes and sets the
+/*	\fIwhy\fR argument accordingly:
+/* .IP DNS_OK
+/*	The DNS query succeeded.
+/* .IP DNS_POLICY
+/*	The DNS query succeeded, but the answer did not pass the
+/*	policy filter.
+/* .IP DNS_NOTFOUND
+/*	The DNS query succeeded; the requested information was not found.
+/* .IP DNS_NULLMX
+/*	The DNS query succeeded; the requested service is unavailable.
+/*	This is returned when the list argument is not a null
+/*	pointer, and an MX lookup result contains a null server
+/*	name (so-called "nullmx" record).
+/* .IP DNS_INVAL
+/*	The DNS query succeeded; the result failed the valid_hostname() test.
+/*
+/*	NOTE: the valid_hostname() test is skipped for results that
+/*	the caller suppresses explicitly.  For example, when the
+/*	caller requests MX record lookup but specifies a null
+/*	resource record list argument, no syntax check will be done
+/*	for MX server names.
+/* .IP DNS_RETRY
+/*	The query failed, or the reply was malformed.
+/*	The problem is considered transient.
+/* .IP DNS_FAIL
+/*	The query failed.
+/* BUGS
+/*	dns_lookup() implements a subset of all possible resource types:
+/*	CNAME, MX, A, and some records with similar formatting requirements.
+/*	It is unwise to specify the T_ANY wildcard resource type.
+/*
+/*	It takes a surprising amount of code to accomplish what appears
+/*	to be a simple task. Later versions of the mail system may implement
+/*	their own DNS client software.
+/* SEE ALSO
+/*	dns_rr(3) resource record memory and list management
+/* LICENSE
+/* .ad
+/* .fi
+/*	The Secure Mailer license must be distributed with this software.
+/* AUTHOR(S)
+/*	Wietse Venema
+/*	IBM T.J. Watson Research
+/*	P.O. Box 704
+/*	Yorktown Heights, NY 10598, USA
+/*
+/*	Wietse Venema
+/*	Google, Inc.
+/*	111 8th Avenue
+/*	New York, NY 10011, USA
+/*--*/
+
+/* System library. */
+
+#include <sys_defs.h>
+#include <netdb.h>
+#include <string.h>
+#include <ctype.h>
+
+/* Utility library. */
+
+#include <mymalloc.h>
+#include <vstring.h>
+#include <msg.h>
+#include <valid_hostname.h>
+#include <stringops.h>
+
+/* Global library. */
+
+#include <mail_params.h>
+
+/* DNS library. */
+
+#define LIBDNS_INTERNAL
+#include "dns.h"
+
+/* Local stuff. */
+
+ /*
+  * Structure to keep track of things while decoding a name server reply.
+  */
+#define DEF_DNS_REPLY_SIZE	4096	/* in case we're using TCP */
+#define MAX_DNS_REPLY_SIZE	65536	/* in case we're using TCP */
+#define MAX_DNS_QUERY_SIZE	2048	/* XXX */
+
+typedef struct DNS_REPLY {
+    unsigned char *buf;			/* raw reply data */
+    size_t  buf_len;			/* reply buffer length */
+    int     rcode;			/* unfiltered reply code */
+    int     dnssec_ad;			/* DNSSEC AD bit */
+    int     query_count;		/* number of queries */
+    int     answer_count;		/* number of answers */
+    int     auth_count;			/* number of authority records */
+    unsigned char *query_start;		/* start of query data */
+    unsigned char *answer_start;	/* start of answer data */
+    unsigned char *end;			/* first byte past reply */
+} DNS_REPLY;
+
+ /*
+  * Test/set primitives to determine if the reply buffer contains a server
+  * response. We use this when the caller requests DNS_REQ_FLAG_NCACHE_TTL,
+  * and the DNS server replies that the requested record does not exist.
+  */
+#define TEST_HAVE_DNS_REPLY_PACKET(r)	((r)->end > (r)->buf)
+#define SET_HAVE_DNS_REPLY_PACKET(r, l)	((r)->end = (r)->buf + (l))
+#define SET_NO_DNS_REPLY_PACKET(r)	((r)->end = (r)->buf)
+
+#define INET_ADDR_LEN	4		/* XXX */
+#define INET6_ADDR_LEN	16		/* XXX */
+
+ /*
+  * To improve postscreen's whitelisting support, we need to know how long a
+  * DNSBL "not found" answer is valid. The 2010 implementation assumed it was
+  * valid for 3600 seconds. That is too long by 2015 standards.
+  * 
+  * Instead of guessing, Postfix 3.1 and later implement RFC 2308 (DNS NCACHE),
+  * where a DNS server provides the TTL of a "not found" response as the TTL
+  * of an SOA record in the authority section.
+  * 
+  * Unfortunately, the res_search() and res_query() API gets in the way. These
+  * functions overload their result value, the server reply length, and
+  * return -1 when the requested record does not exist. With libbind-based
+  * implementations, the server response is still available in an application
+  * buffer, thanks to the promise that res_query() and res_search() invoke
+  * res_send(), which returns the full server response even if the requested
+  * record does not exist.
+  * 
+  * If this promise is broken (for example, res_search() does not call
+  * res_send(), but some non-libbind implementation that updates the
+  * application buffer only when the requested record exists), then we have a
+  * way out by setting the var_dns_ncache_ttl_fix variable. This enables a
+  * limited res_query() clone that should be sufficient for DNSBL / DNSWL
+  * lookups.
+  * 
+  * The libunbound API does not comingle the reply length and reply status
+  * information, but that will have to wait until it is safe to make
+  * libunbound a mandatory dependency for Postfix.
+  */
+#ifdef HAVE_RES_SEND
+
+/* dns_res_query - a res_query() clone that can return negative replies */
+
+static int dns_res_query(const char *name, int class, int type,
+			         unsigned char *answer, int anslen)
+{
+    unsigned char msg_buf[MAX_DNS_QUERY_SIZE];
+    HEADER *reply_header = (HEADER *) answer;
+    int     len;
+
+    /*
+     * Differences with res_query() from libbind:
+     * 
+     * - This function returns a positive server reply length not only in case
+     * of success, but in all cases where a server reply is available that
+     * passes the preliminary checks in res_send().
+     * 
+     * - This function clears h_errno in case of success. The caller must use
+     * h_errno instead of the return value to decide if the lookup was
+     * successful.
+     * 
+     * - No support for EDNS0 and DNSSEC (including turning off EDNS0 after
+     * error). That should be sufficient for DNS reputation lookups where the
+     * reply contains a small number of IP addresses.  TXT records are out of
+     * scope for this workaround.
+     */
+    reply_header->rcode = NOERROR;
+
+#define NO_MKQUERY_DATA_BUF     ((unsigned char *) 0)
+#define NO_MKQUERY_DATA_LEN     ((int) 0)
+#define NO_MKQUERY_NEWRR        ((unsigned char *) 0)
+
+    if ((len = res_mkquery(QUERY, name, class, type, NO_MKQUERY_DATA_BUF,
+			   NO_MKQUERY_DATA_LEN, NO_MKQUERY_NEWRR,
+			   msg_buf, sizeof(msg_buf))) < 0) {
+	SET_H_ERRNO(NO_RECOVERY);
+	if (msg_verbose)
+	    msg_info("res_mkquery() failed");
+	return (len);
+    } else if ((len = res_send(msg_buf, len, answer, anslen)) < 0) {
+	SET_H_ERRNO(TRY_AGAIN);
+	if (msg_verbose)
+	    msg_info("res_send() failed");
+	return (len);
+    } else {
+	switch (reply_header->rcode) {
+	case NXDOMAIN:
+	    SET_H_ERRNO(HOST_NOT_FOUND);
+	    break;
+	case NOERROR:
+	    if (reply_header->ancount != 0)
+		SET_H_ERRNO(0);
+	    else
+		SET_H_ERRNO(NO_DATA);
+	    break;
+	case SERVFAIL:
+	    SET_H_ERRNO(TRY_AGAIN);
+	    break;
+	default:
+	    SET_H_ERRNO(NO_RECOVERY);
+	    break;
+	}
+	return (len);
+    }
+}
+
+#endif
+
+/* dns_res_search - res_search() that can return negative replies */
+
+static int dns_res_search(const char *name, int class, int type,
+	               unsigned char *answer, int anslen, int keep_notfound)
+{
+    int     len;
+
+    /*
+     * Differences with res_search() from libbind:
+     * 
+     * - With a non-zero keep_notfound argument, this function returns a
+     * positive server reply length not only in case of success, but also in
+     * case of a "notfound" reply status. The keep_notfound argument is
+     * usually zero, which allows us to avoid an unnecessary memset() call in
+     * the most common use case.
+     * 
+     * - This function clears h_errno in case of success. The caller must use
+     * h_errno instead of the return value to decide if a lookup was
+     * successful.
+     */
+#define NOT_FOUND_H_ERRNO(he) ((he) == HOST_NOT_FOUND || (he) == NO_DATA)
+
+    if (keep_notfound)
+	/* Prepare for returning a null-padded server reply. */
+	memset(answer, 0, anslen);
+    len = res_search(name, class, type, answer, anslen);
+    /* Begin API creep workaround. */
+    if (len < 0 && h_errno == 0) {
+	SET_H_ERRNO(TRY_AGAIN);
+	msg_warn("res_query(\"%s\", %d, %d, %p, %d) returns %d with h_errno==0"
+		 " -- setting h_errno=TRY_AGAIN",
+		 name, class, type, answer, anslen, len);
+    }
+    /* End API creep workaround. */
+    if (len > 0) {
+	SET_H_ERRNO(0);
+    } else if (keep_notfound && NOT_FOUND_H_ERRNO(h_errno)) {
+	/* Expect to return a null-padded server reply. */
+	len = anslen;
+    }
+    return (len);
+}
+
+/* dns_query - query name server and pre-parse the reply */
+
+static int dns_query(const char *name, int type, unsigned flags,
+		             DNS_REPLY *reply, VSTRING *why, unsigned lflags)
+{
+    HEADER *reply_header;
+    int     len;
+    unsigned long saved_options;
+    int     keep_notfound = (lflags & DNS_REQ_FLAG_NCACHE_TTL);
+
+    /*
+     * Initialize the reply buffer.
+     */
+    if (reply->buf == 0) {
+	reply->buf = (unsigned char *) mymalloc(DEF_DNS_REPLY_SIZE);
+	reply->buf_len = DEF_DNS_REPLY_SIZE;
+    }
+
+    /*
+     * Initialize the name service.
+     */
+    if ((_res.options & RES_INIT) == 0 && res_init() < 0) {
+	if (why)
+	    vstring_strcpy(why, "Name service initialization failure");
+	return (DNS_FAIL);
+    }
+
+    /*
+     * Set search options: debugging, parent domain search, append local
+     * domain. Do not allow the user to control other features.
+     */
+#define USER_FLAGS (RES_DEBUG | RES_DNSRCH | RES_DEFNAMES | RES_USE_DNSSEC)
+
+    if ((flags & USER_FLAGS) != flags)
+	msg_panic("dns_query: bad flags: %d", flags);
+
+    /*
+     * Set extra options that aren't exposed to the application.
+     */
+#define XTRA_FLAGS (RES_USE_EDNS0 | RES_TRUSTAD)
+
+    if (DNS_WANT_DNSSEC_VALIDATION(flags))
+	flags |= (RES_USE_EDNS0 | RES_TRUSTAD);
+
+    /*
+     * Can't append domains: we need the right SOA TTL.
+     */
+#define APPEND_DOMAIN_FLAGS (RES_DNSRCH | RES_DEFNAMES)
+
+    if (keep_notfound && (flags & APPEND_DOMAIN_FLAGS)) {
+	msg_warn("negative caching disables RES_DEFNAMES and RES_DNSRCH");
+	flags &= ~APPEND_DOMAIN_FLAGS;
+    }
+
+    /*
+     * Save and restore resolver options that we overwrite, to avoid
+     * surprising behavior in other code that also invokes the resolver.
+     */
+#define SAVE_FLAGS (USER_FLAGS | XTRA_FLAGS)
+
+    saved_options = (_res.options & SAVE_FLAGS);
+
+    /*
+     * Perform the lookup. Claim that the information cannot be found if and
+     * only if the name server told us so.
+     */
+    for (;;) {
+	_res.options &= ~saved_options;
+	_res.options |= flags;
+	if (keep_notfound && var_dns_ncache_ttl_fix) {
+#ifdef HAVE_RES_SEND
+	    len = dns_res_query((char *) name, C_IN, type, reply->buf,
+				reply->buf_len);
+#else
+	    var_dns_ncache_ttl_fix = 0;
+	    msg_warn("system library does not support %s=yes"
+		     " -- ignoring this setting", VAR_DNS_NCACHE_TTL_FIX);
+	    len = dns_res_search((char *) name, C_IN, type, reply->buf,
+				 reply->buf_len, keep_notfound);
+#endif
+	} else {
+	    len = dns_res_search((char *) name, C_IN, type, reply->buf,
+				 reply->buf_len, keep_notfound);
+	}
+	_res.options &= ~flags;
+	_res.options |= saved_options;
+	reply_header = (HEADER *) reply->buf;
+	reply->rcode = reply_header->rcode;
+	if ((reply->dnssec_ad = !!reply_header->ad) != 0)
+	    DNS_SEC_STATS_SET(DNS_SEC_FLAG_AVAILABLE);
+	if (h_errno != 0) {
+	    if (why)
+		vstring_sprintf(why, "Host or domain name not found. "
+				"Name service error for name=%s type=%s: %s",
+			    name, dns_strtype(type), dns_strerror(h_errno));
+	    if (msg_verbose)
+		msg_info("dns_query: %s (%s): %s",
+			 name, dns_strtype(type), dns_strerror(h_errno));
+	    switch (h_errno) {
+	    case NO_RECOVERY:
+		return (DNS_FAIL);
+	    case HOST_NOT_FOUND:
+	    case NO_DATA:
+		if (keep_notfound)
+		    break;
+		SET_NO_DNS_REPLY_PACKET(reply);
+		return (DNS_NOTFOUND);
+	    default:
+		return (DNS_RETRY);
+	    }
+	} else {
+	    if (msg_verbose)
+		msg_info("dns_query: %s (%s): OK", name, dns_strtype(type));
+	}
+
+	if (reply_header->tc == 0 || reply->buf_len >= MAX_DNS_REPLY_SIZE)
+	    break;
+	reply->buf = (unsigned char *)
+	    myrealloc((void *) reply->buf, 2 * reply->buf_len);
+	reply->buf_len *= 2;
+    }
+
+    /*
+     * Future proofing. If this reaches the panic call, then some code change
+     * introduced a bug.
+     */
+    if (len < 0)
+	msg_panic("dns_query: bad length %d (h_errno=%s)",
+		  len, dns_strerror(h_errno));
+
+    /*
+     * Paranoia.
+     */
+    if (len > reply->buf_len) {
+	msg_warn("reply length %d > buffer length %d for name=%s type=%s",
+		 len, (int) reply->buf_len, name, dns_strtype(type));
+	len = reply->buf_len;
+    }
+
+    /*
+     * Initialize the reply structure. Some structure members are filled on
+     * the fly while the reply is being parsed.
+     */
+    SET_HAVE_DNS_REPLY_PACKET(reply, len);
+    reply->query_start = reply->buf + sizeof(HEADER);
+    reply->answer_start = 0;
+    reply->query_count = ntohs(reply_header->qdcount);
+    reply->answer_count = ntohs(reply_header->ancount);
+    reply->auth_count = ntohs(reply_header->nscount);
+    if (msg_verbose > 1)
+	msg_info("dns_query: reply len=%d ancount=%d nscount=%d",
+		 len, reply->answer_count, reply->auth_count);
+
+    /*
+     * Future proofing. If this reaches the panic call, then some code change
+     * introduced a bug.
+     */
+    if (h_errno == 0) {
+	return (DNS_OK);
+    } else if (keep_notfound) {
+	return (DNS_NOTFOUND);
+    } else {
+	msg_panic("dns_query: unexpected reply status: %s",
+		  dns_strerror(h_errno));
+    }
+}
+
+/* dns_skip_query - skip query data in name server reply */
+
+static int dns_skip_query(DNS_REPLY *reply)
+{
+    int     query_count = reply->query_count;
+    unsigned char *pos = reply->query_start;
+    int     len;
+
+    /*
+     * For each query, skip over the domain name and over the fixed query
+     * data.
+     */
+    while (query_count-- > 0) {
+	if (pos >= reply->end)
+	    return DNS_RETRY;
+	len = dn_skipname(pos, reply->end);
+	if (len < 0)
+	    return (DNS_RETRY);
+	pos += len + QFIXEDSZ;
+    }
+    reply->answer_start = pos;
+    return (DNS_OK);
+}
+
+/* dns_get_fixed - extract fixed data from resource record */
+
+static int dns_get_fixed(unsigned char *pos, DNS_FIXED *fixed)
+{
+    GETSHORT(fixed->type, pos);
+    GETSHORT(fixed->class, pos);
+    GETLONG(fixed->ttl, pos);
+    GETSHORT(fixed->length, pos);
+
+    if (fixed->class != C_IN) {
+	msg_warn("dns_get_fixed: bad class: %u", fixed->class);
+	return (DNS_RETRY);
+    }
+    return (DNS_OK);
+}
+
+/* valid_rr_name - validate hostname in resource record */
+
+static int valid_rr_name(const char *name, const char *location,
+			         unsigned type, DNS_REPLY *reply)
+{
+    char    temp[DNS_NAME_LEN];
+    char   *query_name;
+    int     len;
+    char   *gripe;
+    int     result;
+
+    /*
+     * People aren't supposed to specify numeric names where domain names are
+     * required, but it "works" with some mailers anyway, so people complain
+     * when software doesn't bend over backwards.
+     */
+#define PASS_NAME	1
+#define REJECT_NAME	0
+
+    if (valid_hostaddr(name, DONT_GRIPE)) {
+	result = PASS_NAME;
+	gripe = "numeric domain name";
+    } else if (!valid_hostname(name, DO_GRIPE | DO_WILDCARD)) {
+	result = REJECT_NAME;
+	gripe = "malformed domain name";
+    } else {
+	result = PASS_NAME;
+	gripe = 0;
+    }
+
+    /*
+     * If we have a gripe, show some context, including the name used in the
+     * query and the type of reply that we're looking at.
+     */
+    if (gripe) {
+	len = dn_expand(reply->buf, reply->end, reply->query_start,
+			temp, DNS_NAME_LEN);
+	query_name = (len < 0 ? "*unparsable*" : temp);
+	msg_warn("%s in %s of %s record for %s: %.100s",
+		 gripe, location, dns_strtype(type), query_name, name);
+    }
+    return (result);
+}
+
+/* dns_get_rr - extract resource record from name server reply */
+
+static int dns_get_rr(DNS_RR **list, const char *orig_name, DNS_REPLY *reply,
+		              unsigned char *pos, char *rr_name,
+		              DNS_FIXED *fixed)
+{
+    char    temp[DNS_NAME_LEN];
+    char   *tempbuf = temp;
+    UINT32_TYPE soa_buf[5];
+    int     comp_len;
+    ssize_t data_len;
+    unsigned pref = 0;
+    unsigned char *src;
+    unsigned char *dst;
+    int     ch;
+
+#define MIN2(a, b)	((unsigned)(a) < (unsigned)(b) ? (a) : (b))
+
+    *list = 0;
+
+    switch (fixed->type) {
+    default:
+	msg_panic("dns_get_rr: don't know how to extract resource type %s",
+		  dns_strtype(fixed->type));
+    case T_CNAME:
+    case T_DNAME:
+    case T_MB:
+    case T_MG:
+    case T_MR:
+    case T_NS:
+    case T_PTR:
+	if (dn_expand(reply->buf, reply->end, pos, temp, sizeof(temp)) < 0)
+	    return (DNS_RETRY);
+	if (!valid_rr_name(temp, "resource data", fixed->type, reply))
+	    return (DNS_INVAL);
+	data_len = strlen(temp) + 1;
+	break;
+    case T_MX:
+	GETSHORT(pref, pos);
+	if (dn_expand(reply->buf, reply->end, pos, temp, sizeof(temp)) < 0)
+	    return (DNS_RETRY);
+	/* Don't even think of returning an invalid hostname to the caller. */
+	if (*temp == 0)
+	    return (DNS_NULLMX);		/* TODO: descriptive text */
+	if (!valid_rr_name(temp, "resource data", fixed->type, reply))
+	    return (DNS_INVAL);
+	data_len = strlen(temp) + 1;
+	break;
+    case T_A:
+	if (fixed->length != INET_ADDR_LEN) {
+	    msg_warn("extract_answer: bad address length: %d", fixed->length);
+	    return (DNS_RETRY);
+	}
+	if (fixed->length > sizeof(temp))
+	    msg_panic("dns_get_rr: length %d > DNS_NAME_LEN",
+		      fixed->length);
+	memcpy(temp, pos, fixed->length);
+	data_len = fixed->length;
+	break;
+#ifdef T_AAAA
+    case T_AAAA:
+	if (fixed->length != INET6_ADDR_LEN) {
+	    msg_warn("extract_answer: bad address length: %d", fixed->length);
+	    return (DNS_RETRY);
+	}
+	if (fixed->length > sizeof(temp))
+	    msg_panic("dns_get_rr: length %d > DNS_NAME_LEN",
+		      fixed->length);
+	memcpy(temp, pos, fixed->length);
+	data_len = fixed->length;
+	break;
+#endif
+
+	/*
+	 * We impose the same length limit here as for DNS names. However,
+	 * see T_TLSA discussion below.
+	 */
+    case T_TXT:
+	data_len = MIN2(pos[0] + 1, MIN2(fixed->length + 1, sizeof(temp)));
+	for (src = pos + 1, dst = (unsigned char *) (temp);
+	     dst < (unsigned char *) (temp) + data_len - 1; /* */ ) {
+	    ch = *src++;
+	    *dst++ = (ISPRINT(ch) ? ch : ' ');
+	}
+	*dst = 0;
+	break;
+
+	/*
+	 * For a full certificate, fixed->length may be longer than
+	 * sizeof(tmpbuf) == DNS_NAME_LEN.  Since we don't need a decode
+	 * buffer, just copy the raw data into the rr.
+	 * 
+	 * XXX Reject replies with bogus length < 3.
+	 * 
+	 * XXX What about enforcing a sane upper bound? The RFC 1035 hard
+	 * protocol limit is the RRDATA length limit of 65535.
+	 */
+    case T_TLSA:
+	data_len = fixed->length;
+	tempbuf = (char *) pos;
+	break;
+
+	/*
+	 * We use the SOA record TTL to determine the negative reply TTL. We
+	 * save the time fields in the SOA record for debugging, but for now
+	 * we don't bother saving the source host and mailbox information, as
+	 * that would require changes to the DNS_RR structure and APIs. See
+	 * also code in dns_strrecord().
+	 */
+    case T_SOA:
+	comp_len = dn_skipname(pos, reply->end);
+	if (comp_len < 0)
+	    return (DNS_RETRY);
+	pos += comp_len;
+	comp_len = dn_skipname(pos, reply->end);
+	if (comp_len < 0)
+	    return (DNS_RETRY);
+	pos += comp_len;
+	if (reply->end - pos < sizeof(soa_buf)) {
+	    msg_warn("extract_answer: bad SOA length: %d", fixed->length);
+	    return (DNS_RETRY);
+	}
+	GETLONG(soa_buf[0], pos);		/* Serial */
+	GETLONG(soa_buf[1], pos);		/* Refresh */
+	GETLONG(soa_buf[2], pos);		/* Retry */
+	GETLONG(soa_buf[3], pos);		/* Expire */
+	GETLONG(soa_buf[4], pos);		/* Ncache TTL */
+	tempbuf = (char *) soa_buf;
+	data_len = sizeof(soa_buf);
+	break;
+    }
+    *list = dns_rr_create(orig_name, rr_name, fixed->type, fixed->class,
+			  fixed->ttl, pref, tempbuf, data_len);
+    return (DNS_OK);
+}
+
+/* dns_get_alias - extract CNAME from name server reply */
+
+static int dns_get_alias(DNS_REPLY *reply, unsigned char *pos,
+			         DNS_FIXED *fixed, char *cname, int c_len)
+{
+    if (fixed->type != T_CNAME)
+	msg_panic("dns_get_alias: bad type %s", dns_strtype(fixed->type));
+    if (dn_expand(reply->buf, reply->end, pos, cname, c_len) < 0)
+	return (DNS_RETRY);
+    if (!valid_rr_name(cname, "resource data", fixed->type, reply))
+	return (DNS_INVAL);
+    return (DNS_OK);
+}
+
+/* dns_get_answer - extract answers from name server reply */
+
+static int dns_get_answer(const char *orig_name, DNS_REPLY *reply, int type,
+	             DNS_RR **rrlist, VSTRING *fqdn, char *cname, int c_len,
+			          int *maybe_secure)
+{
+    char    rr_name[DNS_NAME_LEN];
+    unsigned char *pos;
+    int     answer_count = reply->answer_count;
+    int     len;
+    DNS_FIXED fixed;
+    DNS_RR *rr;
+    int     resource_found = 0;
+    int     cname_found = 0;
+    int     not_found_status = DNS_NOTFOUND;	/* can't happen */
+    int     status;
+
+    /*
+     * Initialize. Skip over the name server query if we haven't yet.
+     */
+    if (reply->answer_start == 0)
+	if ((status = dns_skip_query(reply)) < 0)
+	    return (status);
+    pos = reply->answer_start;
+
+    /*
+     * Either this, or use a GOTO for emergency exits. The purpose is to
+     * prevent incomplete answers from being passed back to the caller.
+     */
+#define CORRUPT(status) { \
+	if (rrlist && *rrlist) { \
+	    dns_rr_free(*rrlist); \
+	    *rrlist = 0; \
+	} \
+	return (status); \
+    }
+
+    /*
+     * Iterate over all answers.
+     */
+    while (answer_count-- > 0) {
+
+	/*
+	 * Optionally extract the fully-qualified domain name.
+	 */
+	if (pos >= reply->end)
+	    CORRUPT(DNS_RETRY);
+	len = dn_expand(reply->buf, reply->end, pos, rr_name, DNS_NAME_LEN);
+	if (len < 0)
+	    CORRUPT(DNS_RETRY);
+	pos += len;
+
+	/*
+	 * Extract the fixed reply data: type, class, ttl, length.
+	 */
+	if (pos + RRFIXEDSZ > reply->end)
+	    CORRUPT(DNS_RETRY);
+	if ((status = dns_get_fixed(pos, &fixed)) != DNS_OK)
+	    CORRUPT(status);
+	if (strcmp(orig_name, ".") == 0 && *rr_name == 0)
+	     /* Allow empty response name for root queries. */ ;
+	else if (!valid_rr_name(rr_name, "resource name", fixed.type, reply))
+	    CORRUPT(DNS_INVAL);
+	if (fqdn)
+	    vstring_strcpy(fqdn, rr_name);
+	if (msg_verbose)
+	    msg_info("dns_get_answer: type %s for %s",
+		     dns_strtype(fixed.type), rr_name);
+	pos += RRFIXEDSZ;
+
+	/*
+	 * Optionally extract the requested resource or CNAME data.
+	 */
+	if (pos + fixed.length > reply->end)
+	    CORRUPT(DNS_RETRY);
+	if (type == fixed.type || type == T_ANY) {	/* requested type */
+	    if (rrlist) {
+		if ((status = dns_get_rr(&rr, orig_name, reply, pos, rr_name,
+					 &fixed)) == DNS_OK) {
+		    resource_found++;
+		    rr->dnssec_valid = *maybe_secure ? reply->dnssec_ad : 0;
+		    *rrlist = dns_rr_append(*rrlist, rr);
+		} else if (status == DNS_NULLMX) {
+		    CORRUPT(status);		/* TODO: use better name */
+		} else if (not_found_status != DNS_RETRY)
+		    not_found_status = status;
+	    } else
+		resource_found++;
+	} else if (fixed.type == T_CNAME) {	/* cname resource */
+	    cname_found++;
+	    if (cname && c_len > 0)
+		if ((status = dns_get_alias(reply, pos, &fixed, cname, c_len)) != DNS_OK)
+		    CORRUPT(status);
+	    if (!reply->dnssec_ad)
+		*maybe_secure = 0;
+	}
+	pos += fixed.length;
+    }
+
+    /*
+     * See what answer we came up with. Report success when the requested
+     * information was found. Otherwise, when a CNAME was found, report that
+     * more recursion is needed. Otherwise report failure.
+     */
+    if (resource_found)
+	return (DNS_OK);
+    if (cname_found)
+	return (DNS_RECURSE);
+    return (not_found_status);
+}
+
+/* dns_lookup_x - DNS lookup user interface */
+
+int     dns_lookup_x(const char *name, unsigned type, unsigned flags,
+		             DNS_RR **rrlist, VSTRING *fqdn, VSTRING *why,
+		             int *rcode, unsigned lflags)
+{
+    char    cname[DNS_NAME_LEN];
+    int     c_len = sizeof(cname);
+    static DNS_REPLY reply;
+    int     count;
+    int     status;
+    int     maybe_secure = 1;		/* Query name presumed secure */
+    const char *orig_name = name;
+
+    /*
+     * Reset results early. DNS_OK is not the only status that returns
+     * resource records; DNS_NOTFOUND will do that too, if requested.
+     */
+    if (rrlist)
+	*rrlist = 0;
+
+    /*
+     * DJBDNS produces a bogus A record when given a numerical hostname.
+     */
+    if (valid_hostaddr(name, DONT_GRIPE)) {
+	if (why)
+	    vstring_sprintf(why,
+		   "Name service error for %s: invalid host or domain name",
+			    name);
+	if (rcode)
+	    *rcode = NXDOMAIN;
+	SET_H_ERRNO(HOST_NOT_FOUND);
+	return (DNS_NOTFOUND);
+    }
+
+    /*
+     * The Linux resolver misbehaves when given an invalid domain name.
+     */
+    if (strcmp(name, ".") && !valid_hostname(name, DONT_GRIPE | DO_WILDCARD)) {
+	if (why)
+	    vstring_sprintf(why,
+		   "Name service error for %s: invalid host or domain name",
+			    name);
+	if (rcode)
+	    *rcode = NXDOMAIN;
+	SET_H_ERRNO(HOST_NOT_FOUND);
+	return (DNS_NOTFOUND);
+    }
+
+    /*
+     * Perform the lookup. Follow CNAME chains, but only up to a
+     * pre-determined maximum.
+     */
+    for (count = 0; count < 10; count++) {
+
+	/*
+	 * Perform the DNS lookup, and pre-parse the name server reply.
+	 */
+	status = dns_query(name, type, flags, &reply, why, lflags);
+	if (rcode)
+	    *rcode = reply.rcode;
+	if (status != DNS_OK) {
+
+	    /*
+	     * If the record does not exist, and we have a copy of the server
+	     * response, try to extract the negative caching TTL for the SOA
+	     * record in the authority section. DO NOT return an error if an
+	     * SOA record is malformed.
+	     */
+	    if (status == DNS_NOTFOUND && TEST_HAVE_DNS_REPLY_PACKET(&reply)
+		&& reply.auth_count > 0) {
+		reply.answer_count = reply.auth_count;	/* XXX TODO: Fix API */
+		(void) dns_get_answer(orig_name, &reply, T_SOA, rrlist, fqdn,
+				      cname, c_len, &maybe_secure);
+	    }
+	    if (DNS_WANT_DNSSEC_VALIDATION(flags)
+		&& !DNS_SEC_STATS_TEST(DNS_SEC_FLAG_AVAILABLE | \
+				       DNS_SEC_FLAG_DONT_PROBE))
+		dns_sec_probe(flags);		/* XXX Clobbers 'reply' */
+	    return (status);
+	}
+
+	/*
+	 * Extract resource records of the requested type. Pick up CNAME
+	 * information just in case the requested data is not found.
+	 */
+	status = dns_get_answer(orig_name, &reply, type, rrlist, fqdn,
+				cname, c_len, &maybe_secure);
+	if (DNS_WANT_DNSSEC_VALIDATION(flags)
+	    && !DNS_SEC_STATS_TEST(DNS_SEC_FLAG_AVAILABLE | \
+				   DNS_SEC_FLAG_DONT_PROBE))
+	    dns_sec_probe(flags);		/* XXX Clobbers 'reply' */
+	switch (status) {
+	default:
+	    if (why)
+		vstring_sprintf(why, "Name service error for name=%s type=%s: "
+				"Malformed or unexpected name server reply",
+				name, dns_strtype(type));
+	    return (status);
+	case DNS_NULLMX:
+	    if (why)
+		vstring_sprintf(why, "Domain %s does not accept mail (nullMX)",
+				name);
+	    SET_H_ERRNO(NO_DATA);
+	    return (status);
+	case DNS_OK:
+	    if (rrlist && dns_rr_filter_maps) {
+		if (dns_rr_filter_execute(rrlist) < 0) {
+		    if (why)
+			vstring_sprintf(why,
+					"Error looking up name=%s type=%s: "
+					"Invalid DNS reply filter syntax",
+					name, dns_strtype(type));
+		    dns_rr_free(*rrlist);
+		    *rrlist = 0;
+		    status = DNS_RETRY;
+		} else if (*rrlist == 0) {
+		    if (why)
+			vstring_sprintf(why,
+					"Error looking up name=%s type=%s: "
+					"DNS reply filter drops all results",
+					name, dns_strtype(type));
+		    status = DNS_POLICY;
+		}
+	    }
+	    return (status);
+	case DNS_RECURSE:
+	    if (msg_verbose)
+		msg_info("dns_lookup: %s aliased to %s", name, cname);
+#if RES_USE_DNSSEC
+
+	    /*
+	     * Once an intermediate CNAME reply is not validated, all
+	     * consequent RRs are deemed not validated, so we don't ask for
+	     * further DNSSEC replies.
+	     */
+	    if (maybe_secure == 0)
+		flags &= ~RES_USE_DNSSEC;
+#endif
+	    name = cname;
+	}
+    }
+    if (why)
+	vstring_sprintf(why, "Name server loop for %s", name);
+    msg_warn("dns_lookup: Name server loop for %s", name);
+    return (DNS_NOTFOUND);
+}
+
+/* dns_lookup_rl - DNS lookup interface with types list */
+
+int     dns_lookup_rl(const char *name, unsigned flags, DNS_RR **rrlist,
+		              VSTRING *fqdn, VSTRING *why, int *rcode,
+		              int lflags,...)
+{
+    va_list ap;
+    unsigned type, next;
+    int     status = DNS_NOTFOUND;
+    int     hpref_status = INT_MIN;
+    VSTRING *hpref_rtext = 0;
+    int     hpref_rcode;
+    int     hpref_h_errno;
+    DNS_RR *rr;
+
+    /* Save intermediate highest-priority result. */
+#define SAVE_HPREF_STATUS() do { \
+	hpref_status = status; \
+	if (rcode) \
+	    hpref_rcode = *rcode; \
+	if (why && status != DNS_OK) \
+	    vstring_strcpy(hpref_rtext ? hpref_rtext : \
+			   (hpref_rtext = vstring_alloc(VSTRING_LEN(why))), \
+			   vstring_str(why)); \
+	hpref_h_errno = h_errno; \
+    } while (0)
+
+    /* Restore intermediate highest-priority result. */
+#define RESTORE_HPREF_STATUS() do { \
+	status = hpref_status; \
+	if (rcode) \
+	    *rcode = hpref_rcode; \
+	if (why && status != DNS_OK) \
+	    vstring_strcpy(why, vstring_str(hpref_rtext)); \
+	SET_H_ERRNO(hpref_h_errno); \
+    } while (0)
+
+    if (rrlist)
+	*rrlist = 0;
+    va_start(ap, lflags);
+    for (type = va_arg(ap, unsigned); type != 0; type = next) {
+	next = va_arg(ap, unsigned);
+	if (msg_verbose)
+	    msg_info("lookup %s type %s flags %s",
+		     name, dns_strtype(type), dns_str_resflags(flags));
+	status = dns_lookup_x(name, type, flags, rrlist ? &rr : (DNS_RR **) 0,
+			      fqdn, why, rcode, lflags);
+	if (rrlist && rr)
+	    *rrlist = dns_rr_append(*rrlist, rr);
+	if (status == DNS_OK) {
+	    if (lflags & DNS_REQ_FLAG_STOP_OK)
+		break;
+	} else if (status == DNS_INVAL) {
+	    if (lflags & DNS_REQ_FLAG_STOP_INVAL)
+		break;
+	} else if (status == DNS_POLICY) {
+	    if (type == T_MX && (lflags & DNS_REQ_FLAG_STOP_MX_POLICY))
+		break;
+	} else if (status == DNS_NULLMX) {
+	    if (lflags & DNS_REQ_FLAG_STOP_NULLMX)
+		break;
+	}
+	/* XXX Stop after NXDOMAIN error. */
+	if (next == 0)
+	    break;
+	if (status >= hpref_status)
+	    SAVE_HPREF_STATUS();		/* save last info */
+    }
+    va_end(ap);
+    if (status < hpref_status)
+	RESTORE_HPREF_STATUS();			/* else report last info */
+    if (hpref_rtext)
+	vstring_free(hpref_rtext);
+    return (status);
+}
+
+/* dns_lookup_rv - DNS lookup interface with types vector */
+
+int     dns_lookup_rv(const char *name, unsigned flags, DNS_RR **rrlist,
+		              VSTRING *fqdn, VSTRING *why, int *rcode,
+		              int lflags, unsigned *types)
+{
+    unsigned type, next;
+    int     status = DNS_NOTFOUND;
+    int     hpref_status = INT_MIN;
+    VSTRING *hpref_rtext = 0;
+    int     hpref_rcode;
+    int     hpref_h_errno;
+    DNS_RR *rr;
+
+    if (rrlist)
+	*rrlist = 0;
+    for (type = *types++; type != 0; type = next) {
+	next = *types++;
+	if (msg_verbose)
+	    msg_info("lookup %s type %s flags %s",
+		     name, dns_strtype(type), dns_str_resflags(flags));
+	status = dns_lookup_x(name, type, flags, rrlist ? &rr : (DNS_RR **) 0,
+			      fqdn, why, rcode, lflags);
+	if (rrlist && rr)
+	    *rrlist = dns_rr_append(*rrlist, rr);
+	if (status == DNS_OK) {
+	    if (lflags & DNS_REQ_FLAG_STOP_OK)
+		break;
+	} else if (status == DNS_INVAL) {
+	    if (lflags & DNS_REQ_FLAG_STOP_INVAL)
+		break;
+	} else if (status == DNS_POLICY) {
+	    if (type == T_MX && (lflags & DNS_REQ_FLAG_STOP_MX_POLICY))
+		break;
+	} else if (status == DNS_NULLMX) {
+	    if (lflags & DNS_REQ_FLAG_STOP_NULLMX)
+		break;
+	}
+	/* XXX Stop after NXDOMAIN error. */
+	if (next == 0)
+	    break;
+	if (status >= hpref_status)
+	    SAVE_HPREF_STATUS();		/* save last info */
+    }
+    if (status < hpref_status)
+	RESTORE_HPREF_STATUS();			/* else report last info */
+    if (hpref_rtext)
+	vstring_free(hpref_rtext);
+    return (status);
+}