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view src/mail/ngx_mail_proxy_module.c @ 7839:3974f4e56a4e

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Mail: fixed s->arg_start clearing on invalid IMAP commands. Previously, s->arg_start was left intact after invalid IMAP commands, and this might result in an argument incorrectly added to the following command. Similarly, s->backslash was left intact as well, leading to unneeded backslash removal. For example (LFs from the client are explicitly shown as "<LF>"): S: * OK IMAP4 ready C: a01 login "\<LF> S: a01 BAD invalid command C: a0000000000\2 authenticate <LF> S: a00000000002 aBAD invalid command The backslash followed by LF generates invalid command with s->arg_start and s->backslash set, the following command incorrectly treats anything from the old s->arg_start to the space after the command as an argument, and removes the backslash from the tag. If there is no space, s->arg_end will be NULL. Both things seem to be harmless though. In particular: - This can be used to provide an incorrect argument to a command without arguments. The only command which seems to look at the single argument is AUTHENTICATE, and it checks the argument length before trying to access it. - Backslash removal uses the "end" pointer, and stops due to "src < end" condition instead of scanning all the process memory if s->arg_end is NULL (and arg[0].len is huge). - There should be no backslashes in unquoted strings. An obvious fix is to clear s->arg_start and s->backslash on invalid commands, similarly to how it is done in POP3 parsing (added in 810:e3aa8f305d21) and SMTP parsing. This, however, makes it clear that s->arg_start handling in the "done" label is wrong: s->arg_start cannot be legitimately set there, as it is expected to be cleared in all possible cases when the "done" label is reached. The relevant code is dead and will be removed by the following change.
author Maxim Dounin <mdounin@mdounin.ru>
date Wed, 19 May 2021 03:13:20 +0300
parents 815c63581be4
children b38728495e1a
line wrap: on
line source


/*
 * Copyright (C) Igor Sysoev
 * Copyright (C) Nginx, Inc.
 */


#include <ngx_config.h>
#include <ngx_core.h>
#include <ngx_event.h>
#include <ngx_event_connect.h>
#include <ngx_mail.h>


typedef struct {
    ngx_flag_t  enable;
    ngx_flag_t  pass_error_message;
    ngx_flag_t  xclient;
    ngx_flag_t  smtp_auth;
    ngx_flag_t  proxy_protocol;
    size_t      buffer_size;
    ngx_msec_t  timeout;
} ngx_mail_proxy_conf_t;


static void ngx_mail_proxy_block_read(ngx_event_t *rev);
static void ngx_mail_proxy_pop3_handler(ngx_event_t *rev);
static void ngx_mail_proxy_imap_handler(ngx_event_t *rev);
static void ngx_mail_proxy_smtp_handler(ngx_event_t *rev);
static void ngx_mail_proxy_write_handler(ngx_event_t *wev);
static ngx_int_t ngx_mail_proxy_send_proxy_protocol(ngx_mail_session_t *s);
static ngx_int_t ngx_mail_proxy_read_response(ngx_mail_session_t *s,
    ngx_uint_t state);
static void ngx_mail_proxy_handler(ngx_event_t *ev);
static void ngx_mail_proxy_upstream_error(ngx_mail_session_t *s);
static void ngx_mail_proxy_internal_server_error(ngx_mail_session_t *s);
static void ngx_mail_proxy_close_session(ngx_mail_session_t *s);
static void *ngx_mail_proxy_create_conf(ngx_conf_t *cf);
static char *ngx_mail_proxy_merge_conf(ngx_conf_t *cf, void *parent,
    void *child);


static ngx_command_t  ngx_mail_proxy_commands[] = {

    { ngx_string("proxy"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_FLAG,
      ngx_conf_set_flag_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_proxy_conf_t, enable),
      NULL },

    { ngx_string("proxy_buffer"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_size_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_proxy_conf_t, buffer_size),
      NULL },

    { ngx_string("proxy_timeout"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_TAKE1,
      ngx_conf_set_msec_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_proxy_conf_t, timeout),
      NULL },

    { ngx_string("proxy_pass_error_message"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_FLAG,
      ngx_conf_set_flag_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_proxy_conf_t, pass_error_message),
      NULL },

    { ngx_string("xclient"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_FLAG,
      ngx_conf_set_flag_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_proxy_conf_t, xclient),
      NULL },

    { ngx_string("proxy_smtp_auth"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_FLAG,
      ngx_conf_set_flag_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_proxy_conf_t, smtp_auth),
      NULL },

    { ngx_string("proxy_protocol"),
      NGX_MAIL_MAIN_CONF|NGX_MAIL_SRV_CONF|NGX_CONF_FLAG,
      ngx_conf_set_flag_slot,
      NGX_MAIL_SRV_CONF_OFFSET,
      offsetof(ngx_mail_proxy_conf_t, proxy_protocol),
      NULL },

      ngx_null_command
};


static ngx_mail_module_t  ngx_mail_proxy_module_ctx = {
    NULL,                                  /* protocol */

    NULL,                                  /* create main configuration */
    NULL,                                  /* init main configuration */

    ngx_mail_proxy_create_conf,            /* create server configuration */
    ngx_mail_proxy_merge_conf              /* merge server configuration */
};


ngx_module_t  ngx_mail_proxy_module = {
    NGX_MODULE_V1,
    &ngx_mail_proxy_module_ctx,            /* module context */
    ngx_mail_proxy_commands,               /* module directives */
    NGX_MAIL_MODULE,                       /* module type */
    NULL,                                  /* init master */
    NULL,                                  /* init module */
    NULL,                                  /* init process */
    NULL,                                  /* init thread */
    NULL,                                  /* exit thread */
    NULL,                                  /* exit process */
    NULL,                                  /* exit master */
    NGX_MODULE_V1_PADDING
};


static u_char  smtp_auth_ok[] = "235 2.0.0 OK" CRLF;


void
ngx_mail_proxy_init(ngx_mail_session_t *s, ngx_addr_t *peer)
{
    ngx_int_t                  rc;
    ngx_mail_proxy_ctx_t      *p;
    ngx_mail_proxy_conf_t     *pcf;
    ngx_mail_core_srv_conf_t  *cscf;

    s->connection->log->action = "connecting to upstream";

    cscf = ngx_mail_get_module_srv_conf(s, ngx_mail_core_module);

    p = ngx_pcalloc(s->connection->pool, sizeof(ngx_mail_proxy_ctx_t));
    if (p == NULL) {
        ngx_mail_session_internal_server_error(s);
        return;
    }

    s->proxy = p;

    p->upstream.sockaddr = peer->sockaddr;
    p->upstream.socklen = peer->socklen;
    p->upstream.name = &peer->name;
    p->upstream.get = ngx_event_get_peer;
    p->upstream.log = s->connection->log;
    p->upstream.log_error = NGX_ERROR_ERR;

    rc = ngx_event_connect_peer(&p->upstream);

    if (rc == NGX_ERROR || rc == NGX_BUSY || rc == NGX_DECLINED) {
        ngx_mail_proxy_internal_server_error(s);
        return;
    }

    ngx_add_timer(p->upstream.connection->read, cscf->timeout);

    p->upstream.connection->data = s;
    p->upstream.connection->pool = s->connection->pool;

    s->connection->read->handler = ngx_mail_proxy_block_read;
    p->upstream.connection->write->handler = ngx_mail_proxy_write_handler;

    pcf = ngx_mail_get_module_srv_conf(s, ngx_mail_proxy_module);

    s->proxy->buffer = ngx_create_temp_buf(s->connection->pool,
                                           pcf->buffer_size);
    if (s->proxy->buffer == NULL) {
        ngx_mail_proxy_internal_server_error(s);
        return;
    }

    s->proxy->proxy_protocol = pcf->proxy_protocol;

    s->out.len = 0;

    switch (s->protocol) {

    case NGX_MAIL_POP3_PROTOCOL:
        p->upstream.connection->read->handler = ngx_mail_proxy_pop3_handler;
        s->mail_state = ngx_pop3_start;
        break;

    case NGX_MAIL_IMAP_PROTOCOL:
        p->upstream.connection->read->handler = ngx_mail_proxy_imap_handler;
        s->mail_state = ngx_imap_start;
        break;

    default: /* NGX_MAIL_SMTP_PROTOCOL */
        p->upstream.connection->read->handler = ngx_mail_proxy_smtp_handler;
        s->mail_state = ngx_smtp_start;
        break;
    }

    if (rc == NGX_AGAIN) {
        return;
    }

    ngx_mail_proxy_write_handler(p->upstream.connection->write);
}


static void
ngx_mail_proxy_block_read(ngx_event_t *rev)
{
    ngx_connection_t    *c;
    ngx_mail_session_t  *s;

    ngx_log_debug0(NGX_LOG_DEBUG_MAIL, rev->log, 0, "mail proxy block read");

    if (ngx_handle_read_event(rev, 0) != NGX_OK) {
        c = rev->data;
        s = c->data;

        ngx_mail_proxy_close_session(s);
    }
}


static void
ngx_mail_proxy_pop3_handler(ngx_event_t *rev)
{
    u_char                 *p;
    ngx_int_t               rc;
    ngx_str_t               line;
    ngx_connection_t       *c;
    ngx_mail_session_t     *s;
    ngx_mail_proxy_conf_t  *pcf;

    ngx_log_debug0(NGX_LOG_DEBUG_MAIL, rev->log, 0,
                   "mail proxy pop3 auth handler");

    c = rev->data;
    s = c->data;

    if (rev->timedout) {
        ngx_log_error(NGX_LOG_INFO, c->log, NGX_ETIMEDOUT,
                      "upstream timed out");
        c->timedout = 1;
        ngx_mail_proxy_internal_server_error(s);
        return;
    }

    if (s->proxy->proxy_protocol) {
        ngx_log_debug0(NGX_LOG_DEBUG_MAIL, c->log, 0, "mail proxy pop3 busy");

        if (ngx_handle_read_event(c->read, 0) != NGX_OK) {
            ngx_mail_proxy_internal_server_error(s);
            return;
        }

        return;
    }

    rc = ngx_mail_proxy_read_response(s, 0);

    if (rc == NGX_AGAIN) {
        if (ngx_handle_read_event(c->read, 0) != NGX_OK) {
            ngx_mail_proxy_internal_server_error(s);
            return;
        }

        return;
    }

    if (rc == NGX_ERROR) {
        ngx_mail_proxy_upstream_error(s);
        return;
    }

    switch (s->mail_state) {

    case ngx_pop3_start:
        ngx_log_debug0(NGX_LOG_DEBUG_MAIL, rev->log, 0, "mail proxy send user");

        s->connection->log->action = "sending user name to upstream";

        line.len = sizeof("USER ")  - 1 + s->login.len + 2;
        line.data = ngx_pnalloc(c->pool, line.len);
        if (line.data == NULL) {
            ngx_mail_proxy_internal_server_error(s);
            return;
        }

        p = ngx_cpymem(line.data, "USER ", sizeof("USER ") - 1);
        p = ngx_cpymem(p, s->login.data, s->login.len);
        *p++ = CR; *p = LF;

        s->mail_state = ngx_pop3_user;
        break;

    case ngx_pop3_user:
        ngx_log_debug0(NGX_LOG_DEBUG_MAIL, rev->log, 0, "mail proxy send pass");

        s->connection->log->action = "sending password to upstream";

        line.len = sizeof("PASS ")  - 1 + s->passwd.len + 2;
        line.data = ngx_pnalloc(c->pool, line.len);
        if (line.data == NULL) {
            ngx_mail_proxy_internal_server_error(s);
            return;
        }

        p = ngx_cpymem(line.data, "PASS ", sizeof("PASS ") - 1);
        p = ngx_cpymem(p, s->passwd.data, s->passwd.len);
        *p++ = CR; *p = LF;

        s->mail_state = ngx_pop3_passwd;
        break;

    case ngx_pop3_passwd:
        s->connection->read->handler = ngx_mail_proxy_handler;
        s->connection->write->handler = ngx_mail_proxy_handler;
        rev->handler = ngx_mail_proxy_handler;
        c->write->handler = ngx_mail_proxy_handler;

        pcf = ngx_mail_get_module_srv_conf(s, ngx_mail_proxy_module);
        ngx_add_timer(s->connection->read, pcf->timeout);
        ngx_del_timer(c->read);

        c->log->action = NULL;
        ngx_log_error(NGX_LOG_INFO, c->log, 0, "client logged in");

        if (s->buffer->pos < s->buffer->last) {
            ngx_post_event(c->write, &ngx_posted_events);
        }

        ngx_mail_proxy_handler(s->connection->write);

        return;

    default:
#if (NGX_SUPPRESS_WARN)
        ngx_str_null(&line);
#endif
        break;
    }

    if (c->send(c, line.data, line.len) < (ssize_t) line.len) {
        /*
         * we treat the incomplete sending as NGX_ERROR
         * because it is very strange here
         */
        ngx_mail_proxy_internal_server_error(s);
        return;
    }

    if (ngx_handle_read_event(c->read, 0) != NGX_OK) {
        ngx_mail_proxy_internal_server_error(s);
        return;
    }

    s->proxy->buffer->pos = s->proxy->buffer->start;
    s->proxy->buffer->last = s->proxy->buffer->start;
}


static void
ngx_mail_proxy_imap_handler(ngx_event_t *rev)
{
    u_char                 *p;
    ngx_int_t               rc;
    ngx_str_t               line;
    ngx_connection_t       *c;
    ngx_mail_session_t     *s;
    ngx_mail_proxy_conf_t  *pcf;

    ngx_log_debug0(NGX_LOG_DEBUG_MAIL, rev->log, 0,
                   "mail proxy imap auth handler");

    c = rev->data;
    s = c->data;

    if (rev->timedout) {
        ngx_log_error(NGX_LOG_INFO, c->log, NGX_ETIMEDOUT,
                      "upstream timed out");
        c->timedout = 1;
        ngx_mail_proxy_internal_server_error(s);
        return;
    }

    if (s->proxy->proxy_protocol) {
        ngx_log_debug0(NGX_LOG_DEBUG_MAIL, c->log, 0, "mail proxy imap busy");

        if (ngx_handle_read_event(c->read, 0) != NGX_OK) {
            ngx_mail_proxy_internal_server_error(s);
            return;
        }

        return;
    }

    rc = ngx_mail_proxy_read_response(s, s->mail_state);

    if (rc == NGX_AGAIN) {
        if (ngx_handle_read_event(c->read, 0) != NGX_OK) {
            ngx_mail_proxy_internal_server_error(s);
            return;
        }

        return;
    }

    if (rc == NGX_ERROR) {
        ngx_mail_proxy_upstream_error(s);
        return;
    }

    switch (s->mail_state) {

    case ngx_imap_start:
        ngx_log_debug0(NGX_LOG_DEBUG_MAIL, rev->log, 0,
                       "mail proxy send login");

        s->connection->log->action = "sending LOGIN command to upstream";

        line.len = s->tag.len + sizeof("LOGIN ") - 1
                   + 1 + NGX_SIZE_T_LEN + 1 + 2;
        line.data = ngx_pnalloc(c->pool, line.len);
        if (line.data == NULL) {
            ngx_mail_proxy_internal_server_error(s);
            return;
        }

        line.len = ngx_sprintf(line.data, "%VLOGIN {%uz}" CRLF,
                               &s->tag, s->login.len)
                   - line.data;

        s->mail_state = ngx_imap_login;
        break;

    case ngx_imap_login:
        ngx_log_debug0(NGX_LOG_DEBUG_MAIL, rev->log, 0, "mail proxy send user");

        s->connection->log->action = "sending user name to upstream";

        line.len = s->login.len + 1 + 1 + NGX_SIZE_T_LEN + 1 + 2;
        line.data = ngx_pnalloc(c->pool, line.len);
        if (line.data == NULL) {
            ngx_mail_proxy_internal_server_error(s);
            return;
        }

        line.len = ngx_sprintf(line.data, "%V {%uz}" CRLF,
                               &s->login, s->passwd.len)
                   - line.data;

        s->mail_state = ngx_imap_user;
        break;

    case ngx_imap_user:
        ngx_log_debug0(NGX_LOG_DEBUG_MAIL, rev->log, 0,
                       "mail proxy send passwd");

        s->connection->log->action = "sending password to upstream";

        line.len = s->passwd.len + 2;
        line.data = ngx_pnalloc(c->pool, line.len);
        if (line.data == NULL) {
            ngx_mail_proxy_internal_server_error(s);
            return;
        }

        p = ngx_cpymem(line.data, s->passwd.data, s->passwd.len);
        *p++ = CR; *p = LF;

        s->mail_state = ngx_imap_passwd;
        break;

    case ngx_imap_passwd:
        s->connection->read->handler = ngx_mail_proxy_handler;
        s->connection->write->handler = ngx_mail_proxy_handler;
        rev->handler = ngx_mail_proxy_handler;
        c->write->handler = ngx_mail_proxy_handler;

        pcf = ngx_mail_get_module_srv_conf(s, ngx_mail_proxy_module);
        ngx_add_timer(s->connection->read, pcf->timeout);
        ngx_del_timer(c->read);

        c->log->action = NULL;
        ngx_log_error(NGX_LOG_INFO, c->log, 0, "client logged in");

        ngx_mail_proxy_handler(s->connection->write);

        return;

    default:
#if (NGX_SUPPRESS_WARN)
        ngx_str_null(&line);
#endif
        break;
    }

    if (c->send(c, line.data, line.len) < (ssize_t) line.len) {
        /*
         * we treat the incomplete sending as NGX_ERROR
         * because it is very strange here
         */
        ngx_mail_proxy_internal_server_error(s);
        return;
    }

    if (ngx_handle_read_event(c->read, 0) != NGX_OK) {
        ngx_mail_proxy_internal_server_error(s);
        return;
    }

    s->proxy->buffer->pos = s->proxy->buffer->start;
    s->proxy->buffer->last = s->proxy->buffer->start;
}


static void
ngx_mail_proxy_smtp_handler(ngx_event_t *rev)
{
    u_char                    *p;
    ngx_int_t                  rc;
    ngx_str_t                  line, auth, encoded;
    ngx_buf_t                 *b;
    ngx_connection_t          *c;
    ngx_mail_session_t        *s;
    ngx_mail_proxy_conf_t     *pcf;
    ngx_mail_core_srv_conf_t  *cscf;

    ngx_log_debug0(NGX_LOG_DEBUG_MAIL, rev->log, 0,
                   "mail proxy smtp auth handler");

    c = rev->data;
    s = c->data;

    if (rev->timedout) {
        ngx_log_error(NGX_LOG_INFO, c->log, NGX_ETIMEDOUT,
                      "upstream timed out");
        c->timedout = 1;
        ngx_mail_proxy_internal_server_error(s);
        return;
    }

    if (s->proxy->proxy_protocol) {
        ngx_log_debug0(NGX_LOG_DEBUG_MAIL, c->log, 0, "mail proxy smtp busy");

        if (ngx_handle_read_event(c->read, 0) != NGX_OK) {
            ngx_mail_proxy_internal_server_error(s);
            return;
        }

        return;
    }

    rc = ngx_mail_proxy_read_response(s, s->mail_state);

    if (rc == NGX_AGAIN) {
        if (ngx_handle_read_event(c->read, 0) != NGX_OK) {
            ngx_mail_proxy_internal_server_error(s);
            return;
        }

        return;
    }

    if (rc == NGX_ERROR) {
        ngx_mail_proxy_upstream_error(s);
        return;
    }

    switch (s->mail_state) {

    case ngx_smtp_start:
        ngx_log_debug0(NGX_LOG_DEBUG_MAIL, rev->log, 0, "mail proxy send ehlo");

        s->connection->log->action = "sending HELO/EHLO to upstream";

        cscf = ngx_mail_get_module_srv_conf(s, ngx_mail_core_module);

        line.len = sizeof("HELO ")  - 1 + cscf->server_name.len + 2;
        line.data = ngx_pnalloc(c->pool, line.len);
        if (line.data == NULL) {
            ngx_mail_proxy_internal_server_error(s);
            return;
        }

        pcf = ngx_mail_get_module_srv_conf(s, ngx_mail_proxy_module);

        p = ngx_cpymem(line.data,
                       ((s->esmtp || pcf->xclient) ? "EHLO " : "HELO "),
                       sizeof("HELO ") - 1);

        p = ngx_cpymem(p, cscf->server_name.data, cscf->server_name.len);
        *p++ = CR; *p = LF;

        if (pcf->xclient) {
            s->mail_state = ngx_smtp_helo_xclient;

        } else if (s->auth_method == NGX_MAIL_AUTH_NONE) {
            s->mail_state = ngx_smtp_helo_from;

        } else if (pcf->smtp_auth) {
            s->mail_state = ngx_smtp_helo_auth;

        } else {
            s->mail_state = ngx_smtp_helo;
        }

        break;

    case ngx_smtp_helo_xclient:
        ngx_log_debug0(NGX_LOG_DEBUG_MAIL, rev->log, 0,
                       "mail proxy send xclient");

        s->connection->log->action = "sending XCLIENT to upstream";

        line.len = sizeof("XCLIENT ADDR= LOGIN= NAME="
                          CRLF) - 1
                   + s->connection->addr_text.len + s->login.len + s->host.len;

#if (NGX_HAVE_INET6)
        if (s->connection->sockaddr->sa_family == AF_INET6) {
            line.len += sizeof("IPV6:") - 1;
        }
#endif

        line.data = ngx_pnalloc(c->pool, line.len);
        if (line.data == NULL) {
            ngx_mail_proxy_internal_server_error(s);
            return;
        }

        p = ngx_cpymem(line.data, "XCLIENT ADDR=", sizeof("XCLIENT ADDR=") - 1);

#if (NGX_HAVE_INET6)
        if (s->connection->sockaddr->sa_family == AF_INET6) {
            p = ngx_cpymem(p, "IPV6:", sizeof("IPV6:") - 1);
        }
#endif

        p = ngx_copy(p, s->connection->addr_text.data,
                     s->connection->addr_text.len);

        pcf = ngx_mail_get_module_srv_conf(s, ngx_mail_proxy_module);

        if (s->login.len && !pcf->smtp_auth) {
            p = ngx_cpymem(p, " LOGIN=", sizeof(" LOGIN=") - 1);
            p = ngx_copy(p, s->login.data, s->login.len);
        }

        p = ngx_cpymem(p, " NAME=", sizeof(" NAME=") - 1);
        p = ngx_copy(p, s->host.data, s->host.len);

        *p++ = CR; *p++ = LF;

        line.len = p - line.data;

        if (s->smtp_helo.len) {
            s->mail_state = ngx_smtp_xclient_helo;

        } else if (s->auth_method == NGX_MAIL_AUTH_NONE) {
            s->mail_state = ngx_smtp_xclient_from;

        } else if (pcf->smtp_auth) {
            s->mail_state = ngx_smtp_xclient_auth;

        } else {
            s->mail_state = ngx_smtp_xclient;
        }

        break;

    case ngx_smtp_xclient_helo:
        ngx_log_debug0(NGX_LOG_DEBUG_MAIL, rev->log, 0,
                       "mail proxy send client ehlo");

        s->connection->log->action = "sending client HELO/EHLO to upstream";

        line.len = sizeof("HELO " CRLF) - 1 + s->smtp_helo.len;

        line.data = ngx_pnalloc(c->pool, line.len);
        if (line.data == NULL) {
            ngx_mail_proxy_internal_server_error(s);
            return;
        }

        line.len = ngx_sprintf(line.data,
                       ((s->esmtp) ? "EHLO %V" CRLF : "HELO %V" CRLF),
                       &s->smtp_helo)
                   - line.data;

        pcf = ngx_mail_get_module_srv_conf(s, ngx_mail_proxy_module);

        if (s->auth_method == NGX_MAIL_AUTH_NONE) {
            s->mail_state = ngx_smtp_helo_from;

        } else if (pcf->smtp_auth) {
            s->mail_state = ngx_smtp_helo_auth;

        } else {
            s->mail_state = ngx_smtp_helo;
        }

        break;

    case ngx_smtp_helo_auth:
    case ngx_smtp_xclient_auth:
        ngx_log_debug0(NGX_LOG_DEBUG_MAIL, rev->log, 0,
                       "mail proxy send auth");

        s->connection->log->action = "sending AUTH to upstream";

        if (s->passwd.data == NULL) {
            ngx_log_error(NGX_LOG_ERR, s->connection->log, 0,
                          "no password available");
            ngx_mail_proxy_internal_server_error(s);
            return;
        }

        auth.len = 1 + s->login.len + 1 + s->passwd.len;
        auth.data = ngx_pnalloc(c->pool, auth.len);
        if (auth.data == NULL) {
            ngx_mail_proxy_internal_server_error(s);
            return;
        }

        auth.len = ngx_sprintf(auth.data, "%Z%V%Z%V", &s->login, &s->passwd)
                   - auth.data;

        line.len = sizeof("AUTH PLAIN " CRLF) - 1
                   + ngx_base64_encoded_length(auth.len);

        line.data = ngx_pnalloc(c->pool, line.len);
        if (line.data == NULL) {
            ngx_mail_proxy_internal_server_error(s);
            return;
        }

        encoded.data = ngx_cpymem(line.data, "AUTH PLAIN ",
                                  sizeof("AUTH PLAIN ") - 1);

        ngx_encode_base64(&encoded, &auth);

        p = encoded.data + encoded.len;
        *p++ = CR; *p = LF;

        s->mail_state = ngx_smtp_auth_plain;

        break;

    case ngx_smtp_helo_from:
    case ngx_smtp_xclient_from:
        ngx_log_debug0(NGX_LOG_DEBUG_MAIL, rev->log, 0,
                       "mail proxy send mail from");

        s->connection->log->action = "sending MAIL FROM to upstream";

        line.len = s->smtp_from.len + sizeof(CRLF) - 1;
        line.data = ngx_pnalloc(c->pool, line.len);
        if (line.data == NULL) {
            ngx_mail_proxy_internal_server_error(s);
            return;
        }

        p = ngx_cpymem(line.data, s->smtp_from.data, s->smtp_from.len);
        *p++ = CR; *p = LF;

        s->mail_state = ngx_smtp_from;

        break;

    case ngx_smtp_from:
        ngx_log_debug0(NGX_LOG_DEBUG_MAIL, rev->log, 0,
                       "mail proxy send rcpt to");

        s->connection->log->action = "sending RCPT TO to upstream";

        line.len = s->smtp_to.len + sizeof(CRLF) - 1;
        line.data = ngx_pnalloc(c->pool, line.len);
        if (line.data == NULL) {
            ngx_mail_proxy_internal_server_error(s);
            return;
        }

        p = ngx_cpymem(line.data, s->smtp_to.data, s->smtp_to.len);
        *p++ = CR; *p = LF;

        s->mail_state = ngx_smtp_to;

        break;

    case ngx_smtp_helo:
    case ngx_smtp_xclient:
    case ngx_smtp_auth_plain:
    case ngx_smtp_to:

        b = s->proxy->buffer;

        if (s->auth_method == NGX_MAIL_AUTH_NONE) {
            b->pos = b->start;

        } else {
            ngx_memcpy(b->start, smtp_auth_ok, sizeof(smtp_auth_ok) - 1);
            b->last = b->start + sizeof(smtp_auth_ok) - 1;
        }

        s->connection->read->handler = ngx_mail_proxy_handler;
        s->connection->write->handler = ngx_mail_proxy_handler;
        rev->handler = ngx_mail_proxy_handler;
        c->write->handler = ngx_mail_proxy_handler;

        pcf = ngx_mail_get_module_srv_conf(s, ngx_mail_proxy_module);
        ngx_add_timer(s->connection->read, pcf->timeout);
        ngx_del_timer(c->read);

        c->log->action = NULL;
        ngx_log_error(NGX_LOG_INFO, c->log, 0, "client logged in");

        if (s->buffer->pos < s->buffer->last) {
            ngx_post_event(c->write, &ngx_posted_events);
        }

        ngx_mail_proxy_handler(s->connection->write);

        return;

    default:
#if (NGX_SUPPRESS_WARN)
        ngx_str_null(&line);
#endif
        break;
    }

    if (c->send(c, line.data, line.len) < (ssize_t) line.len) {
        /*
         * we treat the incomplete sending as NGX_ERROR
         * because it is very strange here
         */
        ngx_mail_proxy_internal_server_error(s);
        return;
    }

    if (ngx_handle_read_event(c->read, 0) != NGX_OK) {
        ngx_mail_proxy_internal_server_error(s);
        return;
    }

    s->proxy->buffer->pos = s->proxy->buffer->start;
    s->proxy->buffer->last = s->proxy->buffer->start;
}


static void
ngx_mail_proxy_write_handler(ngx_event_t *wev)
{
    ngx_connection_t    *c;
    ngx_mail_session_t  *s;

    ngx_log_debug0(NGX_LOG_DEBUG_MAIL, wev->log, 0, "mail proxy write handler");

    c = wev->data;
    s = c->data;

    if (s->proxy->proxy_protocol) {
        if (ngx_mail_proxy_send_proxy_protocol(s) != NGX_OK) {
            return;
        }

        s->proxy->proxy_protocol = 0;
    }

    if (ngx_handle_write_event(wev, 0) != NGX_OK) {
        ngx_mail_proxy_internal_server_error(s);
    }

    if (c->read->ready) {
        ngx_post_event(c->read, &ngx_posted_events);
    }
}


static ngx_int_t
ngx_mail_proxy_send_proxy_protocol(ngx_mail_session_t *s)
{
    u_char            *p;
    ssize_t            n, size;
    ngx_connection_t  *c;
    u_char             buf[NGX_PROXY_PROTOCOL_MAX_HEADER];

    s->connection->log->action = "sending PROXY protocol header to upstream";

    ngx_log_debug0(NGX_LOG_DEBUG_MAIL, s->connection->log, 0,
                   "mail proxy send PROXY protocol header");

    p = ngx_proxy_protocol_write(s->connection, buf,
                                 buf + NGX_PROXY_PROTOCOL_MAX_HEADER);
    if (p == NULL) {
        ngx_mail_proxy_internal_server_error(s);
        return NGX_ERROR;
    }

    c = s->proxy->upstream.connection;

    size = p - buf;

    n = c->send(c, buf, size);

    if (n == NGX_AGAIN) {
        if (ngx_handle_write_event(c->write, 0) != NGX_OK) {
            ngx_mail_proxy_internal_server_error(s);
            return NGX_ERROR;
        }

        return NGX_AGAIN;
    }

    if (n == NGX_ERROR) {
        ngx_mail_proxy_internal_server_error(s);
        return NGX_ERROR;
    }

    if (n != size) {

        /*
         * PROXY protocol specification:
         * The sender must always ensure that the header
         * is sent at once, so that the transport layer
         * maintains atomicity along the path to the receiver.
         */

        ngx_log_error(NGX_LOG_ERR, s->connection->log, 0,
                      "could not send PROXY protocol header at once");

        ngx_mail_proxy_internal_server_error(s);

        return NGX_ERROR;
    }

    return NGX_OK;
}


static ngx_int_t
ngx_mail_proxy_read_response(ngx_mail_session_t *s, ngx_uint_t state)
{
    u_char                 *p, *m;
    ssize_t                 n;
    ngx_buf_t              *b;
    ngx_mail_proxy_conf_t  *pcf;

    s->connection->log->action = "reading response from upstream";

    b = s->proxy->buffer;

    n = s->proxy->upstream.connection->recv(s->proxy->upstream.connection,
                                            b->last, b->end - b->last);

    if (n == NGX_ERROR || n == 0) {
        return NGX_ERROR;
    }

    if (n == NGX_AGAIN) {
        return NGX_AGAIN;
    }

    b->last += n;

    if (b->last - b->pos < 4) {
        return NGX_AGAIN;
    }

    if (*(b->last - 2) != CR || *(b->last - 1) != LF) {
        if (b->last == b->end) {
            *(b->last - 1) = '\0';
            ngx_log_error(NGX_LOG_ERR, s->connection->log, 0,
                          "upstream sent too long response line: \"%s\"",
                          b->pos);
            return NGX_ERROR;
        }

        return NGX_AGAIN;
    }

    p = b->pos;

    switch (s->protocol) {

    case NGX_MAIL_POP3_PROTOCOL:
        if (p[0] == '+' && p[1] == 'O' && p[2] == 'K') {
            return NGX_OK;
        }
        break;

    case NGX_MAIL_IMAP_PROTOCOL:
        switch (state) {

        case ngx_imap_start:
            if (p[0] == '*' && p[1] == ' ' && p[2] == 'O' && p[3] == 'K') {
                return NGX_OK;
            }
            break;

        case ngx_imap_login:
        case ngx_imap_user:
            if (p[0] == '+') {
                return NGX_OK;
            }
            break;

        case ngx_imap_passwd:
            if (ngx_strncmp(p, s->tag.data, s->tag.len) == 0) {
                p += s->tag.len;
                if (p[0] == 'O' && p[1] == 'K') {
                    return NGX_OK;
                }
            }
            break;
        }

        break;

    default: /* NGX_MAIL_SMTP_PROTOCOL */

        if (p[3] == '-') {
            /* multiline reply, check if we got last line */

            m = b->last - (sizeof(CRLF "200" CRLF) - 1);

            while (m > p) {
                if (m[0] == CR && m[1] == LF) {
                    break;
                }

                m--;
            }

            if (m <= p || m[5] == '-') {
                return NGX_AGAIN;
            }
        }

        switch (state) {

        case ngx_smtp_start:
            if (p[0] == '2' && p[1] == '2' && p[2] == '0') {
                return NGX_OK;
            }
            break;

        case ngx_smtp_helo:
        case ngx_smtp_helo_xclient:
        case ngx_smtp_helo_from:
        case ngx_smtp_helo_auth:
        case ngx_smtp_from:
            if (p[0] == '2' && p[1] == '5' && p[2] == '0') {
                return NGX_OK;
            }
            break;

        case ngx_smtp_xclient:
        case ngx_smtp_xclient_from:
        case ngx_smtp_xclient_helo:
        case ngx_smtp_xclient_auth:
            if (p[0] == '2' && (p[1] == '2' || p[1] == '5') && p[2] == '0') {
                return NGX_OK;
            }
            break;

        case ngx_smtp_auth_plain:
            if (p[0] == '2' && p[1] == '3' && p[2] == '5') {
                return NGX_OK;
            }
            break;

        case ngx_smtp_to:
            return NGX_OK;
        }

        break;
    }

    pcf = ngx_mail_get_module_srv_conf(s, ngx_mail_proxy_module);

    if (pcf->pass_error_message == 0) {
        *(b->last - 2) = '\0';
        ngx_log_error(NGX_LOG_ERR, s->connection->log, 0,
                      "upstream sent invalid response: \"%s\"", p);
        return NGX_ERROR;
    }

    s->out.len = b->last - p - 2;
    s->out.data = p;

    ngx_log_error(NGX_LOG_INFO, s->connection->log, 0,
                  "upstream sent invalid response: \"%V\"", &s->out);

    s->out.len = b->last - b->pos;
    s->out.data = b->pos;

    return NGX_ERROR;
}


static void
ngx_mail_proxy_handler(ngx_event_t *ev)
{
    char                   *action, *recv_action, *send_action;
    size_t                  size;
    ssize_t                 n;
    ngx_buf_t              *b;
    ngx_uint_t              do_write;
    ngx_connection_t       *c, *src, *dst;
    ngx_mail_session_t     *s;
    ngx_mail_proxy_conf_t  *pcf;

    c = ev->data;
    s = c->data;

    if (ev->timedout || c->close) {
        c->log->action = "proxying";

        if (c->close) {
            ngx_log_error(NGX_LOG_INFO, c->log, 0, "shutdown timeout");

        } else if (c == s->connection) {
            ngx_log_error(NGX_LOG_INFO, c->log, NGX_ETIMEDOUT,
                          "client timed out");
            c->timedout = 1;

        } else {
            ngx_log_error(NGX_LOG_INFO, c->log, NGX_ETIMEDOUT,
                          "upstream timed out");
        }

        ngx_mail_proxy_close_session(s);
        return;
    }

    if (c == s->connection) {
        if (ev->write) {
            recv_action = "proxying and reading from upstream";
            send_action = "proxying and sending to client";
            src = s->proxy->upstream.connection;
            dst = c;
            b = s->proxy->buffer;

        } else {
            recv_action = "proxying and reading from client";
            send_action = "proxying and sending to upstream";
            src = c;
            dst = s->proxy->upstream.connection;
            b = s->buffer;
        }

    } else {
        if (ev->write) {
            recv_action = "proxying and reading from client";
            send_action = "proxying and sending to upstream";
            src = s->connection;
            dst = c;
            b = s->buffer;

        } else {
            recv_action = "proxying and reading from upstream";
            send_action = "proxying and sending to client";
            src = c;
            dst = s->connection;
            b = s->proxy->buffer;
        }
    }

    do_write = ev->write ? 1 : 0;

    ngx_log_debug3(NGX_LOG_DEBUG_MAIL, ev->log, 0,
                   "mail proxy handler: %ui, #%d > #%d",
                   do_write, src->fd, dst->fd);

    for ( ;; ) {

        if (do_write) {

            size = b->last - b->pos;

            if (size && dst->write->ready) {
                c->log->action = send_action;

                n = dst->send(dst, b->pos, size);

                if (n == NGX_ERROR) {
                    ngx_mail_proxy_close_session(s);
                    return;
                }

                if (n > 0) {
                    b->pos += n;

                    if (b->pos == b->last) {
                        b->pos = b->start;
                        b->last = b->start;
                    }
                }
            }
        }

        size = b->end - b->last;

        if (size && src->read->ready) {
            c->log->action = recv_action;

            n = src->recv(src, b->last, size);

            if (n == NGX_AGAIN || n == 0) {
                break;
            }

            if (n > 0) {
                do_write = 1;
                b->last += n;

                continue;
            }

            if (n == NGX_ERROR) {
                src->read->eof = 1;
            }
        }

        break;
    }

    c->log->action = "proxying";

    if ((s->connection->read->eof && s->buffer->pos == s->buffer->last)
        || (s->proxy->upstream.connection->read->eof
            && s->proxy->buffer->pos == s->proxy->buffer->last)
        || (s->connection->read->eof
            && s->proxy->upstream.connection->read->eof))
    {
        action = c->log->action;
        c->log->action = NULL;
        ngx_log_error(NGX_LOG_INFO, c->log, 0, "proxied session done");
        c->log->action = action;

        ngx_mail_proxy_close_session(s);
        return;
    }

    if (ngx_handle_write_event(dst->write, 0) != NGX_OK) {
        ngx_mail_proxy_close_session(s);
        return;
    }

    if (ngx_handle_read_event(dst->read, 0) != NGX_OK) {
        ngx_mail_proxy_close_session(s);
        return;
    }

    if (ngx_handle_write_event(src->write, 0) != NGX_OK) {
        ngx_mail_proxy_close_session(s);
        return;
    }

    if (ngx_handle_read_event(src->read, 0) != NGX_OK) {
        ngx_mail_proxy_close_session(s);
        return;
    }

    if (c == s->connection) {
        pcf = ngx_mail_get_module_srv_conf(s, ngx_mail_proxy_module);
        ngx_add_timer(c->read, pcf->timeout);
    }
}


static void
ngx_mail_proxy_upstream_error(ngx_mail_session_t *s)
{
    if (s->proxy->upstream.connection) {
        ngx_log_debug1(NGX_LOG_DEBUG_MAIL, s->connection->log, 0,
                       "close mail proxy connection: %d",
                       s->proxy->upstream.connection->fd);

        ngx_close_connection(s->proxy->upstream.connection);
    }

    if (s->out.len == 0) {
        ngx_mail_session_internal_server_error(s);
        return;
    }

    s->quit = 1;
    ngx_mail_send(s->connection->write);
}


static void
ngx_mail_proxy_internal_server_error(ngx_mail_session_t *s)
{
    if (s->proxy->upstream.connection) {
        ngx_log_debug1(NGX_LOG_DEBUG_MAIL, s->connection->log, 0,
                       "close mail proxy connection: %d",
                       s->proxy->upstream.connection->fd);

        ngx_close_connection(s->proxy->upstream.connection);
    }

    ngx_mail_session_internal_server_error(s);
}


static void
ngx_mail_proxy_close_session(ngx_mail_session_t *s)
{
    if (s->proxy->upstream.connection) {
        ngx_log_debug1(NGX_LOG_DEBUG_MAIL, s->connection->log, 0,
                       "close mail proxy connection: %d",
                       s->proxy->upstream.connection->fd);

        ngx_close_connection(s->proxy->upstream.connection);
    }

    ngx_mail_close_connection(s->connection);
}


static void *
ngx_mail_proxy_create_conf(ngx_conf_t *cf)
{
    ngx_mail_proxy_conf_t  *pcf;

    pcf = ngx_pcalloc(cf->pool, sizeof(ngx_mail_proxy_conf_t));
    if (pcf == NULL) {
        return NULL;
    }

    pcf->enable = NGX_CONF_UNSET;
    pcf->pass_error_message = NGX_CONF_UNSET;
    pcf->xclient = NGX_CONF_UNSET;
    pcf->smtp_auth = NGX_CONF_UNSET;
    pcf->proxy_protocol = NGX_CONF_UNSET;
    pcf->buffer_size = NGX_CONF_UNSET_SIZE;
    pcf->timeout = NGX_CONF_UNSET_MSEC;

    return pcf;
}


static char *
ngx_mail_proxy_merge_conf(ngx_conf_t *cf, void *parent, void *child)
{
    ngx_mail_proxy_conf_t *prev = parent;
    ngx_mail_proxy_conf_t *conf = child;

    ngx_conf_merge_value(conf->enable, prev->enable, 0);
    ngx_conf_merge_value(conf->pass_error_message, prev->pass_error_message, 0);
    ngx_conf_merge_value(conf->xclient, prev->xclient, 1);
    ngx_conf_merge_value(conf->smtp_auth, prev->smtp_auth, 0);
    ngx_conf_merge_value(conf->proxy_protocol, prev->proxy_protocol, 0);
    ngx_conf_merge_size_value(conf->buffer_size, prev->buffer_size,
                              (size_t) ngx_pagesize);
    ngx_conf_merge_msec_value(conf->timeout, prev->timeout, 24 * 60 * 60000);

    return NGX_CONF_OK;
}