smtpd_peer.c

[詳解]

/*++
/* NAME
/*  smtpd_peer 3
/* SUMMARY
/*  look up peer name/address information
/* SYNOPSIS
/*  #include "smtpd.h"
/*
/*  void    smtpd_peer_init(state)
/*  SMTPD_STATE *state;
/*
/*  void    smtpd_peer_reset(state)
/*  SMTPD_STATE *state;
/* DESCRIPTION
/*  The smtpd_peer_init() routine attempts to produce a printable
/*  version of the peer name and address of the specified socket.
/*  Where information is unavailable, the name and/or address
/*  are set to "unknown".
/*
/*  Alternatively, the peer address and port may be obtained
/*  from a proxy server.
/*
/*  This module uses the local name service via getaddrinfo()
/*  and getnameinfo(). It does not query the DNS directly.
/*
/*  smtpd_peer_init() updates the following fields:
/* .IP name
/*  The verified client hostname. This name is represented by
/*  the string "unknown" when 1) the address->name lookup failed,
/*  2) the name->address mapping fails, or 3) the name->address
/*  mapping does not produce the client IP address.
/* .IP reverse_name
/*  The unverified client hostname as found with address->name
/*  lookup; it is not verified for consistency with the client
/*  IP address result from name->address lookup.
/* .IP forward_name
/*  The unverified client hostname as found with address->name
/*  lookup followed by name->address lookup; it is not verified
/*  for consistency with the result from address->name lookup.
/*  For example, when the address->name lookup produces as
/*  hostname an alias, the name->address lookup will produce
/*  as hostname the expansion of that alias, so that the two
/*  lookups produce different names.
/* .IP addr
/*  Printable representation of the client address.
/* .IP namaddr
/*  String of the form: "name[addr]:port".
/* .IP rfc_addr
/*  String of the form "ipv4addr" or "ipv6:ipv6addr" for use
/*  in Received: message headers.
/* .IP dest_addr
/*  Server address, used by the Dovecot authentication server,
/*  available as Milter {daemon_addr} macro, and as server_address
/*  policy delegation attribute.
/* .IP dest_port
/*  Server port, available as Milter {daemon_port} macro, and
/*  as server_port policy delegation attribute.
/* .IP name_status
/*  The name_status result field specifies how the name
/*  information should be interpreted:
/* .RS
/* .IP 2
/*  The address->name lookup and name->address lookup produced
/*  the client IP address.
/* .IP 4
/*  The address->name lookup or name->address lookup failed
/*  with a recoverable error.
/* .IP 5
/*  The address->name lookup or name->address lookup failed
/*  with an unrecoverable error, or the result did not match
/*  the client IP address.
/* .RE
/* .IP reverse_name_status
/*  The reverse_name_status result field specifies how the
/*  reverse_name information should be interpreted:
/* .RS .IP 2
/*  The address->name lookup succeeded.
/* .IP 4
/*  The address->name lookup failed with a recoverable error.
/* .IP 5
/*  The address->name lookup failed with an unrecoverable error.
/* .RE .IP forward_name_status
/*  The forward_name_status result field specifies how the
/*  forward_name information should be interpreted:
/* .RS .IP 2
/*  The address->name and name->address lookup succeeded.
/* .IP 4
/*  The address->name lookup or name->address failed with a
/*  recoverable error.
/* .IP 5
/*  The address->name lookup or name->address failed with an
/*  unrecoverable error.
/* .RE
/* .PP
/*  smtpd_peer_reset() releases memory allocated by smtpd_peer_init().
/* LICENSE
/* .ad
/* .fi
/*  The Secure Mailer license must be distributed with this software.
/* AUTHOR(S)
/*  Wietse Venema
/*  IBM T.J. Watson Research
/*  P.O. Box 704
/*  Yorktown Heights, NY 10598, USA
/*
/*  Wietse Venema
/*  Google, Inc.
/*  111 8th Avenue
/*  New York, NY 10011, USA
/*--*/

/* System library. */

#include <sys_defs.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <stdio.h>          /* strerror() */
#include <errno.h>
#include <netdb.h>
#include <string.h>
#include <htable.h>

/* Utility library. */

#include <msg.h>
#include <mymalloc.h>
#include <stringops.h>
#include <myaddrinfo.h>
#include <sock_addr.h>
#include <inet_proto.h>
#include <split_at.h>

/* Global library. */

#include <mail_proto.h>
#include <valid_mailhost_addr.h>
#include <mail_params.h>
#include <haproxy_srvr.h>

/* Application-specific. */

#include "smtpd.h"

static INET_PROTO_INFO *proto_info;

 /*
  * XXX If we make local port information available via logging, then we must
  * also support these attributes with the XFORWARD command.
  * 
  * XXX If support were to be added for Milter applications in down-stream MTAs,
  * then consistency demands that we propagate a lot of Sendmail macro
  * information via the XFORWARD command. Otherwise we could end up with a
  * very confusing situation.
  */

/* smtpd_peer_sockaddr_to_hostaddr - client address/port to printable form */

static int smtpd_peer_sockaddr_to_hostaddr(SMTPD_STATE *state)
{
    const char *myname = "smtpd_peer_sockaddr_to_hostaddr";
    struct sockaddr *sa = (struct sockaddr *) &(state->sockaddr);
    SOCKADDR_SIZE sa_length = state->sockaddr_len;

    /*
     * XXX If we're given an IPv6 (or IPv4) connection from, e.g., inetd,
     * while Postfix IPv6 (or IPv4) support is turned off, don't (skip to the
     * final else clause, pretend the origin is localhost[127.0.0.1], and
     * become an open relay).
     */
    if (sa->sa_family == AF_INET
#ifdef AF_INET6
    || sa->sa_family == AF_INET6
#endif
    ) {
    MAI_HOSTADDR_STR client_addr;
    MAI_SERVPORT_STR client_port;
    MAI_HOSTADDR_STR server_addr;
    MAI_SERVPORT_STR server_port;
    int     aierr;
    char   *colonp;

    /*
     * Sanity check: we can't use sockets that we're not configured for.
     */
    if (strchr((char *) proto_info->sa_family_list, sa->sa_family) == 0)
        msg_fatal("cannot handle socket type %s with \"%s = %s\"",
#ifdef AF_INET6
              sa->sa_family == AF_INET6 ? "AF_INET6" :
#endif
              sa->sa_family == AF_INET ? "AF_INET" :
              "other", VAR_INET_PROTOCOLS, var_inet_protocols);

    /*
     * Sorry, but there are some things that we just cannot do while
     * connected to the network.
     */
    if (geteuid() != var_owner_uid || getuid() != var_owner_uid) {
        msg_error("incorrect SMTP server privileges: uid=%lu euid=%lu",
              (unsigned long) getuid(), (unsigned long) geteuid());
        msg_fatal("the Postfix SMTP server must run with $%s privileges",
              VAR_MAIL_OWNER);
    }

    /*
     * Convert the client address to printable form.
     */
    if ((aierr = sockaddr_to_hostaddr(sa, sa_length, &client_addr,
                      &client_port, 0)) != 0)
        msg_fatal("%s: cannot convert client address/port to string: %s",
              myname, MAI_STRERROR(aierr));
    state->port = mystrdup(client_port.buf);

    /*
     * XXX Require that the infrastructure strips off the IPv6 datalink
     * suffix to avoid false alarms with strict address syntax checks.
     */
#ifdef HAS_IPV6
    if (strchr(client_addr.buf, '%') != 0)
        msg_panic("%s: address %s has datalink suffix",
              myname, client_addr.buf);
#endif

    /*
     * We convert IPv4-in-IPv6 address to 'true' IPv4 address early on,
     * but only if IPv4 support is enabled (why would anyone want to turn
     * it off)? With IPv4 support enabled we have no need for the IPv6
     * form in logging, hostname verification and access checks.
     */
#ifdef HAS_IPV6
    if (sa->sa_family == AF_INET6) {
        if (strchr((char *) proto_info->sa_family_list, AF_INET) != 0
        && IN6_IS_ADDR_V4MAPPED(&SOCK_ADDR_IN6_ADDR(sa))
        && (colonp = strrchr(client_addr.buf, ':')) != 0) {
        struct addrinfo *res0;

        if (msg_verbose > 1)
            msg_info("%s: rewriting V4-mapped address \"%s\" to \"%s\"",
                 myname, client_addr.buf, colonp + 1);

        state->addr = mystrdup(colonp + 1);
        state->rfc_addr = mystrdup(colonp + 1);
        state->addr_family = AF_INET;
        aierr = hostaddr_to_sockaddr(state->addr, (char *) 0, 0, &res0);
        if (aierr)
            msg_fatal("%s: cannot convert %s from string to binary: %s",
                  myname, state->addr, MAI_STRERROR(aierr));
        sa_length = res0->ai_addrlen;
        if (sa_length > sizeof(state->sockaddr))
            sa_length = sizeof(state->sockaddr);
        memcpy((void *) sa, res0->ai_addr, sa_length);
        freeaddrinfo(res0);     /* 200412 */
        }

        /*
         * Following RFC 2821 section 4.1.3, an IPv6 address literal gets
         * a prefix of 'IPv6:'. We do this consistently for all IPv6
         * addresses that that appear in headers or envelopes. The fact
         * that valid_mailhost_addr() enforces the form helps of course.
         * We use the form without IPV6: prefix when doing access
         * control, or when accessing the connection cache.
         */
        else {
        state->addr = mystrdup(client_addr.buf);
        state->rfc_addr =
            concatenate(IPV6_COL, client_addr.buf, (char *) 0);
        state->addr_family = sa->sa_family;
        }
    }

    /*
     * An IPv4 address is in dotted quad decimal form.
     */
    else
#endif
    {
        state->addr = mystrdup(client_addr.buf);
        state->rfc_addr = mystrdup(client_addr.buf);
        state->addr_family = sa->sa_family;
    }

    /*
     * Convert the server address/port to printable form.
     */
    if ((aierr = sockaddr_to_hostaddr((struct sockaddr *)
                      &state->dest_sockaddr,
                      state->dest_sockaddr_len,
                      &server_addr,
                      &server_port, 0)) != 0)
        msg_fatal("%s: cannot convert server address/port to string: %s",
              myname, MAI_STRERROR(aierr));
    /* TODO: convert IPv4-in-IPv6 to IPv4 form. */
    state->dest_addr = mystrdup(server_addr.buf);
    state->dest_port = mystrdup(server_port.buf);

    return (0);
    }

    /*
     * It's not Internet.
     */
    else {
    return (-1);
    }
}

/* smtpd_peer_sockaddr_to_hostname - client hostname lookup */

static void smtpd_peer_sockaddr_to_hostname(SMTPD_STATE *state)
{
    struct sockaddr *sa = (struct sockaddr *) &(state->sockaddr);
    SOCKADDR_SIZE sa_length = state->sockaddr_len;
    MAI_HOSTNAME_STR client_name;
    int     aierr;

    /*
     * Look up and sanity check the client hostname.
     * 
     * It is unsafe to allow numeric hostnames, especially because there exists
     * pressure to turn off the name->addr double check. In that case an
     * attacker could trivally bypass access restrictions.
     * 
     * sockaddr_to_hostname() already rejects malformed or numeric names.
     */
#define TEMP_AI_ERROR(e) \
    ((e) == EAI_AGAIN || (e) == EAI_MEMORY || (e) == EAI_SYSTEM)

#define REJECT_PEER_NAME(state, code) { \
    myfree(state->name); \
    state->name = mystrdup(CLIENT_NAME_UNKNOWN); \
    state->name_status = code; \
    }

    if (var_smtpd_peername_lookup == 0) {
    state->name = mystrdup(CLIENT_NAME_UNKNOWN);
    state->reverse_name = mystrdup(CLIENT_NAME_UNKNOWN);
    state->name_status = SMTPD_PEER_CODE_PERM;
    state->reverse_name_status = SMTPD_PEER_CODE_PERM;
    } else if ((aierr = sockaddr_to_hostname(sa, sa_length, &client_name,
                     (MAI_SERVNAME_STR *) 0, 0)) != 0) {
    state->name = mystrdup(CLIENT_NAME_UNKNOWN);
    state->reverse_name = mystrdup(CLIENT_NAME_UNKNOWN);
    state->name_status = (TEMP_AI_ERROR(aierr) ?
                  SMTPD_PEER_CODE_TEMP : SMTPD_PEER_CODE_PERM);
    state->reverse_name_status = (TEMP_AI_ERROR(aierr) ?
                   SMTPD_PEER_CODE_TEMP : SMTPD_PEER_CODE_PERM);
    } else {
    struct addrinfo *res0;
    struct addrinfo *res;

    state->name = mystrdup(client_name.buf);
    state->reverse_name = mystrdup(client_name.buf);
    state->name_status = SMTPD_PEER_CODE_OK;
    state->reverse_name_status = SMTPD_PEER_CODE_OK;

    /*
     * Reject the hostname if it does not list the peer address. Without
     * further validation or qualification, such information must not be
     * allowed to enter the audit trail, as people would draw false
     * conclusions.
     */
    aierr = hostname_to_sockaddr_pf(state->name, state->addr_family,
                    (char *) 0, 0, &res0);
    if (aierr) {
        msg_warn("hostname %s does not resolve to address %s: %s",
             state->name, state->addr, MAI_STRERROR(aierr));
        REJECT_PEER_NAME(state, (TEMP_AI_ERROR(aierr) ?
                SMTPD_PEER_CODE_TEMP : SMTPD_PEER_CODE_FORGED));
    } else {
        for (res = res0; /* void */ ; res = res->ai_next) {
        if (res == 0) {
            msg_warn("hostname %s does not resolve to address %s",
                 state->name, state->addr);
            REJECT_PEER_NAME(state, SMTPD_PEER_CODE_FORGED);
            break;
        }
        if (strchr((char *) proto_info->sa_family_list, res->ai_family) == 0) {
            msg_info("skipping address family %d for host %s",
                 res->ai_family, state->name);
            continue;
        }
        if (sock_addr_cmp_addr(res->ai_addr, sa) == 0)
            break;          /* keep peer name */
        }
        freeaddrinfo(res0);
    }
    }
}

/* smtpd_peer_hostaddr_to_sockaddr - convert numeric string to binary */

static void smtpd_peer_hostaddr_to_sockaddr(SMTPD_STATE *state)
{
    const char *myname = "smtpd_peer_hostaddr_to_sockaddr";
    struct addrinfo *res;
    int     aierr;

    if ((aierr = hostaddr_to_sockaddr(state->addr, state->port,
                      SOCK_STREAM, &res)) != 0)
    msg_fatal("%s: cannot convert client address/port to string: %s",
          myname, MAI_STRERROR(aierr));
    if (res->ai_addrlen > sizeof(state->sockaddr))
    msg_panic("%s: address length > struct sockaddr_storage", myname);
    memcpy((void *) &(state->sockaddr), res->ai_addr, res->ai_addrlen);
    state->sockaddr_len = res->ai_addrlen;
    freeaddrinfo(res);
}

/* smtpd_peer_not_inet - non-socket or non-Internet endpoint */

static void smtpd_peer_not_inet(SMTPD_STATE *state)
{

    /*
     * If it's not Internet, assume the client is local, and avoid using the
     * naming service because that can hang when the machine is disconnected.
     */
    state->name = mystrdup("localhost");
    state->reverse_name = mystrdup("localhost");
#ifdef AF_INET6
    if (proto_info->sa_family_list[0] == PF_INET6) {
    state->addr = mystrdup("::1");      /* XXX bogus. */
    state->rfc_addr = mystrdup(IPV6_COL "::1"); /* XXX bogus. */
    } else
#endif
    {
    state->addr = mystrdup("127.0.0.1");    /* XXX bogus. */
    state->rfc_addr = mystrdup("127.0.0.1");/* XXX bogus. */
    }
    state->addr_family = AF_UNSPEC;
    state->name_status = SMTPD_PEER_CODE_OK;
    state->reverse_name_status = SMTPD_PEER_CODE_OK;
    state->port = mystrdup("0");        /* XXX bogus. */

    state->dest_addr = mystrdup(state->addr);   /* XXX bogus. */
    state->dest_port = mystrdup(state->port);   /* XXX bogus. */
}

/* smtpd_peer_no_client - peer went away, or peer info unavailable */

static void smtpd_peer_no_client(SMTPD_STATE *state)
{
    smtpd_peer_reset(state);
    state->name = mystrdup(CLIENT_NAME_UNKNOWN);
    state->reverse_name = mystrdup(CLIENT_NAME_UNKNOWN);
    state->addr = mystrdup(CLIENT_ADDR_UNKNOWN);
    state->rfc_addr = mystrdup(CLIENT_ADDR_UNKNOWN);
    state->addr_family = AF_UNSPEC;
    state->name_status = SMTPD_PEER_CODE_PERM;
    state->reverse_name_status = SMTPD_PEER_CODE_PERM;
    state->port = mystrdup(CLIENT_PORT_UNKNOWN);

    state->dest_addr = mystrdup(SERVER_ADDR_UNKNOWN);
    state->dest_port = mystrdup(SERVER_PORT_UNKNOWN);
}

/* smtpd_peer_from_pass_attr - initialize from attribute hash */

static void smtpd_peer_from_pass_attr(SMTPD_STATE *state)
{
    HTABLE *attr = (HTABLE *) vstream_context(state->client);
    const char *cp;

    /*
     * Extract the client endpoint information from the attribute hash.
     */
    if ((cp = htable_find(attr, MAIL_ATTR_ACT_CLIENT_ADDR)) == 0)
    msg_fatal("missing client address from proxy");
    if (strrchr(cp, ':') != 0) {
    if (valid_ipv6_hostaddr(cp, DO_GRIPE) == 0)
        msg_fatal("bad IPv6 client address syntax from proxy: %s", cp);
    state->addr = mystrdup(cp);
    state->rfc_addr = concatenate(IPV6_COL, cp, (char *) 0);
    state->addr_family = AF_INET6;
    } else {
    if (valid_ipv4_hostaddr(cp, DO_GRIPE) == 0)
        msg_fatal("bad IPv4 client address syntax from proxy: %s", cp);
    state->addr = mystrdup(cp);
    state->rfc_addr = mystrdup(cp);
    state->addr_family = AF_INET;
    }
    if ((cp = htable_find(attr, MAIL_ATTR_ACT_CLIENT_PORT)) == 0)
    msg_fatal("missing client port from proxy");
    if (valid_hostport(cp, DO_GRIPE) == 0)
    msg_fatal("bad TCP client port number syntax from proxy: %s", cp);
    state->port = mystrdup(cp);

    /*
     * The Dovecot authentication server needs the server IP address.
     */
    if ((cp = htable_find(attr, MAIL_ATTR_ACT_SERVER_ADDR)) == 0)
    msg_fatal("missing server address from proxy");
    if (valid_hostaddr(cp, DO_GRIPE) == 0)
    msg_fatal("bad IPv6 server address syntax from proxy: %s", cp);
    state->dest_addr = mystrdup(cp);

    if ((cp = htable_find(attr, MAIL_ATTR_ACT_SERVER_PORT)) == 0)
    msg_fatal("missing server port from proxy");
    if (valid_hostport(cp, DO_GRIPE) == 0)
    msg_fatal("bad TCP server port number syntax from proxy: %s", cp);
    state->dest_port = mystrdup(cp);

    /*
     * Convert the client address from string to binary form.
     */
    smtpd_peer_hostaddr_to_sockaddr(state);
}

/* smtpd_peer_from_default - try to initialize peer information from socket */

static void smtpd_peer_from_default(SMTPD_STATE *state)
{

    /*
     * The "no client" routine provides surrogate information so that the
     * application can produce sensible logging when a client disconnects
     * before the server wakes up. The "not inet" routine provides surrogate
     * state for (presumably) local IPC channels.
     */
    state->sockaddr_len = sizeof(state->sockaddr);
    state->dest_sockaddr_len = sizeof(state->dest_sockaddr);
    if (getpeername(vstream_fileno(state->client),
            (struct sockaddr *) &state->sockaddr,
            &state->sockaddr_len) <0
    || getsockname(vstream_fileno(state->client),
               (struct sockaddr *) &state->dest_sockaddr,
               &state->dest_sockaddr_len) < 0) {
    if (errno == ENOTSOCK)
        smtpd_peer_not_inet(state);
    else
        smtpd_peer_no_client(state);
    } else {
    if (smtpd_peer_sockaddr_to_hostaddr(state) < 0)
        smtpd_peer_not_inet(state);
    }
}

/* smtpd_peer_from_proxy - get endpoint info from proxy agent */

static void smtpd_peer_from_proxy(SMTPD_STATE *state)
{
    typedef struct {
    const char *name;
    int     (*endpt_lookup) (SMTPD_STATE *);
    } SMTPD_ENDPT_LOOKUP_INFO;
    static const SMTPD_ENDPT_LOOKUP_INFO smtpd_endpt_lookup_info[] = {
    HAPROXY_PROTO_NAME, smtpd_peer_from_haproxy,
    0,
    };
    const SMTPD_ENDPT_LOOKUP_INFO *pp;

    /*
     * When the proxy information is unavailable, we can't maintain an audit
     * trail or enforce access control, therefore we forcibly hang up.
     */
    for (pp = smtpd_endpt_lookup_info; /* see below */ ; pp++) {
    if (pp->name == 0)
        msg_fatal("unsupported %s value: %s",
              VAR_SMTPD_UPROXY_PROTO, var_smtpd_uproxy_proto);
    if (strcmp(var_smtpd_uproxy_proto, pp->name) == 0)
        break;
    }
    if (pp->endpt_lookup(state) < 0) {
    smtpd_peer_no_client(state);
    state->flags |= SMTPD_FLAG_HANGUP;
    } else {
    smtpd_peer_hostaddr_to_sockaddr(state);
    }
}

/* smtpd_peer_init - initialize peer information */

void    smtpd_peer_init(SMTPD_STATE *state)
{

    /*
     * Initialize.
     */
    if (proto_info == 0)
    proto_info = inet_proto_info();

    /*
     * Prepare for partial initialization after error.
     */
    memset((void *) &(state->sockaddr), 0, sizeof(state->sockaddr));
    state->sockaddr_len = 0;
    state->name = 0;
    state->reverse_name = 0;
    state->addr = 0;
    state->namaddr = 0;
    state->rfc_addr = 0;
    state->port = 0;
    state->dest_addr = 0;
    state->dest_port = 0;

    /*
     * Determine the remote SMTP client address and port.
     * 
     * XXX In stand-alone mode, don't assume that the peer will be a local
     * process. That could introduce a gaping hole when the SMTP daemon is
     * hooked up to the network via inetd or some other super-server.
     */
    if (vstream_context(state->client) != 0) {
    smtpd_peer_from_pass_attr(state);
    if (*var_smtpd_uproxy_proto != 0)
        msg_warn("ignoring non-empty %s setting behind postscreen",
             VAR_SMTPD_UPROXY_PROTO);
    } else if (SMTPD_STAND_ALONE(state) || *var_smtpd_uproxy_proto == 0) {
    smtpd_peer_from_default(state);
    } else {
    smtpd_peer_from_proxy(state);
    }

    /*
     * Determine the remote SMTP client hostname. Note: some of the handlers
     * above provide surrogate endpoint information in case of error. In that
     * case, leave the surrogate information alone.
     */
    if (state->name == 0)
    smtpd_peer_sockaddr_to_hostname(state);

    /*
     * Do the name[addr]:port formatting for pretty reports.
     */
    state->namaddr = SMTPD_BUILD_NAMADDRPORT(state->name, state->addr,
                         state->port);
}

/* smtpd_peer_reset - destroy peer information */

void    smtpd_peer_reset(SMTPD_STATE *state)
{
    if (state->name)
    myfree(state->name);
    if (state->reverse_name)
    myfree(state->reverse_name);
    if (state->addr)
    myfree(state->addr);
    if (state->namaddr)
    myfree(state->namaddr);
    if (state->rfc_addr)
    myfree(state->rfc_addr);
    if (state->port)
    myfree(state->port);
    if (state->dest_addr)
    myfree(state->dest_addr);
    if (state->dest_port)
    myfree(state->dest_port);
}