PostgreSQL/src/backend/libpq/be-secure-openssl.c

/*-------------------------------------------------------------------------
 *
 * be-secure-openssl.c
 *	  functions for OpenSSL support in the backend.
 *
 *
 * Portions Copyright (c) 1996-2015, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  src/backend/libpq/be-secure-openssl.c
 *
 *	  Since the server static private key ($DataDir/server.key)
 *	  will normally be stored unencrypted so that the database
 *	  backend can restart automatically, it is important that
 *	  we select an algorithm that continues to provide confidentiality
 *	  even if the attacker has the server's private key.  Ephemeral
 *	  DH (EDH) keys provide this and more (Perfect Forward Secrecy
 *	  aka PFS).
 *
 *	  N.B., the static private key should still be protected to
 *	  the largest extent possible, to minimize the risk of
 *	  impersonations.
 *
 *	  Another benefit of EDH is that it allows the backend and
 *	  clients to use DSA keys.  DSA keys can only provide digital
 *	  signatures, not encryption, and are often acceptable in
 *	  jurisdictions where RSA keys are unacceptable.
 *
 *	  The downside to EDH is that it makes it impossible to
 *	  use ssldump(1) if there's a problem establishing an SSL
 *	  session.  In this case you'll need to temporarily disable
 *	  EDH by commenting out the callback.
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include <sys/stat.h>
#include <signal.h>
#include <fcntl.h>
#include <ctype.h>
#include <sys/socket.h>
#include <unistd.h>
#include <netdb.h>
#include <netinet/in.h>
#ifdef HAVE_NETINET_TCP_H
#include <netinet/tcp.h>
#include <arpa/inet.h>
#endif

#include <openssl/ssl.h>
#include <openssl/dh.h>
#if SSLEAY_VERSION_NUMBER >= 0x0907000L
#include <openssl/conf.h>
#endif
#if (OPENSSL_VERSION_NUMBER >= 0x0090800fL) && !defined(OPENSSL_NO_ECDH)
#include <openssl/ec.h>
#endif

#include "libpq/libpq.h"
#include "miscadmin.h"
#include "storage/latch.h"
#include "tcop/tcopprot.h"
#include "utils/memutils.h"


static int	my_sock_read(BIO *h, char *buf, int size);
static int	my_sock_write(BIO *h, const char *buf, int size);
static BIO_METHOD *my_BIO_s_socket(void);
static int	my_SSL_set_fd(Port *port, int fd);

static DH  *load_dh_file(int keylength);
static DH  *load_dh_buffer(const char *, size_t);
static DH  *tmp_dh_cb(SSL *s, int is_export, int keylength);
static int	verify_cb(int, X509_STORE_CTX *);
static void info_cb(const SSL *ssl, int type, int args);
static void initialize_ecdh(void);
static const char *SSLerrmessage(void);

static char *X509_NAME_to_cstring(X509_NAME *name);

static SSL_CTX *SSL_context = NULL;

/* ------------------------------------------------------------ */
/*						 Hardcoded values						*/
/* ------------------------------------------------------------ */

/*
 *	Hardcoded DH parameters, used in ephemeral DH keying.
 *	As discussed above, EDH protects the confidentiality of
 *	sessions even if the static private key is compromised,
 *	so we are *highly* motivated to ensure that we can use
 *	EDH even if the DBA... or an attacker... deletes the
 *	$DataDir/dh*.pem files.
 *
 *	We could refuse SSL connections unless a good DH parameter
 *	file exists, but some clients may quietly renegotiate an
 *	unsecured connection without fully informing the user.
 *	Very uncool.
 *
 *	Alternatively, the backend could attempt to load these files
 *	on startup if SSL is enabled - and refuse to start if any
 *	do not exist - but this would tend to piss off DBAs.
 *
 *	If you want to create your own hardcoded DH parameters
 *	for fun and profit, review "Assigned Number for SKIP
 *	Protocols" (http://www.skip-vpn.org/spec/numbers.html)
 *	for suggestions.
 */

static const char file_dh512[] =
"-----BEGIN DH PARAMETERS-----\n\
MEYCQQD1Kv884bEpQBgRjXyEpwpy1obEAxnIByl6ypUM2Zafq9AKUJsCRtMIPWak\n\
XUGfnHy9iUsiGSa6q6Jew1XpKgVfAgEC\n\
-----END DH PARAMETERS-----\n";

static const char file_dh1024[] =
"-----BEGIN DH PARAMETERS-----\n\
MIGHAoGBAPSI/VhOSdvNILSd5JEHNmszbDgNRR0PfIizHHxbLY7288kjwEPwpVsY\n\
jY67VYy4XTjTNP18F1dDox0YbN4zISy1Kv884bEpQBgRjXyEpwpy1obEAxnIByl6\n\
ypUM2Zafq9AKUJsCRtMIPWakXUGfnHy9iUsiGSa6q6Jew1XpL3jHAgEC\n\
-----END DH PARAMETERS-----\n";

static const char file_dh2048[] =
"-----BEGIN DH PARAMETERS-----\n\
MIIBCAKCAQEA9kJXtwh/CBdyorrWqULzBej5UxE5T7bxbrlLOCDaAadWoxTpj0BV\n\
89AHxstDqZSt90xkhkn4DIO9ZekX1KHTUPj1WV/cdlJPPT2N286Z4VeSWc39uK50\n\
T8X8dryDxUcwYc58yWb/Ffm7/ZFexwGq01uejaClcjrUGvC/RgBYK+X0iP1YTknb\n\
zSC0neSRBzZrM2w4DUUdD3yIsxx8Wy2O9vPJI8BD8KVbGI2Ou1WMuF040zT9fBdX\n\
Q6MdGGzeMyEstSr/POGxKUAYEY18hKcKctaGxAMZyAcpesqVDNmWn6vQClCbAkbT\n\
CD1mpF1Bn5x8vYlLIhkmuquiXsNV6TILOwIBAg==\n\
-----END DH PARAMETERS-----\n";

static const char file_dh4096[] =
"-----BEGIN DH PARAMETERS-----\n\
MIICCAKCAgEA+hRyUsFN4VpJ1O8JLcCo/VWr19k3BCgJ4uk+d+KhehjdRqNDNyOQ\n\
l/MOyQNQfWXPeGKmOmIig6Ev/nm6Nf9Z2B1h3R4hExf+zTiHnvVPeRBhjdQi81rt\n\
Xeoh6TNrSBIKIHfUJWBh3va0TxxjQIs6IZOLeVNRLMqzeylWqMf49HsIXqbcokUS\n\
Vt1BkvLdW48j8PPv5DsKRN3tloTxqDJGo9tKvj1Fuk74A+Xda1kNhB7KFlqMyN98\n\
VETEJ6c7KpfOo30mnK30wqw3S8OtaIR/maYX72tGOno2ehFDkq3pnPtEbD2CScxc\n\
alJC+EL7RPk5c/tgeTvCngvc1KZn92Y//EI7G9tPZtylj2b56sHtMftIoYJ9+ODM\n\
sccD5Piz/rejE3Ome8EOOceUSCYAhXn8b3qvxVI1ddd1pED6FHRhFvLrZxFvBEM9\n\
ERRMp5QqOaHJkM+Dxv8Cj6MqrCbfC4u+ZErxodzuusgDgvZiLF22uxMZbobFWyte\n\
OvOzKGtwcTqO/1wV5gKkzu1ZVswVUQd5Gg8lJicwqRWyyNRczDDoG9jVDxmogKTH\n\
AaqLulO7R8Ifa1SwF2DteSGVtgWEN8gDpN3RBmmPTDngyF2DHb5qmpnznwtFKdTL\n\
KWbuHn491xNO25CQWMtem80uKw+pTnisBRF/454n1Jnhub144YRBoN8CAQI=\n\
-----END DH PARAMETERS-----\n";


/* ------------------------------------------------------------ */
/*						 Public interface						*/
/* ------------------------------------------------------------ */

/*
 *	Initialize global SSL context.
 */
void
be_tls_init(void)
{
	struct stat buf;

	STACK_OF(X509_NAME) *root_cert_list = NULL;

	if (!SSL_context)
	{
#if SSLEAY_VERSION_NUMBER >= 0x0907000L
		OPENSSL_config(NULL);
#endif
		SSL_library_init();
		SSL_load_error_strings();

		/*
		 * We use SSLv23_method() because it can negotiate use of the highest
		 * mutually supported protocol version, while alternatives like
		 * TLSv1_2_method() permit only one specific version.  Note that we
		 * don't actually allow SSL v2 or v3, only TLS protocols (see below).
		 */
		SSL_context = SSL_CTX_new(SSLv23_method());
		if (!SSL_context)
			ereport(FATAL,
					(errmsg("could not create SSL context: %s",
							SSLerrmessage())));

		/*
		 * Disable OpenSSL's moving-write-buffer sanity check, because it
		 * causes unnecessary failures in nonblocking send cases.
		 */
		SSL_CTX_set_mode(SSL_context, SSL_MODE_ACCEPT_MOVING_WRITE_BUFFER);

		/*
		 * Load and verify server's certificate and private key
		 */
		if (SSL_CTX_use_certificate_chain_file(SSL_context,
											   ssl_cert_file) != 1)
			ereport(FATAL,
					(errcode(ERRCODE_CONFIG_FILE_ERROR),
				  errmsg("could not load server certificate file \"%s\": %s",
						 ssl_cert_file, SSLerrmessage())));

		if (stat(ssl_key_file, &buf) != 0)
			ereport(FATAL,
					(errcode_for_file_access(),
					 errmsg("could not access private key file \"%s\": %m",
							ssl_key_file)));

		/*
		 * Require no public access to key file.
		 *
		 * XXX temporarily suppress check when on Windows, because there may
		 * not be proper support for Unix-y file permissions.  Need to think
		 * of a reasonable check to apply on Windows.  (See also the data
		 * directory permission check in postmaster.c)
		 */
#if !defined(WIN32) && !defined(__CYGWIN__)
		if (!S_ISREG(buf.st_mode) || buf.st_mode & (S_IRWXG | S_IRWXO))
			ereport(FATAL,
					(errcode(ERRCODE_CONFIG_FILE_ERROR),
				  errmsg("private key file \"%s\" has group or world access",
						 ssl_key_file),
				   errdetail("Permissions should be u=rw (0600) or less.")));
#endif

		if (SSL_CTX_use_PrivateKey_file(SSL_context,
										ssl_key_file,
										SSL_FILETYPE_PEM) != 1)
			ereport(FATAL,
					(errmsg("could not load private key file \"%s\": %s",
							ssl_key_file, SSLerrmessage())));

		if (SSL_CTX_check_private_key(SSL_context) != 1)
			ereport(FATAL,
					(errmsg("check of private key failed: %s",
							SSLerrmessage())));
	}

	/* set up ephemeral DH keys, and disallow SSL v2/v3 while at it */
	SSL_CTX_set_tmp_dh_callback(SSL_context, tmp_dh_cb);
	SSL_CTX_set_options(SSL_context,
						SSL_OP_SINGLE_DH_USE |
						SSL_OP_NO_SSLv2 | SSL_OP_NO_SSLv3);

	/* set up ephemeral ECDH keys */
	initialize_ecdh();

	/* set up the allowed cipher list */
	if (SSL_CTX_set_cipher_list(SSL_context, SSLCipherSuites) != 1)
		elog(FATAL, "could not set the cipher list (no valid ciphers available)");

	/* Let server choose order */
	if (SSLPreferServerCiphers)
		SSL_CTX_set_options(SSL_context, SSL_OP_CIPHER_SERVER_PREFERENCE);

	/*
	 * Load CA store, so we can verify client certificates if needed.
	 */
	if (ssl_ca_file[0])
	{
		if (SSL_CTX_load_verify_locations(SSL_context, ssl_ca_file, NULL) != 1 ||
			(root_cert_list = SSL_load_client_CA_file(ssl_ca_file)) == NULL)
			ereport(FATAL,
					(errmsg("could not load root certificate file \"%s\": %s",
							ssl_ca_file, SSLerrmessage())));
	}

	/*----------
	 * Load the Certificate Revocation List (CRL).
	 * http://searchsecurity.techtarget.com/sDefinition/0,,sid14_gci803160,00.html
	 *----------
	 */
	if (ssl_crl_file[0])
	{
		X509_STORE *cvstore = SSL_CTX_get_cert_store(SSL_context);

		if (cvstore)
		{
			/* Set the flags to check against the complete CRL chain */
			if (X509_STORE_load_locations(cvstore, ssl_crl_file, NULL) == 1)
			{
				/* OpenSSL 0.96 does not support X509_V_FLAG_CRL_CHECK */
#ifdef X509_V_FLAG_CRL_CHECK
				X509_STORE_set_flags(cvstore,
						  X509_V_FLAG_CRL_CHECK | X509_V_FLAG_CRL_CHECK_ALL);
#else
				ereport(LOG,
				(errmsg("SSL certificate revocation list file \"%s\" ignored",
						ssl_crl_file),
				 errdetail("SSL library does not support certificate revocation lists.")));
#endif
			}
			else
				ereport(FATAL,
						(errmsg("could not load SSL certificate revocation list file \"%s\": %s",
								ssl_crl_file, SSLerrmessage())));
		}
	}

	if (ssl_ca_file[0])
	{
		/*
		 * Always ask for SSL client cert, but don't fail if it's not
		 * presented.  We might fail such connections later, depending on what
		 * we find in pg_hba.conf.
		 */
		SSL_CTX_set_verify(SSL_context,
						   (SSL_VERIFY_PEER |
							SSL_VERIFY_CLIENT_ONCE),
						   verify_cb);

		/* Set flag to remember CA store is successfully loaded */
		ssl_loaded_verify_locations = true;

		/*
		 * Tell OpenSSL to send the list of root certs we trust to clients in
		 * CertificateRequests.  This lets a client with a keystore select the
		 * appropriate client certificate to send to us.
		 */
		SSL_CTX_set_client_CA_list(SSL_context, root_cert_list);
	}
}

/*
 *	Attempt to negotiate SSL connection.
 */
int
be_tls_open_server(Port *port)
{
	int			r;
	int			err;
	int			waitfor;

	Assert(!port->ssl);
	Assert(!port->peer);

	if (!(port->ssl = SSL_new(SSL_context)))
	{
		ereport(COMMERROR,
				(errcode(ERRCODE_PROTOCOL_VIOLATION),
				 errmsg("could not initialize SSL connection: %s",
						SSLerrmessage())));
		return -1;
	}
	if (!my_SSL_set_fd(port, port->sock))
	{
		ereport(COMMERROR,
				(errcode(ERRCODE_PROTOCOL_VIOLATION),
				 errmsg("could not set SSL socket: %s",
						SSLerrmessage())));
		return -1;
	}
	port->ssl_in_use = true;

aloop:
	r = SSL_accept(port->ssl);
	if (r <= 0)
	{
		err = SSL_get_error(port->ssl, r);
		switch (err)
		{
			case SSL_ERROR_WANT_READ:
			case SSL_ERROR_WANT_WRITE:
				/* not allowed during connection establishment */
				Assert(!port->noblock);

				/*
				 * No need to care about timeouts/interrupts here. At this
				 * point authentication_timeout still employs
				 * StartupPacketTimeoutHandler() which directly exits.
				 */
				if (err == SSL_ERROR_WANT_READ)
					waitfor = WL_SOCKET_READABLE;
				else
					waitfor = WL_SOCKET_WRITEABLE;

				WaitLatchOrSocket(MyLatch, waitfor, port->sock, 0);
				goto aloop;
			case SSL_ERROR_SYSCALL:
				if (r < 0)
					ereport(COMMERROR,
							(errcode_for_socket_access(),
							 errmsg("could not accept SSL connection: %m")));
				else
					ereport(COMMERROR,
							(errcode(ERRCODE_PROTOCOL_VIOLATION),
					errmsg("could not accept SSL connection: EOF detected")));
				break;
			case SSL_ERROR_SSL:
				ereport(COMMERROR,
						(errcode(ERRCODE_PROTOCOL_VIOLATION),
						 errmsg("could not accept SSL connection: %s",
								SSLerrmessage())));
				break;
			case SSL_ERROR_ZERO_RETURN:
				ereport(COMMERROR,
						(errcode(ERRCODE_PROTOCOL_VIOLATION),
				   errmsg("could not accept SSL connection: EOF detected")));
				break;
			default:
				ereport(COMMERROR,
						(errcode(ERRCODE_PROTOCOL_VIOLATION),
						 errmsg("unrecognized SSL error code: %d",
								err)));
				break;
		}
		return -1;
	}

	port->count = 0;

	/* Get client certificate, if available. */
	port->peer = SSL_get_peer_certificate(port->ssl);

	/* and extract the Common Name from it. */
	port->peer_cn = NULL;
	port->peer_cert_valid = false;
	if (port->peer != NULL)
	{
		int			len;

		len = X509_NAME_get_text_by_NID(X509_get_subject_name(port->peer),
										NID_commonName, NULL, 0);
		if (len != -1)
		{
			char	   *peer_cn;

			peer_cn = MemoryContextAlloc(TopMemoryContext, len + 1);
			r = X509_NAME_get_text_by_NID(X509_get_subject_name(port->peer),
										  NID_commonName, peer_cn, len + 1);
			peer_cn[len] = '\0';
			if (r != len)
			{
				/* shouldn't happen */
				pfree(peer_cn);
				return -1;
			}

			/*
			 * Reject embedded NULLs in certificate common name to prevent
			 * attacks like CVE-2009-4034.
			 */
			if (len != strlen(peer_cn))
			{
				ereport(COMMERROR,
						(errcode(ERRCODE_PROTOCOL_VIOLATION),
						 errmsg("SSL certificate's common name contains embedded null")));
				pfree(peer_cn);
				return -1;
			}

			port->peer_cn = peer_cn;
		}
		port->peer_cert_valid = true;
	}

	ereport(DEBUG2,
			(errmsg("SSL connection from \"%s\"",
					port->peer_cn ? port->peer_cn : "(anonymous)")));

	/* set up debugging/info callback */
	SSL_CTX_set_info_callback(SSL_context, info_cb);

	return 0;
}

/*
 *	Close SSL connection.
 */
void
be_tls_close(Port *port)
{
	if (port->ssl)
	{
		SSL_shutdown(port->ssl);
		SSL_free(port->ssl);
		port->ssl = NULL;
		port->ssl_in_use = false;
	}

	if (port->peer)
	{
		X509_free(port->peer);
		port->peer = NULL;
	}

	if (port->peer_cn)
	{
		pfree(port->peer_cn);
		port->peer_cn = NULL;
	}
}

/*
 *	Read data from a secure connection.
 */
ssize_t
be_tls_read(Port *port, void *ptr, size_t len, int *waitfor)
{
	ssize_t		n;
	int			err;

	errno = 0;
	n = SSL_read(port->ssl, ptr, len);
	err = SSL_get_error(port->ssl, n);
	switch (err)
	{
		case SSL_ERROR_NONE:
			port->count += n;
			break;
		case SSL_ERROR_WANT_READ:
			*waitfor = WL_SOCKET_READABLE;
			errno = EWOULDBLOCK;
			n = -1;
			break;
		case SSL_ERROR_WANT_WRITE:
			*waitfor = WL_SOCKET_WRITEABLE;
			errno = EWOULDBLOCK;
			n = -1;
			break;
		case SSL_ERROR_SYSCALL:
			/* leave it to caller to ereport the value of errno */
			if (n != -1)
			{
				errno = ECONNRESET;
				n = -1;
			}
			break;
		case SSL_ERROR_SSL:
			ereport(COMMERROR,
					(errcode(ERRCODE_PROTOCOL_VIOLATION),
					 errmsg("SSL error: %s", SSLerrmessage())));
			/* fall through */
		case SSL_ERROR_ZERO_RETURN:
			errno = ECONNRESET;
			n = -1;
			break;
		default:
			ereport(COMMERROR,
					(errcode(ERRCODE_PROTOCOL_VIOLATION),
					 errmsg("unrecognized SSL error code: %d",
							err)));
			errno = ECONNRESET;
			n = -1;
			break;
	}

	return n;
}

/*
 *	Write data to a secure connection.
 */
ssize_t
be_tls_write(Port *port, void *ptr, size_t len, int *waitfor)
{
	ssize_t		n;
	int			err;

	errno = 0;
	n = SSL_write(port->ssl, ptr, len);
	err = SSL_get_error(port->ssl, n);
	switch (err)
	{
		case SSL_ERROR_NONE:
			port->count += n;
			break;
		case SSL_ERROR_WANT_READ:
			*waitfor = WL_SOCKET_READABLE;
			errno = EWOULDBLOCK;
			n = -1;
			break;
		case SSL_ERROR_WANT_WRITE:
			*waitfor = WL_SOCKET_WRITEABLE;
			errno = EWOULDBLOCK;
			n = -1;
			break;
		case SSL_ERROR_SYSCALL:
			/* leave it to caller to ereport the value of errno */
			if (n != -1)
			{
				errno = ECONNRESET;
				n = -1;
			}
			break;
		case SSL_ERROR_SSL:
			ereport(COMMERROR,
					(errcode(ERRCODE_PROTOCOL_VIOLATION),
					 errmsg("SSL error: %s", SSLerrmessage())));
			/* fall through */
		case SSL_ERROR_ZERO_RETURN:
			errno = ECONNRESET;
			n = -1;
			break;
		default:
			ereport(COMMERROR,
					(errcode(ERRCODE_PROTOCOL_VIOLATION),
					 errmsg("unrecognized SSL error code: %d",
							err)));
			errno = ECONNRESET;
			n = -1;
			break;
	}

	return n;
}

/* ------------------------------------------------------------ */
/*						Internal functions						*/
/* ------------------------------------------------------------ */

/*
 * Private substitute BIO: this does the sending and receiving using send() and
 * recv() instead. This is so that we can enable and disable interrupts
 * just while calling recv(). We cannot have interrupts occurring while
 * the bulk of openssl runs, because it uses malloc() and possibly other
 * non-reentrant libc facilities. We also need to call send() and recv()
 * directly so it gets passed through the socket/signals layer on Win32.
 *
 * These functions are closely modelled on the standard socket BIO in OpenSSL;
 * see sock_read() and sock_write() in OpenSSL's crypto/bio/bss_sock.c.
 * XXX OpenSSL 1.0.1e considers many more errcodes than just EINTR as reasons
 * to retry; do we need to adopt their logic for that?
 */

static bool my_bio_initialized = false;
static BIO_METHOD my_bio_methods;

static int
my_sock_read(BIO *h, char *buf, int size)
{
	int			res = 0;

	if (buf != NULL)
	{
		res = secure_raw_read(((Port *) h->ptr), buf, size);
		BIO_clear_retry_flags(h);
		if (res <= 0)
		{
			/* If we were interrupted, tell caller to retry */
			if (errno == EINTR || errno == EWOULDBLOCK || errno == EAGAIN)
			{
				BIO_set_retry_read(h);
			}
		}
	}

	return res;
}

static int
my_sock_write(BIO *h, const char *buf, int size)
{
	int			res = 0;

	res = secure_raw_write(((Port *) h->ptr), buf, size);
	BIO_clear_retry_flags(h);
	if (res <= 0)
	{
		/* If we were interrupted, tell caller to retry */
		if (errno == EINTR || errno == EWOULDBLOCK || errno == EAGAIN)
		{
			BIO_set_retry_write(h);
		}
	}

	return res;
}

static BIO_METHOD *
my_BIO_s_socket(void)
{
	if (!my_bio_initialized)
	{
		memcpy(&my_bio_methods, BIO_s_socket(), sizeof(BIO_METHOD));
		my_bio_methods.bread = my_sock_read;
		my_bio_methods.bwrite = my_sock_write;
		my_bio_initialized = true;
	}
	return &my_bio_methods;
}

/* This should exactly match openssl's SSL_set_fd except for using my BIO */
static int
my_SSL_set_fd(Port *port, int fd)
{
	int			ret = 0;
	BIO		   *bio = NULL;

	bio = BIO_new(my_BIO_s_socket());

	if (bio == NULL)
	{
		SSLerr(SSL_F_SSL_SET_FD, ERR_R_BUF_LIB);
		goto err;
	}
	/* Use 'ptr' to store pointer to PGconn */
	bio->ptr = port;

	BIO_set_fd(bio, fd, BIO_NOCLOSE);
	SSL_set_bio(port->ssl, bio, bio);
	ret = 1;
err:
	return ret;
}

/*
 *	Load precomputed DH parameters.
 *
 *	To prevent "downgrade" attacks, we perform a number of checks
 *	to verify that the DBA-generated DH parameters file contains
 *	what we expect it to contain.
 */
static DH  *
load_dh_file(int keylength)
{
	FILE	   *fp;
	char		fnbuf[MAXPGPATH];
	DH		   *dh = NULL;
	int			codes;

	/* attempt to open file.  It's not an error if it doesn't exist. */
	snprintf(fnbuf, sizeof(fnbuf), "dh%d.pem", keylength);
	if ((fp = fopen(fnbuf, "r")) == NULL)
		return NULL;

/*	flock(fileno(fp), LOCK_SH); */
	dh = PEM_read_DHparams(fp, NULL, NULL, NULL);
/*	flock(fileno(fp), LOCK_UN); */
	fclose(fp);

	/* is the prime the correct size? */
	if (dh != NULL && 8 * DH_size(dh) < keylength)
	{
		elog(LOG, "DH errors (%s): %d bits expected, %d bits found",
			 fnbuf, keylength, 8 * DH_size(dh));
		dh = NULL;
	}

	/* make sure the DH parameters are usable */
	if (dh != NULL)
	{
		if (DH_check(dh, &codes) == 0)
		{
			elog(LOG, "DH_check error (%s): %s", fnbuf, SSLerrmessage());
			return NULL;
		}
		if (codes & DH_CHECK_P_NOT_PRIME)
		{
			elog(LOG, "DH error (%s): p is not prime", fnbuf);
			return NULL;
		}
		if ((codes & DH_NOT_SUITABLE_GENERATOR) &&
			(codes & DH_CHECK_P_NOT_SAFE_PRIME))
		{
			elog(LOG,
				 "DH error (%s): neither suitable generator or safe prime",
				 fnbuf);
			return NULL;
		}
	}

	return dh;
}

/*
 *	Load hardcoded DH parameters.
 *
 *	To prevent problems if the DH parameters files don't even
 *	exist, we can load DH parameters hardcoded into this file.
 */
static DH  *
load_dh_buffer(const char *buffer, size_t len)
{
	BIO		   *bio;
	DH		   *dh = NULL;

	bio = BIO_new_mem_buf((char *) buffer, len);
	if (bio == NULL)
		return NULL;
	dh = PEM_read_bio_DHparams(bio, NULL, NULL, NULL);
	if (dh == NULL)
		ereport(DEBUG2,
				(errmsg_internal("DH load buffer: %s",
								 SSLerrmessage())));
	BIO_free(bio);

	return dh;
}

/*
 *	Generate an ephemeral DH key.  Because this can take a long
 *	time to compute, we can use precomputed parameters of the
 *	common key sizes.
 *
 *	Since few sites will bother to precompute these parameter
 *	files, we also provide a fallback to the parameters provided
 *	by the OpenSSL project.
 *
 *	These values can be static (once loaded or computed) since
 *	the OpenSSL library can efficiently generate random keys from
 *	the information provided.
 */
static DH  *
tmp_dh_cb(SSL *s, int is_export, int keylength)
{
	DH		   *r = NULL;
	static DH  *dh = NULL;
	static DH  *dh512 = NULL;
	static DH  *dh1024 = NULL;
	static DH  *dh2048 = NULL;
	static DH  *dh4096 = NULL;

	switch (keylength)
	{
		case 512:
			if (dh512 == NULL)
				dh512 = load_dh_file(keylength);
			if (dh512 == NULL)
				dh512 = load_dh_buffer(file_dh512, sizeof file_dh512);
			r = dh512;
			break;

		case 1024:
			if (dh1024 == NULL)
				dh1024 = load_dh_file(keylength);
			if (dh1024 == NULL)
				dh1024 = load_dh_buffer(file_dh1024, sizeof file_dh1024);
			r = dh1024;
			break;

		case 2048:
			if (dh2048 == NULL)
				dh2048 = load_dh_file(keylength);
			if (dh2048 == NULL)
				dh2048 = load_dh_buffer(file_dh2048, sizeof file_dh2048);
			r = dh2048;
			break;

		case 4096:
			if (dh4096 == NULL)
				dh4096 = load_dh_file(keylength);
			if (dh4096 == NULL)
				dh4096 = load_dh_buffer(file_dh4096, sizeof file_dh4096);
			r = dh4096;
			break;

		default:
			if (dh == NULL)
				dh = load_dh_file(keylength);
			r = dh;
	}

	/* this may take a long time, but it may be necessary... */
	if (r == NULL || 8 * DH_size(r) < keylength)
	{
		ereport(DEBUG2,
				(errmsg_internal("DH: generating parameters (%d bits)",
								 keylength)));
		r = DH_generate_parameters(keylength, DH_GENERATOR_2, NULL, NULL);
	}

	return r;
}

/*
 *	Certificate verification callback
 *
 *	This callback allows us to log intermediate problems during
 *	verification, but for now we'll see if the final error message
 *	contains enough information.
 *
 *	This callback also allows us to override the default acceptance
 *	criteria (e.g., accepting self-signed or expired certs), but
 *	for now we accept the default checks.
 */
static int
verify_cb(int ok, X509_STORE_CTX *ctx)
{
	return ok;
}

/*
 *	This callback is used to copy SSL information messages
 *	into the PostgreSQL log.
 */
static void
info_cb(const SSL *ssl, int type, int args)
{
	switch (type)
	{
		case SSL_CB_HANDSHAKE_START:
			ereport(DEBUG4,
					(errmsg_internal("SSL: handshake start")));
			break;
		case SSL_CB_HANDSHAKE_DONE:
			ereport(DEBUG4,
					(errmsg_internal("SSL: handshake done")));
			break;
		case SSL_CB_ACCEPT_LOOP:
			ereport(DEBUG4,
					(errmsg_internal("SSL: accept loop")));
			break;
		case SSL_CB_ACCEPT_EXIT:
			ereport(DEBUG4,
					(errmsg_internal("SSL: accept exit (%d)", args)));
			break;
		case SSL_CB_CONNECT_LOOP:
			ereport(DEBUG4,
					(errmsg_internal("SSL: connect loop")));
			break;
		case SSL_CB_CONNECT_EXIT:
			ereport(DEBUG4,
					(errmsg_internal("SSL: connect exit (%d)", args)));
			break;
		case SSL_CB_READ_ALERT:
			ereport(DEBUG4,
					(errmsg_internal("SSL: read alert (0x%04x)", args)));
			break;
		case SSL_CB_WRITE_ALERT:
			ereport(DEBUG4,
					(errmsg_internal("SSL: write alert (0x%04x)", args)));
			break;
	}
}

static void
initialize_ecdh(void)
{
#if (OPENSSL_VERSION_NUMBER >= 0x0090800fL) && !defined(OPENSSL_NO_ECDH)
	EC_KEY	   *ecdh;
	int			nid;

	nid = OBJ_sn2nid(SSLECDHCurve);
	if (!nid)
		ereport(FATAL,
				(errmsg("ECDH: unrecognized curve name: %s", SSLECDHCurve)));

	ecdh = EC_KEY_new_by_curve_name(nid);
	if (!ecdh)
		ereport(FATAL,
				(errmsg("ECDH: could not create key")));

	SSL_CTX_set_options(SSL_context, SSL_OP_SINGLE_ECDH_USE);
	SSL_CTX_set_tmp_ecdh(SSL_context, ecdh);
	EC_KEY_free(ecdh);
#endif
}

/*
 * Obtain reason string for last SSL error
 *
 * Some caution is needed here since ERR_reason_error_string will
 * return NULL if it doesn't recognize the error code.  We don't
 * want to return NULL ever.
 */
static const char *
SSLerrmessage(void)
{
	unsigned long errcode;
	const char *errreason;
	static char errbuf[32];

	errcode = ERR_get_error();
	if (errcode == 0)
		return _("no SSL error reported");
	errreason = ERR_reason_error_string(errcode);
	if (errreason != NULL)
		return errreason;
	snprintf(errbuf, sizeof(errbuf), _("SSL error code %lu"), errcode);
	return errbuf;
}

/*
 * Return information about the SSL connection
 */
int
be_tls_get_cipher_bits(Port *port)
{
	int			bits;

	if (port->ssl)
	{
		SSL_get_cipher_bits(port->ssl, &bits);
		return bits;
	}
	else
		return 0;
}

bool
be_tls_get_compression(Port *port)
{
	if (port->ssl)
		return (SSL_get_current_compression(port->ssl) != NULL);
	else
		return false;
}

void
be_tls_get_version(Port *port, char *ptr, size_t len)
{
	if (port->ssl)
		strlcpy(ptr, SSL_get_version(port->ssl), len);
	else
		ptr[0] = '\0';
}

void
be_tls_get_cipher(Port *port, char *ptr, size_t len)
{
	if (port->ssl)
		strlcpy(ptr, SSL_get_cipher(port->ssl), len);
	else
		ptr[0] = '\0';
}

void
be_tls_get_peerdn_name(Port *port, char *ptr, size_t len)
{
	if (port->peer)
		strlcpy(ptr, X509_NAME_to_cstring(X509_get_subject_name(port->peer)), len);
	else
		ptr[0] = '\0';
}

/*
 * Convert an X509 subject name to a cstring.
 *
 */
static char *
X509_NAME_to_cstring(X509_NAME *name)
{
	BIO		   *membuf = BIO_new(BIO_s_mem());
	int			i,
				nid,
				count = X509_NAME_entry_count(name);
	X509_NAME_ENTRY *e;
	ASN1_STRING *v;
	const char *field_name;
	size_t		size;
	char		nullterm;
	char	   *sp;
	char	   *dp;
	char	   *result;

	(void) BIO_set_close(membuf, BIO_CLOSE);
	for (i = 0; i < count; i++)
	{
		e = X509_NAME_get_entry(name, i);
		nid = OBJ_obj2nid(X509_NAME_ENTRY_get_object(e));
		v = X509_NAME_ENTRY_get_data(e);
		field_name = OBJ_nid2sn(nid);
		if (!field_name)
			field_name = OBJ_nid2ln(nid);
		BIO_printf(membuf, "/%s=", field_name);
		ASN1_STRING_print_ex(membuf, v,
							 ((ASN1_STRFLGS_RFC2253 & ~ASN1_STRFLGS_ESC_MSB)
							  | ASN1_STRFLGS_UTF8_CONVERT));
	}

	/* ensure null termination of the BIO's content */
	nullterm = '\0';
	BIO_write(membuf, &nullterm, 1);
	size = BIO_get_mem_data(membuf, &sp);
	dp = pg_any_to_server(sp, size - 1, PG_UTF8);

	result = pstrdup(dp);
	if (dp != sp)
		pfree(dp);
	BIO_free(membuf);

	return result;
}