be-secure-openssl.c

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/*-------------------------------------------------------------------------
 *
 * be-secure-openssl.c
 *    functions for OpenSSL support in the backend.
 *
 *
 * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/libpq/be-secure-openssl.c
 *
 *-------------------------------------------------------------------------
 */

#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>
#include <openssl/conf.h>
#ifndef OPENSSL_NO_ECDH
#include <openssl/ec.h>
#endif

#include "common/openssl.h"
#include "libpq/libpq.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "storage/fd.h"
#include "storage/latch.h"
#include "tcop/tcopprot.h"
#include "utils/memutils.h"

/* default init hook can be overridden by a shared library */
static void default_openssl_tls_init(SSL_CTX *context, bool isServerStart);
openssl_tls_init_hook_typ openssl_tls_init_hook = default_openssl_tls_init;

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(char *filename, bool isServerStart);
static DH  *load_dh_buffer(const char *, size_t);
static int  ssl_external_passwd_cb(char *buf, int size, int rwflag, void *userdata);
static int  dummy_ssl_passwd_cb(char *buf, int size, int rwflag, void *userdata);
static int  verify_cb(int, X509_STORE_CTX *);
static void info_cb(const SSL *ssl, int type, int args);
static bool initialize_dh(SSL_CTX *context, bool isServerStart);
static bool initialize_ecdh(SSL_CTX *context, bool isServerStart);
static const char *SSLerrmessage(unsigned long ecode);

static char *X509_NAME_to_cstring(X509_NAME *name);

static SSL_CTX *SSL_context = NULL;
static bool SSL_initialized = false;
static bool dummy_ssl_passwd_cb_called = false;
static bool ssl_is_server_start;

static int  ssl_protocol_version_to_openssl(int v);
static const char *ssl_protocol_version_to_string(int v);

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

int
be_tls_init(bool isServerStart)
{
    STACK_OF(X509_NAME) * root_cert_list = NULL;
    SSL_CTX    *context;
    int         ssl_ver_min = -1;
    int         ssl_ver_max = -1;

    /* This stuff need be done only once. */
    if (!SSL_initialized)
    {
#ifdef HAVE_OPENSSL_INIT_SSL
        OPENSSL_init_ssl(OPENSSL_INIT_LOAD_CONFIG, NULL);
#else
        OPENSSL_config(NULL);
        SSL_library_init();
        SSL_load_error_strings();
#endif
        SSL_initialized = true;
    }

    /*
     * 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).
     */
    context = SSL_CTX_new(SSLv23_method());
    if (!context)
    {
        ereport(isServerStart ? FATAL : LOG,
                (errmsg("could not create SSL context: %s",
                        SSLerrmessage(ERR_get_error()))));
        goto error;
    }

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

    /*
     * Call init hook (usually to set password callback)
     */
    (*openssl_tls_init_hook) (context, isServerStart);

    /* used by the callback */
    ssl_is_server_start = isServerStart;

    /*
     * Load and verify server's certificate and private key
     */
    if (SSL_CTX_use_certificate_chain_file(context, ssl_cert_file) != 1)
    {
        ereport(isServerStart ? FATAL : LOG,
                (errcode(ERRCODE_CONFIG_FILE_ERROR),
                 errmsg("could not load server certificate file \"%s\": %s",
                        ssl_cert_file, SSLerrmessage(ERR_get_error()))));
        goto error;
    }

    if (!check_ssl_key_file_permissions(ssl_key_file, isServerStart))
        goto error;

    /*
     * OK, try to load the private key file.
     */
    dummy_ssl_passwd_cb_called = false;

    if (SSL_CTX_use_PrivateKey_file(context,
                                    ssl_key_file,
                                    SSL_FILETYPE_PEM) != 1)
    {
        if (dummy_ssl_passwd_cb_called)
            ereport(isServerStart ? FATAL : LOG,
                    (errcode(ERRCODE_CONFIG_FILE_ERROR),
                     errmsg("private key file \"%s\" cannot be reloaded because it requires a passphrase",
                            ssl_key_file)));
        else
            ereport(isServerStart ? FATAL : LOG,
                    (errcode(ERRCODE_CONFIG_FILE_ERROR),
                     errmsg("could not load private key file \"%s\": %s",
                            ssl_key_file, SSLerrmessage(ERR_get_error()))));
        goto error;
    }

    if (SSL_CTX_check_private_key(context) != 1)
    {
        ereport(isServerStart ? FATAL : LOG,
                (errcode(ERRCODE_CONFIG_FILE_ERROR),
                 errmsg("check of private key failed: %s",
                        SSLerrmessage(ERR_get_error()))));
        goto error;
    }

    if (ssl_min_protocol_version)
    {
        ssl_ver_min = ssl_protocol_version_to_openssl(ssl_min_protocol_version);

        if (ssl_ver_min == -1)
        {
            ereport(isServerStart ? FATAL : LOG,
            /*- translator: first %s is a GUC option name, second %s is its value */
                    (errmsg("\"%s\" setting \"%s\" not supported by this build",
                            "ssl_min_protocol_version",
                            GetConfigOption("ssl_min_protocol_version",
                                            false, false))));
            goto error;
        }

        if (!SSL_CTX_set_min_proto_version(context, ssl_ver_min))
        {
            ereport(isServerStart ? FATAL : LOG,
                    (errmsg("could not set minimum SSL protocol version")));
            goto error;
        }
    }

    if (ssl_max_protocol_version)
    {
        ssl_ver_max = ssl_protocol_version_to_openssl(ssl_max_protocol_version);

        if (ssl_ver_max == -1)
        {
            ereport(isServerStart ? FATAL : LOG,
            /*- translator: first %s is a GUC option name, second %s is its value */
                    (errmsg("\"%s\" setting \"%s\" not supported by this build",
                            "ssl_max_protocol_version",
                            GetConfigOption("ssl_max_protocol_version",
                                            false, false))));
            goto error;
        }

        if (!SSL_CTX_set_max_proto_version(context, ssl_ver_max))
        {
            ereport(isServerStart ? FATAL : LOG,
                    (errmsg("could not set maximum SSL protocol version")));
            goto error;
        }
    }

    /* Check compatibility of min/max protocols */
    if (ssl_min_protocol_version &&
        ssl_max_protocol_version)
    {
        /*
         * No need to check for invalid values (-1) for each protocol number
         * as the code above would have already generated an error.
         */
        if (ssl_ver_min > ssl_ver_max)
        {
            ereport(isServerStart ? FATAL : LOG,
                    (errmsg("could not set SSL protocol version range"),
                     errdetail("\"%s\" cannot be higher than \"%s\"",
                               "ssl_min_protocol_version",
                               "ssl_max_protocol_version")));
            goto error;
        }
    }

    /* disallow SSL session tickets */
    SSL_CTX_set_options(context, SSL_OP_NO_TICKET);

    /* disallow SSL session caching, too */
    SSL_CTX_set_session_cache_mode(context, SSL_SESS_CACHE_OFF);

    /* set up ephemeral DH and ECDH keys */
    if (!initialize_dh(context, isServerStart))
        goto error;
    if (!initialize_ecdh(context, isServerStart))
        goto error;

    /* set up the allowed cipher list */
    if (SSL_CTX_set_cipher_list(context, SSLCipherSuites) != 1)
    {
        ereport(isServerStart ? FATAL : LOG,
                (errcode(ERRCODE_CONFIG_FILE_ERROR),
                 errmsg("could not set the cipher list (no valid ciphers available)")));
        goto error;
    }

    /* Let server choose order */
    if (SSLPreferServerCiphers)
        SSL_CTX_set_options(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(context, ssl_ca_file, NULL) != 1 ||
            (root_cert_list = SSL_load_client_CA_file(ssl_ca_file)) == NULL)
        {
            ereport(isServerStart ? FATAL : LOG,
                    (errcode(ERRCODE_CONFIG_FILE_ERROR),
                     errmsg("could not load root certificate file \"%s\": %s",
                            ssl_ca_file, SSLerrmessage(ERR_get_error()))));
            goto error;
        }
    }

    /*----------
     * 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(context);

        if (cvstore)
        {
            /* Set the flags to check against the complete CRL chain */
            if (X509_STORE_load_locations(cvstore, ssl_crl_file, NULL) == 1)
            {
                X509_STORE_set_flags(cvstore,
                                     X509_V_FLAG_CRL_CHECK | X509_V_FLAG_CRL_CHECK_ALL);
            }
            else
            {
                ereport(isServerStart ? FATAL : LOG,
                        (errcode(ERRCODE_CONFIG_FILE_ERROR),
                         errmsg("could not load SSL certificate revocation list file \"%s\": %s",
                                ssl_crl_file, SSLerrmessage(ERR_get_error()))));
                goto error;
            }
        }
    }

    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(context,
                           (SSL_VERIFY_PEER |
                            SSL_VERIFY_CLIENT_ONCE),
                           verify_cb);

        /*
         * 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(context, root_cert_list);
    }

    /*
     * Success!  Replace any existing SSL_context.
     */
    if (SSL_context)
        SSL_CTX_free(SSL_context);

    SSL_context = context;

    /*
     * Set flag to remember whether CA store has been loaded into SSL_context.
     */
    if (ssl_ca_file[0])
        ssl_loaded_verify_locations = true;
    else
        ssl_loaded_verify_locations = false;

    return 0;

error:
    if (context)
        SSL_CTX_free(context);
    return -1;
}

void
be_tls_destroy(void)
{
    if (SSL_context)
        SSL_CTX_free(SSL_context);
    SSL_context = NULL;
    ssl_loaded_verify_locations = false;
}

int
be_tls_open_server(Port *port)
{
    int         r;
    int         err;
    int         waitfor;
    unsigned long ecode;
    bool        give_proto_hint;

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

    if (!SSL_context)
    {
        ereport(COMMERROR,
                (errcode(ERRCODE_PROTOCOL_VIOLATION),
                 errmsg("could not initialize SSL connection: SSL context not set up")));
        return -1;
    }

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

aloop:

    /*
     * Prepare to call SSL_get_error() by clearing thread's OpenSSL error
     * queue.  In general, the current thread's error queue must be empty
     * before the TLS/SSL I/O operation is attempted, or SSL_get_error() will
     * not work reliably.  An extension may have failed to clear the
     * per-thread error queue following another call to an OpenSSL I/O
     * routine.
     */
    ERR_clear_error();
    r = SSL_accept(port->ssl);
    if (r <= 0)
    {
        err = SSL_get_error(port->ssl, r);

        /*
         * Other clients of OpenSSL in the backend may fail to call
         * ERR_get_error(), but we always do, so as to not cause problems for
         * OpenSSL clients that don't call ERR_clear_error() defensively.  Be
         * sure that this happens by calling now. SSL_get_error() relies on
         * the OpenSSL per-thread error queue being intact, so this is the
         * earliest possible point ERR_get_error() may be called.
         */
        ecode = ERR_get_error();
        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 | WL_EXIT_ON_PM_DEATH;
                else
                    waitfor = WL_SOCKET_WRITEABLE | WL_EXIT_ON_PM_DEATH;

                (void) WaitLatchOrSocket(MyLatch, waitfor, port->sock, 0,
                                         WAIT_EVENT_SSL_OPEN_SERVER);
                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:
                switch (ERR_GET_REASON(ecode))
                {
                        /*
                         * UNSUPPORTED_PROTOCOL, WRONG_VERSION_NUMBER, and
                         * TLSV1_ALERT_PROTOCOL_VERSION have been observed
                         * when trying to communicate with an old OpenSSL
                         * library, or when the client and server specify
                         * disjoint protocol ranges.  NO_PROTOCOLS_AVAILABLE
                         * occurs if there's a local misconfiguration (which
                         * can happen despite our checks, if openssl.cnf
                         * injects a limit we didn't account for).  It's not
                         * very clear what would make OpenSSL return the other
                         * codes listed here, but a hint about protocol
                         * versions seems like it's appropriate for all.
                         */
                    case SSL_R_NO_PROTOCOLS_AVAILABLE:
                    case SSL_R_UNSUPPORTED_PROTOCOL:
                    case SSL_R_BAD_PROTOCOL_VERSION_NUMBER:
                    case SSL_R_UNKNOWN_PROTOCOL:
                    case SSL_R_UNKNOWN_SSL_VERSION:
                    case SSL_R_UNSUPPORTED_SSL_VERSION:
                    case SSL_R_WRONG_SSL_VERSION:
                    case SSL_R_WRONG_VERSION_NUMBER:
                    case SSL_R_TLSV1_ALERT_PROTOCOL_VERSION:
#ifdef SSL_R_VERSION_TOO_HIGH
                    case SSL_R_VERSION_TOO_HIGH:
                    case SSL_R_VERSION_TOO_LOW:
#endif
                        give_proto_hint = true;
                        break;
                    default:
                        give_proto_hint = false;
                        break;
                }
                ereport(COMMERROR,
                        (errcode(ERRCODE_PROTOCOL_VIOLATION),
                         errmsg("could not accept SSL connection: %s",
                                SSLerrmessage(ecode)),
                         give_proto_hint ?
                         errhint("This may indicate that the client does not support any SSL protocol version between %s and %s.",
                                 ssl_min_protocol_version ?
                                 ssl_protocol_version_to_string(ssl_min_protocol_version) :
                                 MIN_OPENSSL_TLS_VERSION,
                                 ssl_max_protocol_version ?
                                 ssl_protocol_version_to_string(ssl_max_protocol_version) :
                                 MAX_OPENSSL_TLS_VERSION) : 0));
                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;
    }

    /* 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;
    }

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

    return 0;
}

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;
    }
}

ssize_t
be_tls_read(Port *port, void *ptr, size_t len, int *waitfor)
{
    ssize_t     n;
    int         err;
    unsigned long ecode;

    errno = 0;
    ERR_clear_error();
    n = SSL_read(port->ssl, ptr, len);
    err = SSL_get_error(port->ssl, n);
    ecode = (err != SSL_ERROR_NONE || n < 0) ? ERR_get_error() : 0;
    switch (err)
    {
        case SSL_ERROR_NONE:
            /* a-ok */
            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(ecode))));
            errno = ECONNRESET;
            n = -1;
            break;
        case SSL_ERROR_ZERO_RETURN:
            /* connection was cleanly shut down by peer */
            n = 0;
            break;
        default:
            ereport(COMMERROR,
                    (errcode(ERRCODE_PROTOCOL_VIOLATION),
                     errmsg("unrecognized SSL error code: %d",
                            err)));
            errno = ECONNRESET;
            n = -1;
            break;
    }

    return n;
}

ssize_t
be_tls_write(Port *port, void *ptr, size_t len, int *waitfor)
{
    ssize_t     n;
    int         err;
    unsigned long ecode;

    errno = 0;
    ERR_clear_error();
    n = SSL_write(port->ssl, ptr, len);
    err = SSL_get_error(port->ssl, n);
    ecode = (err != SSL_ERROR_NONE || n < 0) ? ERR_get_error() : 0;
    switch (err)
    {
        case SSL_ERROR_NONE:
            /* a-ok */
            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(ecode))));
            errno = ECONNRESET;
            n = -1;
            break;
        case SSL_ERROR_ZERO_RETURN:

            /*
             * the SSL connection was closed, leave it to the caller to
             * ereport it
             */
            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?
 */

#ifndef HAVE_BIO_GET_DATA
#define BIO_get_data(bio) (bio->ptr)
#define BIO_set_data(bio, data) (bio->ptr = data)
#endif

static BIO_METHOD *my_bio_methods = NULL;

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

    if (buf != NULL)
    {
        res = secure_raw_read(((Port *) BIO_get_data(h)), 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 *) BIO_get_data(h)), 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_methods)
    {
        BIO_METHOD *biom = (BIO_METHOD *) BIO_s_socket();
#ifdef HAVE_BIO_METH_NEW
        int         my_bio_index;

        my_bio_index = BIO_get_new_index();
        if (my_bio_index == -1)
            return NULL;
        my_bio_methods = BIO_meth_new(my_bio_index, "PostgreSQL backend socket");
        if (!my_bio_methods)
            return NULL;
        if (!BIO_meth_set_write(my_bio_methods, my_sock_write) ||
            !BIO_meth_set_read(my_bio_methods, my_sock_read) ||
            !BIO_meth_set_gets(my_bio_methods, BIO_meth_get_gets(biom)) ||
            !BIO_meth_set_puts(my_bio_methods, BIO_meth_get_puts(biom)) ||
            !BIO_meth_set_ctrl(my_bio_methods, BIO_meth_get_ctrl(biom)) ||
            !BIO_meth_set_create(my_bio_methods, BIO_meth_get_create(biom)) ||
            !BIO_meth_set_destroy(my_bio_methods, BIO_meth_get_destroy(biom)) ||
            !BIO_meth_set_callback_ctrl(my_bio_methods, BIO_meth_get_callback_ctrl(biom)))
        {
            BIO_meth_free(my_bio_methods);
            my_bio_methods = NULL;
            return NULL;
        }
#else
        my_bio_methods = malloc(sizeof(BIO_METHOD));
        if (!my_bio_methods)
            return NULL;
        memcpy(my_bio_methods, biom, sizeof(BIO_METHOD));
        my_bio_methods->bread = my_sock_read;
        my_bio_methods->bwrite = my_sock_write;
#endif
    }
    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;
    BIO_METHOD *bio_method;

    bio_method = my_BIO_s_socket();
    if (bio_method == NULL)
    {
        SSLerr(SSL_F_SSL_SET_FD, ERR_R_BUF_LIB);
        goto err;
    }
    bio = BIO_new(bio_method);

    if (bio == NULL)
    {
        SSLerr(SSL_F_SSL_SET_FD, ERR_R_BUF_LIB);
        goto err;
    }
    BIO_set_data(bio, 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(char *filename, bool isServerStart)
{
    FILE       *fp;
    DH         *dh = NULL;
    int         codes;

    /* attempt to open file.  It's not an error if it doesn't exist. */
    if ((fp = AllocateFile(filename, "r")) == NULL)
    {
        ereport(isServerStart ? FATAL : LOG,
                (errcode_for_file_access(),
                 errmsg("could not open DH parameters file \"%s\": %m",
                        filename)));
        return NULL;
    }

    dh = PEM_read_DHparams(fp, NULL, NULL, NULL);
    FreeFile(fp);

    if (dh == NULL)
    {
        ereport(isServerStart ? FATAL : LOG,
                (errcode(ERRCODE_CONFIG_FILE_ERROR),
                 errmsg("could not load DH parameters file: %s",
                        SSLerrmessage(ERR_get_error()))));
        return NULL;
    }

    /* make sure the DH parameters are usable */
    if (DH_check(dh, &codes) == 0)
    {
        ereport(isServerStart ? FATAL : LOG,
                (errcode(ERRCODE_CONFIG_FILE_ERROR),
                 errmsg("invalid DH parameters: %s",
                        SSLerrmessage(ERR_get_error()))));
        return NULL;
    }
    if (codes & DH_CHECK_P_NOT_PRIME)
    {
        ereport(isServerStart ? FATAL : LOG,
                (errcode(ERRCODE_CONFIG_FILE_ERROR),
                 errmsg("invalid DH parameters: p is not prime")));
        return NULL;
    }
    if ((codes & DH_NOT_SUITABLE_GENERATOR) &&
        (codes & DH_CHECK_P_NOT_SAFE_PRIME))
    {
        ereport(isServerStart ? FATAL : LOG,
                (errcode(ERRCODE_CONFIG_FILE_ERROR),
                 errmsg("invalid DH parameters: neither suitable generator or safe prime")));
        return NULL;
    }

    return dh;
}

/*
 *  Load hardcoded DH parameters.
 *
 *  If DH parameters cannot be loaded from a specified file, we can load
 *  the hardcoded DH parameters supplied with the backend to prevent
 *  problems.
 */
static DH  *
load_dh_buffer(const char *buffer, size_t len)
{
    BIO        *bio;
    DH         *dh = NULL;

    bio = BIO_new_mem_buf(unconstify(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(ERR_get_error()))));
    BIO_free(bio);

    return dh;
}

/*
 *  Passphrase collection callback using ssl_passphrase_command
 */
static int
ssl_external_passwd_cb(char *buf, int size, int rwflag, void *userdata)
{
    /* same prompt as OpenSSL uses internally */
    const char *prompt = "Enter PEM pass phrase:";

    Assert(rwflag == 0);

    return run_ssl_passphrase_command(prompt, ssl_is_server_start, buf, size);
}

/*
 * Dummy passphrase callback
 *
 * If OpenSSL is told to use a passphrase-protected server key, by default
 * it will issue a prompt on /dev/tty and try to read a key from there.
 * That's no good during a postmaster SIGHUP cycle, not to mention SSL context
 * reload in an EXEC_BACKEND postmaster child.  So override it with this dummy
 * function that just returns an empty passphrase, guaranteeing failure.
 */
static int
dummy_ssl_passwd_cb(char *buf, int size, int rwflag, void *userdata)
{
    /* Set flag to change the error message we'll report */
    dummy_ssl_passwd_cb_called = true;
    /* And return empty string */
    Assert(size > 0);
    buf[0] = '\0';
    return 0;
}

/*
 *  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;
    }
}

/*
 * Set DH parameters for generating ephemeral DH keys.  The
 * DH parameters can take a long time to compute, so they must be
 * precomputed.
 *
 * Since few sites will bother to create a parameter file, 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 bool
initialize_dh(SSL_CTX *context, bool isServerStart)
{
    DH         *dh = NULL;

    SSL_CTX_set_options(context, SSL_OP_SINGLE_DH_USE);

    if (ssl_dh_params_file[0])
        dh = load_dh_file(ssl_dh_params_file, isServerStart);
    if (!dh)
        dh = load_dh_buffer(FILE_DH2048, sizeof(FILE_DH2048));
    if (!dh)
    {
        ereport(isServerStart ? FATAL : LOG,
                (errcode(ERRCODE_CONFIG_FILE_ERROR),
                 errmsg("DH: could not load DH parameters")));
        return false;
    }

    if (SSL_CTX_set_tmp_dh(context, dh) != 1)
    {
        ereport(isServerStart ? FATAL : LOG,
                (errcode(ERRCODE_CONFIG_FILE_ERROR),
                 errmsg("DH: could not set DH parameters: %s",
                        SSLerrmessage(ERR_get_error()))));
        DH_free(dh);
        return false;
    }

    DH_free(dh);
    return true;
}

/*
 * Set ECDH parameters for generating ephemeral Elliptic Curve DH
 * keys.  This is much simpler than the DH parameters, as we just
 * need to provide the name of the curve to OpenSSL.
 */
static bool
initialize_ecdh(SSL_CTX *context, bool isServerStart)
{
#ifndef OPENSSL_NO_ECDH
    EC_KEY     *ecdh;
    int         nid;

    nid = OBJ_sn2nid(SSLECDHCurve);
    if (!nid)
    {
        ereport(isServerStart ? FATAL : LOG,
                (errcode(ERRCODE_CONFIG_FILE_ERROR),
                 errmsg("ECDH: unrecognized curve name: %s", SSLECDHCurve)));
        return false;
    }

    ecdh = EC_KEY_new_by_curve_name(nid);
    if (!ecdh)
    {
        ereport(isServerStart ? FATAL : LOG,
                (errcode(ERRCODE_CONFIG_FILE_ERROR),
                 errmsg("ECDH: could not create key")));
        return false;
    }

    SSL_CTX_set_options(context, SSL_OP_SINGLE_ECDH_USE);
    SSL_CTX_set_tmp_ecdh(context, ecdh);
    EC_KEY_free(ecdh);
#endif

    return true;
}

/*
 * Obtain reason string for passed SSL errcode
 *
 * ERR_get_error() is used by caller to get errcode to pass here.
 *
 * 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(unsigned long ecode)
{
    const char *errreason;
    static char errbuf[36];

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

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;
}

const char *
be_tls_get_version(Port *port)
{
    if (port->ssl)
        return SSL_get_version(port->ssl);
    else
        return NULL;
}

const char *
be_tls_get_cipher(Port *port)
{
    if (port->ssl)
        return SSL_get_cipher(port->ssl);
    else
        return NULL;
}

void
be_tls_get_peer_subject_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';
}

void
be_tls_get_peer_issuer_name(Port *port, char *ptr, size_t len)
{
    if (port->peer)
        strlcpy(ptr, X509_NAME_to_cstring(X509_get_issuer_name(port->peer)), len);
    else
        ptr[0] = '\0';
}

void
be_tls_get_peer_serial(Port *port, char *ptr, size_t len)
{
    if (port->peer)
    {
        ASN1_INTEGER *serial;
        BIGNUM     *b;
        char       *decimal;

        serial = X509_get_serialNumber(port->peer);
        b = ASN1_INTEGER_to_BN(serial, NULL);
        decimal = BN_bn2dec(b);

        BN_free(b);
        strlcpy(ptr, decimal, len);
        OPENSSL_free(decimal);
    }
    else
        ptr[0] = '\0';
}

#ifdef HAVE_X509_GET_SIGNATURE_NID
char *
be_tls_get_certificate_hash(Port *port, size_t *len)
{
    X509       *server_cert;
    char       *cert_hash;
    const EVP_MD *algo_type = NULL;
    unsigned char hash[EVP_MAX_MD_SIZE];    /* size for SHA-512 */
    unsigned int hash_size;
    int         algo_nid;

    *len = 0;
    server_cert = SSL_get_certificate(port->ssl);
    if (server_cert == NULL)
        return NULL;

    /*
     * Get the signature algorithm of the certificate to determine the hash
     * algorithm to use for the result.
     */
    if (!OBJ_find_sigid_algs(X509_get_signature_nid(server_cert),
                             &algo_nid, NULL))
        elog(ERROR, "could not determine server certificate signature algorithm");

    /*
     * The TLS server's certificate bytes need to be hashed with SHA-256 if
     * its signature algorithm is MD5 or SHA-1 as per RFC 5929
     * (https://tools.ietf.org/html/rfc5929#section-4.1).  If something else
     * is used, the same hash as the signature algorithm is used.
     */
    switch (algo_nid)
    {
        case NID_md5:
        case NID_sha1:
            algo_type = EVP_sha256();
            break;
        default:
            algo_type = EVP_get_digestbynid(algo_nid);
            if (algo_type == NULL)
                elog(ERROR, "could not find digest for NID %s",
                     OBJ_nid2sn(algo_nid));
            break;
    }

    /* generate and save the certificate hash */
    if (!X509_digest(server_cert, algo_type, hash, &hash_size))
        elog(ERROR, "could not generate server certificate hash");

    cert_hash = palloc(hash_size);
    memcpy(cert_hash, hash, hash_size);
    *len = hash_size;

    return cert_hash;
}
#endif

/*
 * 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;

    if (membuf == NULL)
        ereport(ERROR,
                (errcode(ERRCODE_OUT_OF_MEMORY),
                 errmsg("failed to create BIO")));

    (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));
        if (nid == NID_undef)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("could not get NID for ASN1_OBJECT object")));
        v = X509_NAME_ENTRY_get_data(e);
        field_name = OBJ_nid2sn(nid);
        if (field_name == NULL)
            field_name = OBJ_nid2ln(nid);
        if (field_name == NULL)
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_PARAMETER_VALUE),
                     errmsg("could not convert NID %d to an ASN1_OBJECT structure", 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);
    if (BIO_free(membuf) != 1)
        elog(ERROR, "could not free OpenSSL BIO structure");

    return result;
}

/*
 * Convert TLS protocol version GUC enum to OpenSSL values
 *
 * This is a straightforward one-to-one mapping, but doing it this way makes
 * guc.c independent of OpenSSL availability and version.
 *
 * If a version is passed that is not supported by the current OpenSSL
 * version, then we return -1.  If a nonnegative value is returned,
 * subsequent code can assume it's working with a supported version.
 *
 * Note: this is rather similar to libpq's routine in fe-secure-openssl.c,
 * so make sure to update both routines if changing this one.
 */
static int
ssl_protocol_version_to_openssl(int v)
{
    switch (v)
    {
        case PG_TLS_ANY:
            return 0;
        case PG_TLS1_VERSION:
            return TLS1_VERSION;
        case PG_TLS1_1_VERSION:
#ifdef TLS1_1_VERSION
            return TLS1_1_VERSION;
#else
            break;
#endif
        case PG_TLS1_2_VERSION:
#ifdef TLS1_2_VERSION
            return TLS1_2_VERSION;
#else
            break;
#endif
        case PG_TLS1_3_VERSION:
#ifdef TLS1_3_VERSION
            return TLS1_3_VERSION;
#else
            break;
#endif
    }

    return -1;
}

/*
 * Likewise provide a mapping to strings.
 */
static const char *
ssl_protocol_version_to_string(int v)
{
    switch (v)
    {
        case PG_TLS_ANY:
            return "any";
        case PG_TLS1_VERSION:
            return "TLSv1";
        case PG_TLS1_1_VERSION:
            return "TLSv1.1";
        case PG_TLS1_2_VERSION:
            return "TLSv1.2";
        case PG_TLS1_3_VERSION:
            return "TLSv1.3";
    }

    return "(unrecognized)";
}


static void
default_openssl_tls_init(SSL_CTX *context, bool isServerStart)
{
    if (isServerStart)
    {
        if (ssl_passphrase_command[0])
            SSL_CTX_set_default_passwd_cb(context, ssl_external_passwd_cb);
    }
    else
    {
        if (ssl_passphrase_command[0] && ssl_passphrase_command_supports_reload)
            SSL_CTX_set_default_passwd_cb(context, ssl_external_passwd_cb);
        else

            /*
             * If reloading and no external command is configured, override
             * OpenSSL's default handling of passphrase-protected files,
             * because we don't want to prompt for a passphrase in an
             * already-running server.
             */
            SSL_CTX_set_default_passwd_cb(context, dummy_ssl_passwd_cb);
    }
}