/*++
/* NAME
/*	smtp_session 3
/* SUMMARY
/*	SMTP_SESSION structure management
/* SYNOPSIS
/*	#include "smtp.h"
/*
/*	SMTP_SESSION *smtp_session_alloc(stream, dest, host, addr, port, flags)
/*	VSTREAM *stream;
/*	char	*dest;
/*	char	*host;
/*	char	*addr;
/*	unsigned port;
/*	int	flags;
/*
/*	void	smtp_session_free(session)
/*	SMTP_SESSION *session;
/*
/*	int	smtp_session_passivate(session, dest_prop, endp_prop)
/*	SMTP_SESSION *session;
/*	VSTRING	*dest_prop;
/*	VSTRING	*endp_prop;
/*
/*	SMTP_SESSION *smtp_session_activate(fd, dest_prop, endp_prop)
/*	int	fd;
/*	VSTRING	*dest_prop;
/*	VSTRING	*endp_prop;
/* DESCRIPTION
/*	smtp_session_alloc() allocates memory for an SMTP_SESSION structure
/*	and initializes it with the given stream and destination, host name
/*	and address information.  The host name and address strings are
/*	copied. The port is in network byte order.
/*	When TLS is enabled, smtp_session_alloc() looks up the
/*	per-site TLS policies for TLS enforcement and certificate
/*	verification.  The resulting policy is stored into the
/*	SMTP_SESSION object.
/*
/*	smtp_session_free() destroys an SMTP_SESSION structure and its
/*	members, making memory available for reuse. It will handle the
/*	case of a null stream and will assume it was given a different
/*	purpose.
/*
/*	smtp_session_passivate() flattens an SMTP session so that
/*	it can be cached. The SMTP_SESSION structure is destroyed.
/*
/*	smtp_session_activate() inflates a flattened SMTP session
/*	so that it can be used. The input is modified.
/*
/*	Arguments:
/* .IP stream
/*	A full-duplex stream.
/* .IP dest
/*	The unmodified next-hop or fall-back destination including
/*	the optional [] and including the optional port or service.
/* .IP host
/*	The name of the host that we are connected to.
/* .IP addr
/*	The address of the host that we are connected to.
/* .IP port
/*	The remote port, network byte order.
/* .IP flags
/*	Zero or more of the following:
/* .RS
/* .IP SMTP_SESS_FLAG_CACHE
/*	Enable session caching.
/* .RE
/* .IP
/*	The manifest constant SMTP_SESS_FLAG_NONE requests no options.
/* .IP dest_prop
/*	Destination specific session properties: the server is the
/*	best MX host for the current logical destination.
/* .IP endp_prop
/*	Endpoint specific session properties: all the features
/*	advertised by the remote server.
/* LICENSE
/* .ad
/* .fi
/*	The Secure Mailer license must be distributed with this software.
/* AUTHOR(S)
/*	Wietse Venema
/*	IBM T.J. Watson Research
/*	P.O. Box 704
/*	Yorktown Heights, NY 10598, USA
/*
/*	TLS support originally by:
/*	Lutz Jaenicke
/*	BTU Cottbus
/*	Allgemeine Elektrotechnik
/*	Universitaetsplatz 3-4
/*	D-03044 Cottbus, Germany
/*--*/

/* System library. */

#include <sys_defs.h>
#include <stdlib.h>
#include <string.h>
#include <netinet/in.h>

#ifdef STRCASECMP_IN_STRINGS_H
#include <strings.h>
#endif

/* Utility library. */

#include <msg.h>
#include <mymalloc.h>
#include <vstream.h>
#include <stringops.h>

/* Global library. */

#include <mime_state.h>
#include <debug_peer.h>
#include <mail_params.h>
#include <maps.h>

/* Application-specific. */

#include "smtp.h"
#include "smtp_sasl.h"

#define STR(x) vstring_str(x)

/*#define msg_verbose 1*/

#ifdef USE_TLS

 /*
  * TLS enforcement level. Actual TLS policies will be NONE or higher.
  * 
  * There are two pseudo levels: NOTFOUND is a sentinel value for the ease of
  * implementation; MAY is a wild-card that indicates "anything goes".
  * 
  * Non pseudo levels can also be used to indicate the actual security level of
  * a session.
  */
#define SMTP_TLS_LEV_NOTFOUND	(-1)	/* sentinel */
#define SMTP_TLS_LEV_NONE	0	/* plain-text only */
#define SMTP_TLS_LEV_MAY	1	/* wildcard */
#define SMTP_TLS_LEV_ENCRYPT	2	/* encrypted connection */
#define SMTP_TLS_LEV_VERIFY	3	/* certificate verified */
#define SMTP_TLS_LEV_STRICT	4	/* "secure" verification */

static MAPS *tls_per_site;		/* lookup table(s) */

/* smtp_tls_list_init - initialize per-site policy lists */

void    smtp_tls_list_init(void)
{
    tls_per_site = maps_create(VAR_SMTP_TLS_PER_SITE, var_smtp_tls_per_site,
			       DICT_FLAG_LOCK);
}

/* smtp_tls_policy_print - print policy level */

static void smtp_tls_policy_print(const char *name, int level)
{
    msg_info("%s TLS level: %s", name,
	     level == SMTP_TLS_LEV_VERIFY ? "verify" :
	     level == SMTP_TLS_LEV_ENCRYPT ? "encrypt" :
	     level == SMTP_TLS_LEV_MAY ? "may" :
	     level == SMTP_TLS_LEV_NONE ? "none" :
	     "unknown");
}

/* smtp_tls_site_policy - look up per-site TLS policy */

static void smtp_tls_site_policy(int *site_level,
				         const char *site_name,
				         const char *site_class)
{
    const char *lookup;
    char   *lookup_key;

    /*
     * Look up a non-default policy. In case of multiple lookup results, the
     * precedence order is a permutation of the TLS enforcement level order:
     * VERIFY, ENCRYPT, NONE, MAY, NOTFOUND. I.e. we override MAY with a more
     * specific policy including NONE, otherwise we choose the stronger
     * enforcement level.
     */
    lookup_key = lowercase(mystrdup(site_name));
    if ((lookup = maps_find(tls_per_site, lookup_key, 0)) != 0) {
	if (!strcasecmp(lookup, "NONE")) {
	    /* NONE overrides MAY or NOTFOUND. */
	    if (*site_level <= SMTP_TLS_LEV_MAY)
		*site_level = SMTP_TLS_LEV_NONE;
	} else if (!strcasecmp(lookup, "MAY")) {
	    /* MAY overrides NOTFOUND but not NONE. */
	    if (*site_level < SMTP_TLS_LEV_NONE)
		*site_level = SMTP_TLS_LEV_MAY;
	} else if (!strcasecmp(lookup, "MUST_NOPEERMATCH")) {
	    if (*site_level < SMTP_TLS_LEV_ENCRYPT)
		*site_level = SMTP_TLS_LEV_ENCRYPT;
	} else if (!strcasecmp(lookup, "MUST")) {
	    if (*site_level < SMTP_TLS_LEV_VERIFY)
		*site_level = SMTP_TLS_LEV_VERIFY;
	} else {
	    msg_warn("Table %s: ignoring unknown TLS policy '%s' for %s %s",
		     var_smtp_tls_per_site, lookup, site_class, site_name);
	}
    }
    myfree(lookup_key);
}

/* smtp_tls_level_init - configure session TLS enforcement level */

static int smtp_tls_level_init(const char *dest, const char *host)
{
    int     global_level;
    int     site_level;
    int     tls_level;

    /*
     * Compute the global TLS policy. This is the default policy level when
     * no per-site policy exists. It also is used to override a wild-card
     * per-site policy.
     */
    if (var_smtp_enforce_tls)
	global_level = var_smtp_tls_enforce_peername ?
	    SMTP_TLS_LEV_VERIFY : SMTP_TLS_LEV_ENCRYPT;
    else
	global_level = var_smtp_use_tls ?
	    SMTP_TLS_LEV_MAY : SMTP_TLS_LEV_NONE;
    if (msg_verbose)
	smtp_tls_policy_print("global", global_level);

    /*
     * Compute the per-site TLS enforcement level. For compatibility with the
     * original TLS patch, this algorithm is gives equal precedence to host
     * and next-hop policies.
     */
    site_level = SMTP_TLS_LEV_NOTFOUND;

    if (tls_per_site) {
	smtp_tls_site_policy(&site_level, dest, "next-hop destination");
	if (strcasecmp(dest, host) != 0)
	    smtp_tls_site_policy(&site_level, host, "server hostname");
	if (msg_verbose)
	    smtp_tls_policy_print("site", site_level);
    }

    /*
     * Override a wild-card per-site policy with a more specific global
     * policy.
     * 
     * With the original TLS patch, 1) a per-site ENCRYPT could not override a
     * global VERIFY, and 2) a combined per-site (NONE+MAY) policy produced
     * inconsistent results: it changed a global VERIFY into NONE, while
     * producing MAY with all weaker global policy settings.
     * 
     * With the current implementation, a combined per-site (NONE+MAY)
     * consistently overrides global policy with NONE, and global policy can
     * override only a per-site MAY wildcard. That is, specific policies
     * consistently override wildcard policies, and (non-wildcard) per-site
     * policies consistently override global policies.
     */
    if (site_level == SMTP_TLS_LEV_NOTFOUND
	|| (site_level == SMTP_TLS_LEV_MAY
	    && global_level > SMTP_TLS_LEV_MAY))
	tls_level = global_level;
    else
	tls_level = site_level;

    if (msg_verbose && tls_per_site)
	smtp_tls_policy_print("effective", tls_level);

    return (tls_level);
}

#endif

/* smtp_session_alloc - allocate and initialize SMTP_SESSION structure */

SMTP_SESSION *smtp_session_alloc(VSTREAM *stream, const char *dest,
				         const char *host, const char *addr,
				         unsigned port, int flags)
{
    SMTP_SESSION *session;

    session = (SMTP_SESSION *) mymalloc(sizeof(*session));
    session->stream = stream;
    session->dest = mystrdup(dest);
    session->host = mystrdup(host);
    session->addr = mystrdup(addr);
    session->namaddr = concatenate(host, "[", addr, "]", (char *) 0);
    session->helo = 0;
    session->port = port;
    session->features = 0;

    session->size_limit = 0;
    session->error_mask = 0;
    session->buffer = vstring_alloc(100);
    session->scratch = vstring_alloc(100);
    session->scratch2 = vstring_alloc(100);
    smtp_chat_init(session);
    session->features = 0;
    session->mime_state = 0;

    session->sndbufsize = 0;
    session->send_proto_helo = 0;

    if (flags & SMTP_SESS_FLAG_CACHE)
	session->reuse_count = var_smtp_reuse_limit;
    else
	session->reuse_count = 0;

#ifdef USE_SASL_AUTH
    smtp_sasl_connect(session);
#endif

#ifdef USE_TLS
    session->tls_use_tls = session->tls_enforce_tls = 0;
    session->tls_enforce_peername = 0;
    session->tls_context = 0;
    session->tls_info = tls_info_zero;
    switch (smtp_tls_level_init(dest, host)) {
    case SMTP_TLS_LEV_VERIFY:
	session->tls_enforce_peername = 1;
    case SMTP_TLS_LEV_ENCRYPT:
	session->tls_enforce_tls = 1;
    case SMTP_TLS_LEV_MAY:
	session->tls_use_tls = 1;
	break;
    }
#endif
    debug_peer_check(host, addr);
    return (session);
}

/* smtp_session_free - destroy SMTP_SESSION structure and contents */

void    smtp_session_free(SMTP_SESSION *session)
{
#ifdef USE_TLS
    if (session->stream) {
	vstream_fflush(session->stream);
	if (session->tls_context)
	    tls_client_stop(smtp_tls_ctx, session->stream,
			    var_smtp_starttls_tmout, 0,
			    &(session->tls_info));
    }
#endif
    if (session->stream)
	vstream_fclose(session->stream);
    myfree(session->dest);
    myfree(session->host);
    myfree(session->addr);
    myfree(session->namaddr);
    if (session->helo)
	myfree(session->helo);

    vstring_free(session->buffer);
    vstring_free(session->scratch);
    vstring_free(session->scratch2);

    if (session->history)
	smtp_chat_reset(session);
    if (session->mime_state)
	mime_state_free(session->mime_state);

#ifdef USE_SASL_AUTH
    smtp_sasl_cleanup(session);
#endif

    debug_peer_restore();
    myfree((char *) session);
}

/* smtp_session_passivate - passivate an SMTP_SESSION object */

int     smtp_session_passivate(SMTP_SESSION *session, VSTRING *dest_prop,
			               VSTRING *endp_prop)
{
    int     fd;

    /*
     * Encode the local-to-physical binding properties: whether or not this
     * server is best MX host for the next-hop or fall-back logical
     * destination (this information is needed for loop handling in
     * smtp_proto()).
     * 
     * XXX It would be nice to have a VSTRING to VSTREAM adapter so that we can
     * serialize the properties with attr_print() instead of using ad-hoc,
     * non-reusable, code and hard-coded format strings.
     */
    vstring_sprintf(dest_prop, "%u",
		    session->features & SMTP_FEATURE_DESTINATION_MASK);

    /*
     * Encode the physical endpoint properties: all the session properties
     * except for "session from cache", "best MX", or "RSET failure".
     * 
     * XXX It would be nice to have a VSTRING to VSTREAM adapter so that we can
     * serialize the properties with attr_print() instead of using obscure
     * hard-coded format strings.
     * 
     * XXX Should also record an absolute time when a session must be closed,
     * how many non-delivering mail transactions there were during this
     * session, and perhaps other statistics, so that we don't reuse a
     * session too much.
     */
    vstring_sprintf(endp_prop, "%s\n%s\n%s\n%u\n%u\n%u\n%u",
		    session->dest, session->host,
		    session->addr, session->port,
		    session->features & SMTP_FEATURE_ENDPOINT_MASK,
		    session->reuse_count,
		    session->sndbufsize);

    /*
     * Append the passivated SASL attributes.
     */
#ifdef USE_SASL
    if (smtp_sasl_enable)
	smtp_sasl_passivate(endp_prop, session);
#endif

    /*
     * Salvage the underlying file descriptor, and destroy the session
     * object.
     */
    fd = vstream_fileno(session->stream);
    vstream_fdclose(session->stream);
    session->stream = 0;
    smtp_session_free(session);

    return (fd);
}

/* smtp_session_activate - re-activate a passivated SMTP_SESSION object */

SMTP_SESSION *smtp_session_activate(int fd, VSTRING *dest_prop,
				            VSTRING *endp_prop)
{
    const char *myname = "smtp_session_activate";
    SMTP_SESSION *session;
    char   *dest_props;
    char   *endp_props;
    const char *prop;
    const char *dest;
    const char *host;
    const char *addr;
    unsigned port;
    unsigned features;			/* server features */
    unsigned reuse_count;		/* how reuses left */
    unsigned sndbufsize;		/* PIPELINING buffer size */

    /*
     * XXX it would be nice to have a VSTRING to VSTREAM adapter so that we
     * can de-serialize the properties with attr_scan(), instead of using
     * ad-hoc, non-reusable code.
     * 
     * XXX As a preliminary solution we use mystrtok(), but that function is not
     * suitable for zero-length fields.
     */
    endp_props = STR(endp_prop);
    if ((dest = mystrtok(&endp_props, "\n")) == 0) {
	msg_warn("%s: missing cached session destination property", myname);
	return (0);
    }
    if ((host = mystrtok(&endp_props, "\n")) == 0) {
	msg_warn("%s: missing cached session hostname property", myname);
	return (0);
    }
    if ((addr = mystrtok(&endp_props, "\n")) == 0) {
	msg_warn("%s: missing cached session address property", myname);
	return (0);
    }
    if ((prop = mystrtok(&endp_props, "\n")) == 0 || !alldig(prop)) {
	msg_warn("%s: bad cached session port property", myname);
	return (0);
    }
    port = atoi(prop);

    if ((prop = mystrtok(&endp_props, "\n")) == 0 || !alldig(prop)) {
	msg_warn("%s: bad cached session features property", myname);
	return (0);
    }
    features = atoi(prop);

    if ((prop = mystrtok(&endp_props, "\n")) == 0 || !alldig(prop)) {
	msg_warn("%s: bad cached session reuse_count property", myname);
	return (0);
    }
    reuse_count = atoi(prop);

    if ((prop = mystrtok(&endp_props, "\n")) == 0 || !alldig(prop)) {
	msg_warn("%s: bad cached session sndbufsize property", myname);
	return (0);
    }
    sndbufsize = atoi(prop);

    if (dest_prop && VSTRING_LEN(dest_prop)) {
	dest_props = STR(dest_prop);
	if ((prop = mystrtok(&dest_props, "\n")) == 0 || !alldig(prop)) {
	    msg_warn("%s: bad cached destination features property", myname);
	    return (0);
	}
	features |= atoi(prop);
    }

    /*
     * Allright, bundle up what we have sofar.
     */
    session = smtp_session_alloc(vstream_fdopen(fd, O_RDWR),
			       dest, host, addr, port, SMTP_SESS_FLAG_NONE);
    session->features = (features | SMTP_FEATURE_FROM_CACHE);
    session->reuse_count = reuse_count - 1;
    session->sndbufsize = sndbufsize;

    if (msg_verbose)
	msg_info("%s: dest=%s host=%s addr=%s port=%u features=0x%x, reuse=%u, sndbuf=%u",
		 myname, dest, host, addr, ntohs(port), features, reuse_count, sndbufsize);

    /*
     * Re-activate the SASL attributes.
     */
#ifdef USE_SASL
    if (smtp_sasl_enable && smtp_sasl_activate(session, endp_props) < 0) {
	vstream_fdclose(session->stream);
	session->stream = 0;
	smtp_session_free(session);
	return (0);
    }
#endif

    return (session);
}
