src/imap-login/imap-proxy.c

	imap-proxy.c revision e95dba8921087afebb8a92c592af3b8ca22ae796
/* Copyright (c) 2004-2009 Dovecot authors, see the included COPYING file */

#include "common.h"
#include "array.h"
#include "ioloop.h"
#include "istream.h"
#include "ostream.h"
#include "base64.h"
#include "str.h"
#include "str-sanitize.h"
#include "safe-memset.h"
#include "client.h"
#include "client-authenticate.h"
#include "imap-resp-code.h"
#include "imap-quote.h"
#include "imap-proxy.h"

#include <stdlib.h>

#define PROXY_FAILURE_MSG \
    "NO ["IMAP_RESP_CODE_UNAVAILABLE"] "AUTH_TEMP_FAILED_MSG

static const char *const *
capabilities_strip_prelogin(const char *const *capabilities)
{
    ARRAY_TYPE(const_string) new_caps_arr;
    const char **new_caps, *str;
    unsigned int count;

    t_array_init(&new_caps_arr, 64);
    for (; *capabilities != NULL; capabilities++) {
        if (strncasecmp(*capabilities, "AUTH=", 5) == 0 ||
            strcasecmp(*capabilities, "STARTTLS") == 0 ||
            strcasecmp(*capabilities, "SASL-IR") == 0 ||
            strcasecmp(*capabilities, "LOGINDISABLED") == 0 ||
            strcasecmp(*capabilities, "LOGIN-REFERRALS") == 0)
            continue;

        str = *capabilities;
        array_append(&new_caps_arr, &str, 1);
    }
    new_caps = array_get_modifiable(&new_caps_arr, &count);
    qsort(new_caps, count, sizeof(*new_caps), i_strcasecmp_p);

    (void)array_append_space(&new_caps_arr);
    return array_idx(&new_caps_arr, 0);
}

static void proxy_write_id(struct imap_client *client, string_t *str)
{
    str_printfa(str, "I ID ("
            "\"x-originating-ip\" \"%s\" "
            "\"x-originating-port\" \"%u\" "
            "\"x-connected-ip\" \"%s\" "
            "\"x-connected-port\" \"%u\")\r\n",
            net_ip2addr(&client->common.ip),
            client->common.remote_port,
            net_ip2addr(&client->common.local_ip),
            client->common.local_port);
}

static void proxy_free_password(struct imap_client *client)
{
    if (client->proxy_password == NULL)
        return;

    safe_memset(client->proxy_password, 0, strlen(client->proxy_password));
    i_free_and_null(client->proxy_password);
}

static void proxy_failed(struct imap_client *client, bool send_tagline)
{
    if (send_tagline)
        client_send_tagline(client, PROXY_FAILURE_MSG);

    login_proxy_free(&client->proxy);
    proxy_free_password(client);
    i_free_and_null(client->proxy_user);
    i_free_and_null(client->proxy_master_user);

    /* call this last - it may destroy the client */
    client_auth_failed(client, TRUE);
}

static void get_plain_auth(struct imap_client *client, string_t *dest)
{
    string_t *str;

    str = t_str_new(128);
    str_append(str, client->proxy_user);
    str_append_c(str, '\0');
    str_append(str, client->proxy_master_user);
    str_append_c(str, '\0');
    str_append(str, client->proxy_password);
    base64_encode(str_data(str), str_len(str), dest);
}

static bool str_array_icmp(const char *const *arr1, const char *const *arr2)
{
    unsigned int i;

    for (i = 0; arr1[i] != NULL; i++) {
        if (arr2[i] == NULL || strcasecmp(arr1[i], arr2[i]) != 0)
            return FALSE;
    }
    return TRUE;
}

static void
client_send_capability_if_needed(struct imap_client *client, string_t *str,
                 const char *capability)
{
    const char *const *backend_capabilities;
    const char *const *proxy_capabilities;

    if (!client->capability_command_used || capability == NULL)
        return;

    /* reset this so that we don't re-send the CAPABILITY in case server
       sends it multiple times */
    client->capability_command_used = FALSE;

    /* client has used CAPABILITY command, so it didn't understand the
       capabilities in the banner. if backend server has different
       capabilities than we advertised already, there's a problem.
       to solve that we'll send the backend's untagged CAPABILITY reply
       and hope that the client understands it */
    backend_capabilities =
        capabilities_strip_prelogin(t_strsplit(capability, " "));
    proxy_capabilities =
        capabilities_strip_prelogin(t_strsplit(login_settings->capability_string, " "));

    if (str_array_icmp(backend_capabilities, proxy_capabilities))
        return;

    str_printfa(str, "* CAPABILITY %s\r\n", capability);
}

static void proxy_write_login(struct imap_client *client, string_t *str)
{
    if (client->capability_command_used)
        str_append(str, "C CAPABILITY\r\n");

    if (client->proxy_master_user == NULL) {
        /* logging in normally - use LOGIN command */
        str_append(str, "L LOGIN ");
        imap_quote_append_string(str, client->proxy_user, FALSE);
        str_append_c(str, ' ');
        imap_quote_append_string(str, client->proxy_password, FALSE);

        proxy_free_password(client);
    } else if (client->proxy_sasl_ir) {
        /* master user login with SASL initial response support */
        str_append(str, "L AUTHENTICATE PLAIN ");
        get_plain_auth(client, str);
        proxy_free_password(client);
    } else {
        /* master user login without SASL initial response */
        str_append(str, "L AUTHENTICATE PLAIN");
    }
    str_append(str, "\r\n");
}

static int proxy_input_banner(struct imap_client *client,
                  struct ostream *output, const char *line)
{
    enum login_proxy_ssl_flags ssl_flags;
    const char *const *capabilities = NULL;
    string_t *str;

    if (strncmp(line, "* OK ", 5) != 0) {
        client_syslog_err(&client->common, t_strdup_printf(
            "proxy: Remote returned invalid banner: %s",
            str_sanitize(line, 160)));
        return -1;
    }

    str = t_str_new(128);
    if (strncmp(line + 5, "[CAPABILITY ", 12) == 0) {
        capabilities = t_strsplit(t_strcut(line + 5 + 12, ']'), " ");
        if (str_array_icase_find(capabilities, "ID"))
            proxy_write_id(client, str);
        if (str_array_icase_find(capabilities, "SASL-IR"))
            client->proxy_sasl_ir = TRUE;
    }

    ssl_flags = login_proxy_get_ssl_flags(client->proxy);
    if ((ssl_flags & PROXY_SSL_FLAG_STARTTLS) != 0) {
        if (capabilities != NULL &&
            !str_array_icase_find(capabilities, "STARTTLS")) {
            client_syslog_err(&client->common,
                "proxy: Remote doesn't support STARTTLS");
            return -1;
        }
        str_append(str, "S STARTTLS\r\n");
    } else {
        proxy_write_login(client, str);
    }

    (void)o_stream_send(output, str_data(str), str_len(str));
    return 0;
}

static int proxy_input_line(struct imap_client *client, const char *line)
{
    struct ostream *output;
    const char *capability;
    string_t *str;

    i_assert(!client->destroyed);

    output = login_proxy_get_ostream(client->proxy);
    if (!client->proxy_seen_banner) {
        /* this is a banner */
        client->proxy_seen_banner = TRUE;
        if (proxy_input_banner(client, output, line) < 0) {
            proxy_failed(client, TRUE);
            return -1;
        }
        return 0;
    } else if (*line == '+') {
        /* AUTHENTICATE started. finish it. */
        str = t_str_new(128);
        get_plain_auth(client, str);
        str_append(str, "\r\n");
        proxy_free_password(client);

        (void)o_stream_send(output, str_data(str), str_len(str));
        return 0;
    } else if (strncmp(line, "S ", 2) == 0) {
        if (strncmp(line, "S OK ", 5) != 0) {
            /* STARTTLS failed */
            client_syslog_err(&client->common, t_strdup_printf(
                "proxy: Remote STARTTLS failed: %s",
                str_sanitize(line + 5, 160)));
            proxy_failed(client, TRUE);
            return -1;
        }
        /* STARTTLS successful, begin TLS negotiation. */
        if (login_proxy_starttls(client->proxy) < 0) {
            proxy_failed(client, TRUE);
            return -1;
        }
        /* i/ostreams changed. */
        output = login_proxy_get_ostream(client->proxy);
        str = t_str_new(128);
        proxy_write_login(client, str);
        (void)o_stream_send(output, str_data(str), str_len(str));
        return 1;
    } else if (strncmp(line, "L OK ", 5) == 0) {
        /* Login successful. Send this line to client. */
        capability = client->proxy_backend_capability;
        if (strncmp(line + 5, "[CAPABILITY ", 12) == 0)
            capability = t_strcut(line + 5 + 12, ']');

        str = t_str_new(128);
        client_send_capability_if_needed(client, str, capability);
        str_append(str, client->cmd_tag);
        str_append(str, line + 1);
        str_append(str, "\r\n");
        (void)o_stream_send(client->output,
                    str_data(str), str_len(str));

        str_truncate(str, 0);
        str_printfa(str, "proxy(%s): started proxying to %s:%u",
                client->common.virtual_user,
                login_proxy_get_host(client->proxy),
                login_proxy_get_port(client->proxy));
        if (strcmp(client->common.virtual_user,
               client->proxy_user) != 0) {
            /* remote username is different, log it */
            str_append_c(str, '/');
            str_append(str, client->proxy_user);
        }
        if (client->proxy_master_user != NULL) {
            str_printfa(str, " (master %s)",
                    client->proxy_master_user);
        }

        (void)client_skip_line(client);
        login_proxy_detach(client->proxy, client->common.input,
                   client->output);

        client->proxy = NULL;
        client->common.input = NULL;
        client->output = NULL;
        client->common.fd = -1;
        client->common.proxying = TRUE;
        client_destroy_success(client, str_c(str));
        return 1;
    } else if (strncmp(line, "L ", 2) == 0) {
        line += 2;
        if (login_settings->verbose_auth) {
            str = t_str_new(128);
            str_printfa(str, "proxy(%s): Login failed to %s:%u",
                    client->common.virtual_user,
                    login_proxy_get_host(client->proxy),
                    login_proxy_get_port(client->proxy));
            if (strcmp(client->common.virtual_user,
                   client->proxy_user) != 0) {
                /* remote username is different, log it */
                str_append_c(str, '/');
                str_append(str, client->proxy_user);
            }
            if (client->proxy_master_user != NULL) {
                str_printfa(str, " (master %s)",
                        client->proxy_master_user);
            }
            str_append(str, ": ");
            if (strncasecmp(line, "NO ", 3) == 0)
                str_append(str, line + 3);
            else
                str_append(str, line);
            i_info("%s", str_c(str));
        }
#define STR_NO_IMAP_RESP_CODE_AUTHFAILED "NO ["IMAP_RESP_CODE_AUTHFAILED"]"
        if (strncmp(line, STR_NO_IMAP_RESP_CODE_AUTHFAILED,
                strlen(STR_NO_IMAP_RESP_CODE_AUTHFAILED)) == 0) {
            /* the remote sent a generic "authentication failed"
               error. replace it with our one, so that in case
               the remote is sending a different error message
               an attacker can't find out what users exist in
               the system. */
            line = "NO "IMAP_AUTH_FAILED_MSG;
        } else if (strncmp(line, "NO [", 4) == 0) {
            /* remote sent some other resp-code. forward it. */
        } else {
            /* there was no [resp-code], so remote isn't Dovecot
               v1.2+. we could either forward the line as-is and
               leak information about what users exist in this
               system, or we could hide other errors than password
               failures. since other errors are pretty rare,
               it's safer to just hide them. they're still
               available in logs though. */
            line = "NO "IMAP_AUTH_FAILED_MSG;
        }
        client_send_tagline(client, line);

        proxy_failed(client, FALSE);
        return -1;
    } else if (strncasecmp(line, "* CAPABILITY ", 13) == 0) {
        i_free(client->proxy_backend_capability);
        client->proxy_backend_capability = i_strdup(line + 13);
        return 0;
    } else {
        /* probably some untagged reply */
        return 0;
    }
}

static void proxy_input(struct imap_client *client)
{
    struct istream *input;
    const char *line;

    if (client->proxy == NULL) {
        /* we're just freeing the proxy */
        return;
    }

    input = login_proxy_get_istream(client->proxy);
    if (input == NULL) {
        if (client->destroyed) {
            /* we came here from client_destroy() */
            return;
        }

        /* failed for some reason, probably server disconnected */
        proxy_failed(client, TRUE);
        return;
    }

    i_assert(!client->destroyed);

    switch (i_stream_read(input)) {
    case -2:
        client_syslog_err(&client->common,
                  "proxy: Remote input buffer full");
        proxy_failed(client, TRUE);
        return;
    case -1:
        client_syslog_err(&client->common,
                  "proxy: Remote disconnected");
        proxy_failed(client, TRUE);
        return;
    }

    while ((line = i_stream_next_line(input)) != NULL) {
        if (proxy_input_line(client, line) != 0)
            break;
    }
}

int imap_proxy_new(struct imap_client *client, const char *host,
           unsigned int port, const char *user, const char *master_user,
           const char *password, enum login_proxy_ssl_flags ssl_flags)
{
    i_assert(user != NULL);
    i_assert(!client->destroyed);

    if (password == NULL) {
        client_syslog_err(&client->common, "proxy: password not given");
        client_send_tagline(client, PROXY_FAILURE_MSG);
        return -1;
    }

    i_assert(client->refcount > 1);

    if (client->destroyed) {
        /* connection_queue_add() decided that we were the oldest
           connection and killed us. */
        return -1;
    }
    if (login_proxy_is_ourself(&client->common, host, port, user)) {
        client_syslog_err(&client->common, "Proxying loops to itself");
        client_send_tagline(client, PROXY_FAILURE_MSG);
        return -1;
    }

    client->proxy = login_proxy_new(&client->common, host, port, ssl_flags,
                    proxy_input, client);
    if (client->proxy == NULL) {
        client_send_tagline(client, PROXY_FAILURE_MSG);
        return -1;
    }

    client->proxy_sasl_ir = FALSE;
    client->proxy_seen_banner = FALSE;
    client->proxy_user = i_strdup(user);
    client->proxy_master_user = i_strdup(master_user);
    client->proxy_password = i_strdup(password);

    /* disable input until authentication is finished */
    if (client->io != NULL)
        io_remove(&client->io);
    return 0;
}