src/imap-login/imap-login-client.c

/* Copyright (c) 2002-2018 Dovecot authors, see the included COPYING file */

#include "login-common.h"
#include "buffer.h"
#include "ioloop.h"
#include "istream.h"
#include "ostream.h"
#include "safe-memset.h"
#include "str.h"
#include "imap-parser.h"
#include "imap-id.h"
#include "imap-resp-code.h"
#include "master-service.h"
#include "master-service-ssl-settings.h"
#include "master-auth.h"
#include "imap-login-client.h"
#include "client-authenticate.h"
#include "auth-client.h"
#include "imap-proxy.h"
#include "imap-quote.h"
#include "imap-login-commands.h"
#include "imap-login-settings.h"

#if LOGIN_MAX_INBUF_SIZE < 1024+2
#  error LOGIN_MAX_INBUF_SIZE too short to fit all ID command parameters
#endif

/* Disconnect client when it sends too many bad commands */
#define CLIENT_MAX_BAD_COMMANDS 3

/* Skip incoming data until newline is found,
   returns TRUE if newline was found. */
bool client_skip_line(struct imap_client *client)
{
    const unsigned char *data;
    size_t i, data_size;

    data = i_stream_get_data(client->common.input, &data_size);

    for (i = 0; i < data_size; i++) {
        if (data[i] == '\n') {
            i_stream_skip(client->common.input, i+1);
            return TRUE;
        }
    }

    return FALSE;
}

bool client_handle_parser_error(struct imap_client *client,
                struct imap_parser *parser)
{
    const char *msg;
    enum imap_parser_error parse_error;

    msg = imap_parser_get_error(parser, &parse_error);
    switch (parse_error) {
    case IMAP_PARSE_ERROR_NONE:
        i_unreached();
    case IMAP_PARSE_ERROR_LITERAL_TOO_BIG:
        client_send_reply(&client->common,
                  IMAP_CMD_REPLY_BYE, msg);
        client_destroy(&client->common,
                   t_strconcat("Disconnected: ", msg, NULL));
        return FALSE;
    default:
        break;
    }

    client_send_reply(&client->common, IMAP_CMD_REPLY_BAD, msg);
    client->cmd_finished = TRUE;
    client->skip_line = TRUE;
    return TRUE;
}

static bool is_login_cmd_disabled(struct client *client)
{
    if (client->secured) {
        if (auth_client_find_mech(auth_client, "PLAIN") == NULL) {
            /* no PLAIN authentication, can't use LOGIN command */
            return TRUE;
        }
        return FALSE;
    }
    if (client->set->disable_plaintext_auth)
        return TRUE;
    if (strcmp(client->ssl_set->ssl, "required") == 0)
        return TRUE;
    return FALSE;
}

static const char *get_capability(struct client *client)
{
    struct imap_client *imap_client = (struct imap_client *)client;
    string_t *cap_str = t_str_new(256);
    bool explicit_capability = FALSE;

    if (*imap_client->set->imap_capability == '\0')
        str_append(cap_str, CAPABILITY_BANNER_STRING);
    else if (*imap_client->set->imap_capability != '+') {
        explicit_capability = TRUE;
        str_append(cap_str, imap_client->set->imap_capability);
    } else {
        str_append(cap_str, CAPABILITY_BANNER_STRING);
        str_append_c(cap_str, ' ');
        str_append(cap_str, imap_client->set->imap_capability + 1);
    }

    if (!explicit_capability) {
        if (imap_client->set->imap_literal_minus)
            str_append(cap_str, " LITERAL-");
        else
            str_append(cap_str, " LITERAL+");
    }

    if (client_is_tls_enabled(client) && !client->tls)
        str_append(cap_str, " STARTTLS");
    if (is_login_cmd_disabled(client))
        str_append(cap_str, " LOGINDISABLED");

    client_authenticate_get_capabilities(client, cap_str);
    return str_c(cap_str);
}

static int cmd_capability(struct imap_client *imap_client,
              const struct imap_arg *args ATTR_UNUSED)
{
    struct client *client = &imap_client->common;

    /* Client is required to send CAPABILITY after STARTTLS, so the
       capability resp-code workaround checks only pre-STARTTLS
       CAPABILITY commands. */
    if (!client->starttls)
        imap_client->client_ignores_capability_resp_code = TRUE;
    client_send_raw(client, t_strconcat(
        "* CAPABILITY ", get_capability(client), "\r\n", NULL));
    client_send_reply(client, IMAP_CMD_REPLY_OK,
        "Pre-login capabilities listed, post-login capabilities have more.");
    return 1;
}

static int cmd_starttls(struct imap_client *client,
            const struct imap_arg *args ATTR_UNUSED)
{
    client_cmd_starttls(&client->common);
    return 1;
}

static void
imap_client_notify_starttls(struct client *client,
                bool success, const char *text)
{
    if (success)
        client_send_reply(client, IMAP_CMD_REPLY_OK, text);
    else
        client_send_reply(client, IMAP_CMD_REPLY_BAD, text);
}

static int cmd_noop(struct imap_client *client,
            const struct imap_arg *args ATTR_UNUSED)
{
    client_send_reply(&client->common, IMAP_CMD_REPLY_OK,
              "NOOP completed.");
    return 1;
}

static int cmd_logout(struct imap_client *client,
              const struct imap_arg *args ATTR_UNUSED)
{
    client_send_reply(&client->common, IMAP_CMD_REPLY_BYE, "Logging out");
    client_send_reply(&client->common, IMAP_CMD_REPLY_OK,
              "Logout completed.");
    client_destroy(&client->common, "Aborted login");
    return 1;
}

static int cmd_enable(struct imap_client *client,
              const struct imap_arg *args ATTR_UNUSED)
{
    client_send_raw(&client->common, "* ENABLED\r\n");
    client_send_reply(&client->common, IMAP_CMD_REPLY_OK,
              "ENABLE ignored in non-authenticated state.");
    return 1;
}

static int client_command_execute(struct imap_client *client, const char *cmd,
                  const struct imap_arg *args)
{
    struct imap_login_command *login_cmd;

    login_cmd = imap_login_command_lookup(cmd);
    if (login_cmd == NULL)
        return -2;
    return login_cmd->func(client, args);
}

static bool imap_is_valid_tag(const char *tag)
{
    for (; *tag != '\0'; tag++) {
        switch (*tag) {
        case '+':
        /* atom-specials: */
        case '(':
        case ')':
        case '{':
        case '/':
        case ' ':
        /* list-wildcards: */
        case '%':
        case '*':
        /* quoted-specials: */
        case '"':
        case '\\':
            return FALSE;
        default:
            if (*tag < ' ') /* CTL */
                return FALSE;
            break;
        }
    }
    return TRUE;
}

static int client_parse_command(struct imap_client *client,
                const struct imap_arg **args_r)
{
    switch (imap_parser_read_args(client->parser, 0, 0, args_r)) {
    case -1:
        /* error */
        if (!client_handle_parser_error(client, client->parser)) {
            /* client destroyed */
            return 0;
        }
        return -1;
    case -2:
        /* not enough data */
        return 0;
    default:
        /* we read the entire line - skip over the CRLF */
        if (!client_skip_line(client))
            i_unreached();
        return 1;
    }
}

static bool client_handle_input(struct imap_client *client)
{
    i_assert(!client->common.authenticating);

    if (client->cmd_finished) {
        /* clear the previous command from memory. don't do this
           immediately after handling command since we need the
           cmd_tag to stay some time after authentication commands. */
        client->cmd_tag = NULL;
        client->cmd_name = NULL;
        imap_parser_reset(client->parser);

        /* remove \r\n */
        if (client->skip_line) {
            if (!client_skip_line(client))
                return FALSE;
                        client->skip_line = FALSE;
        }

        client->cmd_finished = FALSE;
    }

    if (client->cmd_tag == NULL) {
                client->cmd_tag = imap_parser_read_word(client->parser);
        if (client->cmd_tag == NULL)
            return FALSE; /* need more data */
        if (!imap_is_valid_tag(client->cmd_tag) ||
            strlen(client->cmd_tag) > IMAP_TAG_MAX_LEN) {
            /* the tag is invalid, don't allow it and don't
               send it back. this attempts to prevent any
               potentially dangerous replies in case someone tries
               to access us using HTTP protocol. */
            client->cmd_tag = "";
        }
    }

    if (client->cmd_name == NULL) {
                client->cmd_name = imap_parser_read_word(client->parser);
        if (client->cmd_name == NULL)
            return FALSE; /* need more data */
    }
    return client->common.v.input_next_cmd(&client->common);
}

static bool imap_client_input_next_cmd(struct client *_client)
{
    struct imap_client *client = (struct imap_client *)_client;
    const struct imap_arg *args;
    bool parsed;
    int ret;

    if (strcasecmp(client->cmd_name, "AUTHENTICATE") == 0) {
        /* SASL-IR may need more space than input buffer's size,
           so we'll handle it as a special case. */
        ret = cmd_authenticate(client, &parsed);
        if (ret == 0 && !parsed)
            return FALSE;
    } else if (strcasecmp(client->cmd_name, "ID") == 0) {
        /* ID extensions allows max. 30 parameters,
           each max. 1024 bytes long. that brings us over the input
           buffer's size, so handle the parameters one at a time */
        ret = cmd_id(client);
        if (ret == 0)
            return FALSE;
        if (ret < 0)
            ret = 1; /* don't send the error reply again */
    } else {
        ret = client_parse_command(client, &args);
        if (ret < 0)
            return TRUE;
        if (ret == 0)
            return FALSE;
        ret = *client->cmd_tag == '\0' ? -1 :
            client_command_execute(client, client->cmd_name, args);
    }

    client->cmd_finished = TRUE;
    if (ret == -2 && strcasecmp(client->cmd_tag, "LOGIN") == 0) {
        client_send_reply(&client->common, IMAP_CMD_REPLY_BAD,
            "First parameter in line is IMAP's command tag, "
            "not the command name. Add that before the command, "
            "like: a login user pass");
    } else if (ret < 0) {
        if (*client->cmd_tag == '\0')
            client->cmd_tag = "*";
        if (++client->common.bad_counter >= CLIENT_MAX_BAD_COMMANDS) {
            client_send_reply(&client->common, IMAP_CMD_REPLY_BYE,
                "Too many invalid IMAP commands.");
            client_destroy(&client->common,
                "Disconnected: Too many invalid commands");
            return FALSE;
        }
        client_send_reply(&client->common, IMAP_CMD_REPLY_BAD,
            "Error in IMAP command received by server.");
    }

    return ret != 0 && !client->common.destroyed;
}

static void imap_client_input(struct client *client)
{
    struct imap_client *imap_client = (struct imap_client *)client;

    if (!client_read(client))
        return;

    client_ref(client);
    o_stream_cork(imap_client->common.output);
    for (;;) {
        if (!auth_client_is_connected(auth_client)) {
            /* we're not currently connected to auth process -
               don't allow any commands */
            client_notify_status(client, FALSE,
                         AUTH_SERVER_WAITING_MSG);
            timeout_remove(&client->to_auth_waiting);

            client->input_blocked = TRUE;
            break;
        } else {
            if (!client_handle_input(imap_client))
                break;
        }
    }
    o_stream_uncork(imap_client->common.output);
    client_unref(&client);
}

static struct client *imap_client_alloc(pool_t pool)
{
    struct imap_client *imap_client;

    imap_client = p_new(pool, struct imap_client, 1);
    return &imap_client->common;
}

static void imap_client_create(struct client *client, void **other_sets)
{
    struct imap_client *imap_client = (struct imap_client *)client;

    imap_client->set = other_sets[0];
    imap_client->parser =
        imap_parser_create(imap_client->common.input,
                   imap_client->common.output,
                   IMAP_LOGIN_MAX_LINE_LENGTH);
    if (imap_client->set->imap_literal_minus)
        imap_parser_enable_literal_minus(imap_client->parser);
    client->io = io_add_istream(client->input, client_input, client);
}

static void imap_client_destroy(struct client *client)
{
    struct imap_client *imap_client = (struct imap_client *)client;

    i_free_and_null(imap_client->proxy_backend_capability);
    imap_parser_unref(&imap_client->parser);
}

static void imap_client_notify_auth_ready(struct client *client)
{
    string_t *greet;

    greet = t_str_new(128);
    str_append(greet, "* OK ");
    str_printfa(greet, "[CAPABILITY %s] ", get_capability(client));
    str_append(greet, client->set->login_greeting);
    str_append(greet, "\r\n");

    client_send_raw(client, str_c(greet));

    client->banner_sent = TRUE;
}

static void imap_client_starttls(struct client *client)
{
    struct imap_client *imap_client = (struct imap_client *)client;

    imap_parser_unref(&imap_client->parser);
    imap_client->parser =
        imap_parser_create(imap_client->common.input,
                   imap_client->common.output,
                   IMAP_LOGIN_MAX_LINE_LENGTH);

    /* CRLF is lost from buffer when streams are reopened. */
    imap_client->skip_line = FALSE;
}

static void ATTR_NULL(3)
client_send_reply_raw(struct client *client,
              const char *prefix, const char *resp_code,
              const char *text, bool tagged)
{
    struct imap_client *imap_client = (struct imap_client *)client;

    T_BEGIN {
        string_t *line = t_str_new(256);

        if (tagged)
            str_append(line, imap_client->cmd_tag);
        else
            str_append_c(line, '*');
        str_append_c(line, ' ');
        str_append(line, prefix);
        str_append_c(line, ' ');
        if (resp_code != NULL)
            str_printfa(line, "[%s] ", resp_code);
        str_append(line, text);
        str_append(line, "\r\n");

        client_send_raw_data(client, str_data(line), str_len(line));
    } T_END;
}

void client_send_reply_code(struct client *client, enum imap_cmd_reply reply,
                const char *resp_code, const char *text)
{
    const char *prefix = "NO";
    bool tagged = TRUE;

    switch (reply) {
    case IMAP_CMD_REPLY_OK:
        prefix = "OK";
        break;
    case IMAP_CMD_REPLY_NO:
        break;
    case IMAP_CMD_REPLY_BAD:
        prefix = "BAD";
        break;
    case IMAP_CMD_REPLY_BYE:
        prefix = "BYE";
        tagged = FALSE;
        break;
    }
    client_send_reply_raw(client, prefix, resp_code, text, tagged);
}

void client_send_reply(struct client *client, enum imap_cmd_reply reply,
               const char *text)
{
    client_send_reply_code(client, reply, NULL, text);
}

static void
imap_client_notify_status(struct client *client, bool bad, const char *text)
{
    if (bad)
        client_send_reply_raw(client, "BAD", "ALERT", text, FALSE);
    else
        client_send_reply_raw(client, "OK", NULL, text, FALSE);
}

static void
imap_client_notify_disconnect(struct client *client,
                  enum client_disconnect_reason reason,
                  const char *text)
{
    if (reason == CLIENT_DISCONNECT_INTERNAL_ERROR) {
        client_send_reply_code(client, IMAP_CMD_REPLY_BYE,
                       IMAP_RESP_CODE_UNAVAILABLE, text);
    } else {
        client_send_reply_code(client, IMAP_CMD_REPLY_BYE, NULL, text);
    }
}

static void imap_login_preinit(void)
{
    login_set_roots = imap_login_setting_roots;
}

static const struct imap_login_command imap_login_commands[] = {
    { "LOGIN", cmd_login },
    { "CAPABILITY", cmd_capability },
    { "STARTTLS", cmd_starttls },
    { "NOOP", cmd_noop },
    { "LOGOUT", cmd_logout },
    { "ENABLE", cmd_enable }
};

static void imap_login_init(void)
{
    imap_login_commands_init();
    imap_login_commands_register(imap_login_commands,
                     N_ELEMENTS(imap_login_commands));
}

static void imap_login_deinit(void)
{
    clients_destroy_all();
    imap_login_commands_deinit();
}

static struct client_vfuncs imap_client_vfuncs = {
    imap_client_alloc,
    imap_client_create,
    imap_client_destroy,
    imap_client_notify_auth_ready,
    imap_client_notify_disconnect,
    imap_client_notify_status,
    imap_client_notify_starttls,
    imap_client_starttls,
    imap_client_input,
    NULL,
    NULL,
    imap_client_auth_result,
    imap_proxy_reset,
    imap_proxy_parse_line,
    imap_proxy_error,
    imap_proxy_get_state,
    client_common_send_raw_data,
    imap_client_input_next_cmd,
    client_common_default_free,
};

static const struct login_binary imap_login_binary = {
    .protocol = "imap",
    .process_name = "imap-login",
    .default_port = 143,
    .default_ssl_port = 993,

    .client_vfuncs = &imap_client_vfuncs,
    .preinit = imap_login_preinit,
    .init = imap_login_init,
    .deinit = imap_login_deinit,

    .sasl_support_final_reply = FALSE
};

int main(int argc, char *argv[])
{
    return login_binary_run(&imap_login_binary, argc, argv);
}