easy-tls.c

/* -*- Mode: C; c-file-style: "bsd" -*- */
/*
 * easy-tls.c -- generic TLS proxy.
 * $Id: easy-tls.c,v 1.4 2002/03/05 09:07:16 bodo Exp $
 */
/*
 (c) Copyright 1999 Bodo Moeller.  All rights reserved.

 This is free software; you can redistributed and/or modify it
 unter the terms of either
   -  the GNU General Public License as published by the
      Free Software Foundation, version 1, or (at your option)
      any later version,
 or
   -  the following license:
*/
/*
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that each of the following
 * conditions is met:
 *
 * 1. Redistributions qualify as "freeware" or "Open Source Software" under
 *    one of the following terms:
 * 
 *    (a) Redistributions are made at no charge beyond the reasonable cost of
 *        materials and delivery.
 * 
 *    (b) Redistributions are accompanied by a copy of the Source Code
 *        or by an irrevocable offer to provide a copy of the Source Code
 *        for up to three years at the cost of materials and delivery.
 *        Such redistributions must allow further use, modification, and
 *        redistribution of the Source Code under substantially the same
 *        terms as this license.
 *
 * 2. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer. 
 *
 * 3. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 4. All advertising materials mentioning features or use of this
 *    software must display the following acknowledgment:
 *    "This product includes software developed by Bodo Moeller."
 *    (If available, substitute umlauted o for oe.)
 *
 * 5. Redistributions of any form whatsoever must retain the following
 *    acknowledgment:
 *    "This product includes software developed by Bodo Moeller."
 *
 * THIS SOFTWARE IS PROVIDED BY BODO MOELLER ``AS IS'' AND ANY
 * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL BODO MOELLER OR
 * HIS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 */
/*
 * Attribution for OpenSSL library:
 *
 * This product includes cryptographic software written by Eric Young
 * (eay@cryptsoft.com).  This product includes software written by Tim
 * Hudson (tjh@cryptsoft.com).
 * This product includes software developed by the OpenSSL Project
 * for use in the OpenSSL Toolkit. (http://www.openssl.org/)
 */

static char const rcsid[] =
"$Id: easy-tls.c,v 1.4 2002/03/05 09:07:16 bodo Exp $";

#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <stdarg.h>
#include <stdio.h>
#include <string.h>
#include <sys/select.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/utsname.h>
#include <unistd.h>

#include <openssl/crypto.h>
#include <openssl/dh.h>
#include <openssl/dsa.h>
#include <openssl/err.h>
#include <openssl/evp.h>
#include <openssl/opensslv.h>
#include <openssl/pem.h>
#include <openssl/rand.h>
#ifndef NO_RSA
 #include <openssl/rsa.h>
#endif
#include <openssl/ssl.h>
#include <openssl/x509.h>
#include <openssl/x509_vfy.h>

#if OPENSSL_VERSION_NUMBER < 0x00904000L /* 0.9.4-dev */
# error "This program needs OpenSSL 0.9.4 or later."
#endif

#include "easy-tls.h" /* include after <openssl/ssl.h> if both are needed */

#if TLS_INFO_SIZE > PIPE_BUF
# if PIPE_BUF < 512
#  error "PIPE_BUF < 512" /* non-POSIX */
# endif
# error "TLS_INFO_SIZE > PIPE_BUF"
#endif

/*****************************************************************************/

#ifdef TLS_APP
# include TLS_APP
#endif

/* Applications can define:
 *   TLS_APP_PROCESS_INIT -- void ...(int fd, int client_p, void *apparg)
 *   TLS_CUMULATE_ERRORS 
 *   TLS_ERROR_BUFSIZ
 *   TLS_APP_ERRFLUSH -- void ...(int child_p, char *, size_t, void *apparg)
 */

#ifndef TLS_APP_PROCESS_INIT
# define TLS_APP_PROCESS_INIT(fd, client_p, apparg) ((void) 0)
#endif

#ifndef TLS_ERROR_BUFSIZ
# define TLS_ERROR_BUFSIZ (10*160)
#endif
#if TLS_ERROR_BUFSIZ < 2 /* {'\n',0} */
# error "TLS_ERROR_BUFSIZE is too small."
#endif

#ifndef TLS_APP_ERRFLUSH
# define TLS_APP_ERRFLUSH tls_app_errflush
static void
tls_app_errflush(int child_p, char *errbuf, size_t num, void *apparg)
{
    fputs(errbuf, stderr);
}
#endif

/*****************************************************************************/

#ifdef DEBUG_TLS
# define DEBUG_MSG(x) fprintf(stderr,"  %s\n",x)
# define DEBUG_MSG2(x,y) fprintf(stderr, "  %s: %d\n",x,y)
static int tls_loop_count = 0;
static int tls_select_count = 0;
#else
# define DEBUG_MSG(x) (void)0
# define DEBUG_MSG2(x,y) (void)0
#endif

static void tls_rand_seed_uniquely(void);
static void tls_proxy(int clear_fd, int tls_fd, int info_fd, SSL_CTX *ctx, int client_p);
static int tls_socket_nonblocking(int fd);

static int tls_child_p = 0;
static void *tls_child_apparg;


struct tls_start_proxy_args
tls_start_proxy_defaultargs(void)
{
    struct tls_start_proxy_args ret;

    ret.fd = -1;
    ret.client_p = -1;
    ret.ctx = NULL;
    ret.pid = NULL;
    ret.infofd = NULL;
    
    return ret;
}

/* Slice in TLS proxy process at fd.
 * Return value:
 *   0    ok  (*pid is set to child's PID if pid != NULL),
 *   < 0  look at errno
 *   > 0  other error
 *   (return value encodes place of error)
 *
 */
int
tls_start_proxy(struct tls_start_proxy_args a, void *apparg)
{
    int fds[2] = {-1, -1};
    int infofds[2] = {-1, -1};
    int r, getfd, getfl;
    int ret;

    DEBUG_MSG2("tls_start_proxy fd", a.fd);
    DEBUG_MSG2("tls_start_proxy client_p", a.client_p);

    if (a.fd == -1 || a.client_p == -1 || a.ctx == NULL)
	return 1;

    if (a.pid != NULL) {
	*a.pid = 0;
    }
    if (a.infofd != NULL) {
	*a.infofd = -1;
    }

    r = socketpair(AF_UNIX, SOCK_STREAM, 0, fds);
    if (r == -1)
	return -1;
    if (a.fd >= FD_SETSIZE || fds[0] >= FD_SETSIZE) {
	ret = 2;
	goto err;
    }
    if (a.infofd != NULL) {
	r = pipe(infofds);
	if (r == -1) {
	    ret = -3;
	    goto err;
	}
    }

    r = fork();
    if (r == -1) {
	ret = -4;
	goto err;
    }
    if (r == 0) {
	DEBUG_MSG("fork");
	tls_child_p = 1;
	tls_child_apparg = apparg;
	close(fds[1]);
	if (infofds[0] != -1)
	    close(infofds[0]);
	TLS_APP_PROCESS_INIT(a.fd, a.client_p, apparg);
	DEBUG_MSG("TLS_APP_PROCESS_INIT");
	tls_proxy(fds[0], a.fd, infofds[1], a.ctx, a.client_p);
	exit(0);
    }
    if (a.pid != NULL)
	*a.pid = r;
    if (infofds[1] != -1) {
	close(infofds[1]);
	infofds[1] = -1;
    }
    /* install fds[1] in place of fd: */
    close(fds[0]);
    fds[0] = -1;
    getfd = fcntl(a.fd, F_GETFD);
    getfl = fcntl(a.fd, F_GETFL);
    r = dup2(fds[1], a.fd);
    close(fds[1]);
    fds[1] = -1;
    if (r == -1) {
	ret = -5;
	goto err;
    }
    if (getfd != 1)
	fcntl(a.fd, F_SETFD, getfd);
    if (getfl & O_NONBLOCK)
	(void)tls_socket_nonblocking(a.fd);
    if (a.infofd != NULL)
	*a.infofd = infofds[0];
    return 0;
    
  err:
    if (fds[0] != -1)
	close(fds[0]);
    if (fds[1] != -1)
	close(fds[1]);
    if (infofds[0] != -1)
	close(infofds[0]);
    if (infofds[1] != -1)
	close(infofds[1]);
    return ret;
}

/*****************************************************************************/

static char errbuf[TLS_ERROR_BUFSIZ];
static size_t errbuf_i = 0;

static void
tls_errflush(void *apparg)
{
    if (errbuf_i == 0)
	return;
    
    assert(errbuf_i < sizeof errbuf);
    assert(errbuf[errbuf_i] == 0);
    if (errbuf_i == sizeof errbuf - 1) {
	/* make sure we have a newline, even if string has been truncated */
	errbuf[errbuf_i - 1] = '\n';
    }

    /* TLS_APP_ERRFLUSH may modify the string as needed,
     * e.g. substitute other characters for \n for convenience */
    TLS_APP_ERRFLUSH(tls_child_p, errbuf, errbuf_i, apparg);

    errbuf_i = 0;
}

static void
tls_errprintf(int flush, void *apparg, const char *fmt, ...)
{
    va_list args;
    int r;
    
    if (errbuf_i < sizeof errbuf - 1) {
	size_t n;

	va_start(args, fmt);
	n = (sizeof errbuf) - errbuf_i;
	r = vsnprintf(errbuf + errbuf_i, n, fmt, args);
	if (r >= n)
	    r = n - 1;
	if (r >= 0) {
	    errbuf_i += r;
	} else {
	    errbuf_i = sizeof errbuf - 1;
	    errbuf[errbuf_i] = '\0';
	}
	assert(errbuf_i < sizeof errbuf);
	assert(errbuf[errbuf_i] == 0);
    }
#ifndef TLS_CUMULATE_ERRORS
    tls_errflush(apparg);
#else
    if (flush)
	tls_errflush(apparg);
#endif
}

/* app_prefix.. are for additional information provided by caller.
 * If OpenSSL error queue is empty, print default_text ("???" if NULL).
 */
static char *
tls_openssl_errors(const char *app_prefix_1, const char *app_prefix_2, const char *default_text, void *apparg)
{
    static char reasons[255];
    size_t reasons_i;
    unsigned long err;
    const char *file;
    int line;
    const char *data;
    int flags;
    char *errstring;
    int printed_something = 0;
    
    reasons_i = 0;

    assert(app_prefix_1 != NULL);
    assert(app_prefix_2 != NULL);

    if (default_text == NULL)
	default_text = "?""?""?";
    
    while ((err = ERR_get_error_line_data(&file,&line,&data,&flags)) != 0) {
	if (reasons_i < sizeof reasons) {
	    size_t n;
	    int r;

	    n = (sizeof reasons) - reasons_i;
	    r = snprintf(reasons + reasons_i, n, "%s%s", (reasons_i > 0 ? ", " : ""), ERR_reason_error_string(err));
	    if (r >= n)
		r = n - 1;
	    if (r >= 0) {
		reasons_i += r;
	    } else {
		reasons_i = sizeof reasons;
	    }
	    assert(reasons_i <= sizeof reasons);
	}
	
	errstring = ERR_error_string(err, NULL);
	assert(errstring != NULL);
	tls_errprintf(0, apparg, "OpenSSL error%s%s: %s:%s:%d:%s\n", app_prefix_1, app_prefix_2, errstring, file, line, (flags & ERR_TXT_STRING) ? data : "");
	printed_something = 1;
    }

    if (!printed_something) {
	assert(reasons_i == 0);
	snprintf(reasons, sizeof reasons, "%s", default_text);
	tls_errprintf(0, apparg, "OpenSSL error%s%s: %s\n", app_prefix_1, app_prefix_2, default_text);
    }

#ifdef TLS_CUMULATE_ERRORS    
    tls_errflush(apparg);
#endif
    assert(errbuf_i == 0);

    return reasons;
}

/*****************************************************************************/

static int tls_init_done = 0;

static int
tls_init(void *apparg)
{
    if (tls_init_done)
	return 0;
    
    SSL_load_error_strings();
    if (!SSL_library_init() /* aka SSLeay_add_ssl_algorithms() */ ) {
	tls_errprintf(1, apparg, "SSL_library_init failed.\n");
	return -1;
    }
    tls_init_done = 1;
    tls_rand_seed();
    return 0;
}

/*****************************************************************************/

static void
tls_rand_seed_uniquely(void)
{
    struct {
	pid_t pid;
	time_t time;
	void *stack;
    } data;

    data.pid = getpid();
    data.time = time(NULL);
    data.stack = (void *)&data;

    RAND_seed((const void *)&data, sizeof data);
}

void
tls_rand_seed(void)
{
    struct {
	struct utsname uname;
	int uname_1;
	int uname_2;
	uid_t uid;
	uid_t euid;
	gid_t gid;
	gid_t egid;
    } data;
    
    data.uname_1 = uname(&data.uname);
    data.uname_2 = errno; /* Let's hope that uname fails randomly :-) */

    data.uid = getuid();
    data.euid = geteuid();
    data.gid = getgid();
    data.egid = getegid();
    
    RAND_seed((const void *)&data, sizeof data);
    tls_rand_seed_uniquely();
}

static int tls_rand_seeded_p = 0;

#define my_MIN_SEED_BYTES 256 /* struct stat can be larger than 128 */
int
tls_rand_seed_from_file(const char *filename, size_t n, void *apparg)
{
    /* Seed OpenSSL's random number generator from file.
       Try to read n bytes if n > 0, whole file if n == 0. */

    int r;

    if (tls_init(apparg) == -1)
	return -1;
    tls_rand_seed();

    r = RAND_load_file(filename, (n > 0 && n < LONG_MAX) ? (long)n : LONG_MAX);
    /* r is the number of bytes filled into the random number generator,
     * which are taken from "stat(filename, ...)" in addition to the
     * file contents.
     */
    assert(1 < my_MIN_SEED_BYTES);
    /* We need to detect at least those cases when the file does not exist
     * at all.  With current versions of OpenSSL, this should do it: */
    if (n == 0)
	n = my_MIN_SEED_BYTES;
    if (r < n) {
	tls_errprintf(1, apparg, "rand_seed_from_file: could not read %d bytes from %s.\n", n, filename);
	return -1;
    } else {
	tls_rand_seeded_p = 1;
	return 0;
    }
}

void
tls_rand_seed_from_memory(const void *buf, size_t n)
{
    size_t i = 0;
    
    while (i < n) {
	size_t rest = n - i;
	int chunk = rest < INT_MAX ? (int)rest : INT_MAX;
	RAND_seed((const char *)buf + i, chunk);
	i += chunk;
    }
    tls_rand_seeded_p = 1;
}


/*****************************************************************************/

struct tls_x509_name_string {
    char str[100];
};

static void
tls_get_x509_subject_name_oneline(X509 *cert, struct tls_x509_name_string *namestring)
{
    X509_NAME *name;

    if (cert == NULL) {
	namestring->str[0] = '\0';
	return;
    }
    
    name = X509_get_subject_name(cert); /* does not increment any reference counter */

    assert(sizeof namestring->str >= 4); /* "?" or "...", plus 0 */
    
    if (name == NULL) {
	namestring->str[0] = '?';
	namestring->str[1] = 0;
    } else {
	size_t len;

	X509_NAME_oneline(name, namestring->str, sizeof namestring->str);
	len = strlen(namestring->str);
	assert(namestring->str[len] == 0);
	assert(len < sizeof namestring->str);

	if (len+1 == sizeof namestring->str) {
	    /* (Probably something was cut off.)
	     * Does not really work -- X509_NAME_oneline truncates after
	     * name components, we cannot tell from the result whether
	     * anything is missing. */

	    assert(namestring->str[len] == 0);
	    namestring->str[--len] = '.';
	    namestring->str[--len] = '.';
	    namestring->str[--len] = '.';
	}
    }
}

/*****************************************************************************/

/* to hinder OpenSSL from asking for passphrases */
static int
no_passphrase_callback(char *buf, int num, int w, void *arg)
{
    return -1;
}

#if OPENSSL_VERSION_NUMBER >= 0x00907000L
static int
verify_dont_fail_cb(X509_STORE_CTX *c, void *unused_arg)
#else
static int
verify_dont_fail_cb(X509_STORE_CTX *c)
#endif
{
    int i;
    
    i = X509_verify_cert(c); /* sets c->error */
#if OPENSSL_VERSION_NUMBER >= 0x00905000L /* don't allow unverified
					   * certificates -- they could
					   * survive session reuse, but
					   * OpenSSL < 0.9.5-dev does not
					   * preserve their verify_result */
    if (i == 0)
	return 1;
    else
#endif
	return i;
}

static DH *tls_dhe1024 = NULL; /* generating these takes a while, so do it just once */

void
tls_set_dhe1024(int i, void *apparg)
{
    DSA *dsaparams;
    DH *dhparams;
    const char *seed[] = { ";-)  :-(  :-)  :-(  ",
			   ";-)  :-(  :-)  :-(  ",
			   "Random String no. 12",
			   ";-)  :-(  :-)  :-(  ",
			   "hackers have even mo", /* from jargon file */
    };
    unsigned char seedbuf[20];
    
    tls_init(apparg);
    if (i >= 0) {
	i %= sizeof seed / sizeof seed[0];
	assert(strlen(seed[i]) == 20);
	memcpy(seedbuf, seed[i], 20);
	dsaparams = DSA_generate_parameters(1024, seedbuf, 20, NULL, NULL, 0, NULL);
    } else {
	/* random parameters (may take a while) */
	dsaparams = DSA_generate_parameters(1024, NULL, 0, NULL, NULL, 0, NULL);
    }
    
    if (dsaparams == NULL) {
	tls_openssl_errors("", "", NULL, apparg);
	return;
    }
    dhparams = DSA_dup_DH(dsaparams);
    DSA_free(dsaparams);
    if (dhparams == NULL) {
	tls_openssl_errors("", "", NULL, apparg);
	return;
    }
    if (tls_dhe1024 != NULL)
	DH_free(tls_dhe1024);
    tls_dhe1024 = dhparams;
}

struct tls_create_ctx_args
tls_create_ctx_defaultargs(void)
{
	struct tls_create_ctx_args ret;

	ret.client_p = 0;
	ret.certificate_file = NULL;
	ret.key_file = NULL;
	ret.ca_file = NULL;
	ret.verify_depth = -1;
	ret.fail_unless_verified = 0;
	ret.export_p = 0;

	return ret;
}

SSL_CTX *
tls_create_ctx(struct tls_create_ctx_args a, void *apparg)
{
    int r;
    static long context_num = 0;
    SSL_CTX *ret;
    const char *err_pref_1 = "", *err_pref_2 = "";
    
    if (tls_init(apparg) == -1)
	return NULL;

    ret = SSL_CTX_new((a.client_p? SSLv23_client_method:SSLv23_server_method)());

    if (ret == NULL)
	goto err;

    SSL_CTX_set_default_passwd_cb(ret, no_passphrase_callback);
    SSL_CTX_set_mode(ret, SSL_MODE_ENABLE_PARTIAL_WRITE);
    
    if ((a.certificate_file != NULL) || (a.key_file != NULL)) {
	if (a.key_file == NULL) {
	    tls_errprintf(1, apparg, "Need a key file.\n");
	    goto err_return;
	}
	if (a.certificate_file == NULL) {
	    tls_errprintf(1, apparg, "Need a certificate chain file.\n");
	    goto err_return;
	}
	
	if (!SSL_CTX_use_PrivateKey_file(ret, a.key_file, SSL_FILETYPE_PEM))
	    goto err;
	if (!tls_rand_seeded_p) {
	    /* particularly paranoid people may not like this --
	     * so provide your own random seeding before calling this */
	    if (tls_rand_seed_from_file(a.key_file, 0, apparg) == -1)
		goto err_return;
	}
	if (!SSL_CTX_use_certificate_chain_file(ret, a.certificate_file))
	    goto err;
	if (!SSL_CTX_check_private_key(ret)) {
	    tls_errprintf(1, apparg, "Private key \"%s\" does not match certificate \"%s\".\n", a.key_file, a.certificate_file);
	    goto err_peek;
	}
    }
    
    if ((a.ca_file != NULL) || (a.verify_depth > 0)) {
	context_num++;
	r = SSL_CTX_set_session_id_context(ret, (const void *)&context_num, (unsigned int)sizeof context_num);
	if (!r)
	    goto err;
	
	SSL_CTX_set_verify(ret, SSL_VERIFY_PEER | (a.fail_unless_verified ? SSL_VERIFY_FAIL_IF_NO_PEER_CERT : 0), 0);
	if (!a.fail_unless_verified)
	    SSL_CTX_set_cert_verify_callback(ret, verify_dont_fail_cb, NULL);
	    
	if (a.verify_depth > 0)
	    SSL_CTX_set_verify_depth(ret, a.verify_depth);
	
	if (a.ca_file != NULL) {
	    r = SSL_CTX_load_verify_locations(ret, a.ca_file, NULL /* no CA-directory */); /* does not report failure if file does not exist ... */
	    if (!r) {
		err_pref_1 = " while processing certificate file ";
		err_pref_2 = a.ca_file;
		goto err;
	    }
	    
	    if (!a.client_p) {
		/* SSL_load_client_CA_file is a misnomer, it just creates a list of CNs. */
		SSL_CTX_set_client_CA_list(ret, SSL_load_client_CA_file(a.ca_file));
		/* SSL_CTX_set_client_CA_list does not have a return value;
		 * it does not really need one, but make sure
		 * (we really test if SSL_load_client_CA_file worked) */
		if (SSL_CTX_get_client_CA_list(ret) == NULL) {
		    tls_errprintf(1, apparg, "Could not set client CA list from \"%s\".\n", a.ca_file);
		    goto err_peek;
		}
	    }
	}
    }
    
    if (!a.client_p) {
	if (tls_dhe1024 == NULL) {
	    int i;

	    RAND_bytes((unsigned char *) &i, sizeof i);
	    /* make sure that i is non-negative -- pick one of the provided
	     * seeds */
	    if (i < 0)
		i = -i;
	    if (i < 0)
		i = 0;
	    tls_set_dhe1024(i, apparg);
	    if (tls_dhe1024 == NULL)
		goto err_return;
	}
	
	if (!SSL_CTX_set_tmp_dh(ret, tls_dhe1024))
	    goto err;

	/* avoid small subgroup attacks: */
	SSL_CTX_set_options(ret, SSL_OP_SINGLE_DH_USE);
    }
	
#ifndef NO_RSA
    if (!a.client_p && a.export_p) {
	RSA *tmpkey;

	tmpkey = RSA_generate_key(512, RSA_F4, 0, NULL);
	if (tmpkey == NULL)
	    goto err;
	if (!SSL_CTX_set_tmp_rsa(ret, tmpkey)) {
	    RSA_free(tmpkey);
	    goto err;
	}
	RSA_free(tmpkey); /* SSL_CTX_set_tmp_rsa uses a duplicate. */
    }
#endif
	
    return ret;
    
 err_peek:
    if (!ERR_peek_error())
	goto err_return;
 err:
    tls_openssl_errors(err_pref_1, err_pref_2, NULL, apparg);
 err_return:
    if (ret != NULL)
	SSL_CTX_free(ret);
    return NULL;
}


/*****************************************************************************/

static int
tls_socket_nonblocking(int fd)
{
    int v, r;

    v = fcntl(fd, F_GETFL, 0);
    if (v == -1) {
	if (errno == EINVAL)
	    return 0; /* already shut down -- ignore */
	return -1;
    }
    r = fcntl(fd, F_SETFL, v | O_NONBLOCK);
    if (r == -1) {
	if (errno == EINVAL)
	    return 0; /* already shut down -- ignore */
	return -1;
    }
    return 0;
}

static int
max(int a, int b)
{
    return a > b ? a : b;
}

static void
tls_sockets_select(int read_select_1, int read_select_2, int write_select_1, int write_select_2, int seconds /* timeout, -1 means no timeout */)
{
    int maxfd, n;
    fd_set reads, writes;
    struct timeval timeout;
    struct timeval *timeout_p;
    
    assert(read_select_1 >= -1 && read_select_2 >= -1 && write_select_1 >= -1 && write_select_2 >= -1);
    assert(read_select_1 < FD_SETSIZE && read_select_2 < FD_SETSIZE -1 && write_select_1 < FD_SETSIZE -1 && write_select_2 < FD_SETSIZE -1);

    maxfd = max(max(read_select_1, read_select_2), max(write_select_1, write_select_2));
    assert(maxfd >= 0);

    FD_ZERO(&reads);
    FD_ZERO(&writes);
    
    for(n = 0; n < 4; ++n) {
	int i = n % 2;
	int w = n >= 2;
	/* loop over all (i, w) in {0,1}x{0,1} */
	int fd;
	
	if (i == 0 && w == 0)
	    fd = read_select_1;
	else if (i == 1 && w == 0)
	    fd = read_select_2;
	else if (i == 0 && w == 1)
	    fd = write_select_1;
	else {
	    assert(i == 1 && w == 1);
	    fd = write_select_2;
	}
	
	if (fd >= 0) {
	    if (w == 0)
		FD_SET(fd, &reads);
	    else /* w == 1 */
		FD_SET(fd, &writes);
	}
    }

    if (seconds >= 0) {
	timeout.tv_sec = seconds;
	timeout.tv_usec = 0;
	timeout_p = &timeout;
    } else 
	timeout_p = NULL;

    DEBUG_MSG2("select no.", ++tls_select_count);
    select(maxfd + 1, &reads, &writes, (fd_set *) NULL, timeout_p);
    DEBUG_MSG("cont.");
}

/*****************************************************************************/

#define TUNNELBUFSIZE (16*1024)
struct tunnelbuf {
    char buf[TUNNELBUFSIZE];
    size_t len;
    size_t offset;
};

static int tls_connect_attempt(SSL *, int *write_select, int *read_select, int *closed, int *progress, const char **err_pref);

static int tls_accept_attempt(SSL *, int *write_select, int *read_select, int *closed, int *progress, const char **err_pref);

static int tls_write_attempt(SSL *, struct tunnelbuf *, int *write_select, int *read_select, int *closed, int *progress, const char **err_pref);

static int tls_read_attempt(SSL *, struct tunnelbuf *, int *write_select, int *read_select, int *closed, int *progress, const char **err_pref);

static int write_attempt(int fd, struct tunnelbuf *, int *select, int *closed, int *progress);

static int read_attempt(int fd, struct tunnelbuf *, int *select, int *closed, int *progress);

static void write_info(SSL *ssl, int *info_fd)
{
    if (*info_fd != -1) {
	long v;
	int v_ok;
	struct tls_x509_name_string peer;
	char infobuf[TLS_INFO_SIZE];
	int r;

	DEBUG_MSG("write_info");
	v = SSL_get_verify_result(ssl);
	v_ok = (v == X509_V_OK) ? 'A' : 'E'; /* Auth./Error */
	{
	    X509 *peercert;

	    peercert = SSL_get_peer_certificate(ssl);
	    tls_get_x509_subject_name_oneline(peercert, &peer);
	    if (peercert != NULL)
		X509_free(peercert);
	}
	if (peer.str[0] == '\0')
	    v_ok = '0'; /* no cert at all */
	else
	    if (strchr(peer.str, '\n')) {
		/* should not happen, but make sure */
		*strchr(peer.str, '\n') = '\0';
	    }
	r = snprintf(infobuf, sizeof infobuf, "%c:%s\n%s\n", v_ok, X509_verify_cert_error_string(v), peer.str);
	DEBUG_MSG2("snprintf", r);
	if (r == -1 || r >= sizeof infobuf)
	    r = sizeof infobuf - 1;
	write(*info_fd, infobuf, r);
	close (*info_fd);
	*info_fd = -1;
    }
}


/* tls_proxy expects that all fds are closed after return */
static void
tls_proxy(int clear_fd, int tls_fd, int info_fd, SSL_CTX *ctx, int client_p)
{
    struct tunnelbuf clear_to_tls, tls_to_clear;
    SSL *ssl;
    BIO *rbio, *wbio;
    int closed, in_handshake;
    const char *err_pref_1 = "", *err_pref_2 = "";
    const char *err_def = NULL;

    assert(clear_fd != -1);
    assert(tls_fd != -1);
    assert(clear_fd < FD_SETSIZE);
    assert(tls_fd < FD_SETSIZE);
    /* info_fd may be -1 */
    assert(ctx != NULL);

    tls_rand_seed_uniquely();

    tls_socket_nonblocking(clear_fd);
    DEBUG_MSG2("clear_fd", clear_fd);
    tls_socket_nonblocking(tls_fd);
    DEBUG_MSG2("tls_fd", tls_fd);

    ssl = SSL_new(ctx);
    if (ssl == NULL)
	goto err;
    DEBUG_MSG("SSL_new");
    if (!SSL_set_fd(ssl, tls_fd))
	goto err;
    rbio = SSL_get_rbio(ssl);
    wbio = SSL_get_wbio(ssl); /* should be the same, but who cares */
    assert(rbio != NULL);
    assert(wbio != NULL);
    if (client_p)
	SSL_set_connect_state(ssl);
    else
	SSL_set_accept_state(ssl);
    
    closed = 0;
    in_handshake = 1;
    tls_to_clear.len = 0;
    tls_to_clear.offset = 0;
    clear_to_tls.len = 0;
    clear_to_tls.offset = 0;

    err_def = "I/O error";
    
    /* loop finishes as soon as we detect that one side closed;
     * when all (program and OS) buffers have enough space,
     * the data from the last succesful read in each direction is transferred
     * before close */
    do {
	int clear_read_select = 0, clear_write_select = 0,
	    tls_read_select = 0, tls_write_select = 0,
	    progress = 0;
	int r;
	unsigned long num_read = BIO_number_read(rbio),
	    num_written = BIO_number_written(wbio);

	DEBUG_MSG2("loop iteration", ++tls_loop_count);

	if (in_handshake) {
	    DEBUG_MSG("in_handshake");
	    if (client_p)
		r = tls_connect_attempt(ssl, &tls_write_select, &tls_read_select, &closed, &progress, &err_pref_1);
	    else
		r = tls_accept_attempt(ssl, &tls_write_select, &tls_read_select, &closed, &progress, &err_pref_1);
	    if (r != 0) {
		write_info(ssl, &info_fd);
		goto err;
	    }
	    if (closed)
		goto err_return;
	    if (!SSL_in_init(ssl)) {
		in_handshake = 0;
		write_info(ssl, &info_fd);