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view src/mail/ngx_mail_pop3_handler.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 c690a902bfec
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_mail.h>
#include <ngx_mail_pop3_module.h>


static ngx_int_t ngx_mail_pop3_user(ngx_mail_session_t *s, ngx_connection_t *c);
static ngx_int_t ngx_mail_pop3_pass(ngx_mail_session_t *s, ngx_connection_t *c);
static ngx_int_t ngx_mail_pop3_capa(ngx_mail_session_t *s, ngx_connection_t *c,
    ngx_int_t stls);
static ngx_int_t ngx_mail_pop3_stls(ngx_mail_session_t *s, ngx_connection_t *c);
static ngx_int_t ngx_mail_pop3_apop(ngx_mail_session_t *s, ngx_connection_t *c);
static ngx_int_t ngx_mail_pop3_auth(ngx_mail_session_t *s, ngx_connection_t *c);


static u_char  pop3_greeting[] = "+OK POP3 ready" CRLF;
static u_char  pop3_ok[] = "+OK" CRLF;
static u_char  pop3_next[] = "+ " CRLF;
static u_char  pop3_username[] = "+ VXNlcm5hbWU6" CRLF;
static u_char  pop3_password[] = "+ UGFzc3dvcmQ6" CRLF;
static u_char  pop3_invalid_command[] = "-ERR invalid command" CRLF;


void
ngx_mail_pop3_init_session(ngx_mail_session_t *s, ngx_connection_t *c)
{
    u_char                    *p;
    ngx_mail_core_srv_conf_t  *cscf;
    ngx_mail_pop3_srv_conf_t  *pscf;

    pscf = ngx_mail_get_module_srv_conf(s, ngx_mail_pop3_module);
    cscf = ngx_mail_get_module_srv_conf(s, ngx_mail_core_module);

    if (pscf->auth_methods
        & (NGX_MAIL_AUTH_APOP_ENABLED|NGX_MAIL_AUTH_CRAM_MD5_ENABLED))
    {
        if (ngx_mail_salt(s, c, cscf) != NGX_OK) {
            ngx_mail_session_internal_server_error(s);
            return;
        }

        s->out.data = ngx_pnalloc(c->pool, sizeof(pop3_greeting) + s->salt.len);
        if (s->out.data == NULL) {
            ngx_mail_session_internal_server_error(s);
            return;
        }

        p = ngx_cpymem(s->out.data, pop3_greeting, sizeof(pop3_greeting) - 3);
        *p++ = ' ';
        p = ngx_cpymem(p, s->salt.data, s->salt.len);

        s->out.len = p - s->out.data;

    } else {
        ngx_str_set(&s->out, pop3_greeting);
    }

    c->read->handler = ngx_mail_pop3_init_protocol;

    ngx_add_timer(c->read, cscf->timeout);

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

    ngx_mail_send(c->write);
}


void
ngx_mail_pop3_init_protocol(ngx_event_t *rev)
{
    ngx_connection_t    *c;
    ngx_mail_session_t  *s;

    c = rev->data;

    c->log->action = "in auth state";

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

    s = c->data;

    if (s->buffer == NULL) {
        if (ngx_array_init(&s->args, c->pool, 2, sizeof(ngx_str_t))
            == NGX_ERROR)
        {
            ngx_mail_session_internal_server_error(s);
            return;
        }

        s->buffer = ngx_create_temp_buf(c->pool, 128);
        if (s->buffer == NULL) {
            ngx_mail_session_internal_server_error(s);
            return;
        }
    }

    s->mail_state = ngx_pop3_start;
    c->read->handler = ngx_mail_pop3_auth_state;

    ngx_mail_pop3_auth_state(rev);
}


void
ngx_mail_pop3_auth_state(ngx_event_t *rev)
{
    ngx_int_t            rc;
    ngx_connection_t    *c;
    ngx_mail_session_t  *s;

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

    ngx_log_debug0(NGX_LOG_DEBUG_MAIL, c->log, 0, "pop3 auth state");

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

    if (s->out.len) {
        ngx_log_debug0(NGX_LOG_DEBUG_MAIL, c->log, 0, "pop3 send handler busy");
        s->blocked = 1;

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

        return;
    }

    s->blocked = 0;

    rc = ngx_mail_read_command(s, c);

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

        return;
    }

    if (rc == NGX_ERROR) {
        return;
    }

    ngx_str_set(&s->out, pop3_ok);

    if (rc == NGX_OK) {
        switch (s->mail_state) {

        case ngx_pop3_start:

            switch (s->command) {

            case NGX_POP3_USER:
                rc = ngx_mail_pop3_user(s, c);
                break;

            case NGX_POP3_CAPA:
                rc = ngx_mail_pop3_capa(s, c, 1);
                break;

            case NGX_POP3_APOP:
                rc = ngx_mail_pop3_apop(s, c);
                break;

            case NGX_POP3_AUTH:
                rc = ngx_mail_pop3_auth(s, c);
                break;

            case NGX_POP3_QUIT:
                s->quit = 1;
                break;

            case NGX_POP3_NOOP:
                break;

            case NGX_POP3_STLS:
                rc = ngx_mail_pop3_stls(s, c);
                break;

            default:
                rc = NGX_MAIL_PARSE_INVALID_COMMAND;
                break;
            }

            break;

        case ngx_pop3_user:

            switch (s->command) {

            case NGX_POP3_PASS:
                rc = ngx_mail_pop3_pass(s, c);
                break;

            case NGX_POP3_CAPA:
                rc = ngx_mail_pop3_capa(s, c, 0);
                break;

            case NGX_POP3_QUIT:
                s->quit = 1;
                break;

            case NGX_POP3_NOOP:
                break;

            default:
                rc = NGX_MAIL_PARSE_INVALID_COMMAND;
                break;
            }

            break;

        /* suppress warnings */
        case ngx_pop3_passwd:
            break;

        case ngx_pop3_auth_login_username:
            rc = ngx_mail_auth_login_username(s, c, 0);

            ngx_str_set(&s->out, pop3_password);
            s->mail_state = ngx_pop3_auth_login_password;
            break;

        case ngx_pop3_auth_login_password:
            rc = ngx_mail_auth_login_password(s, c);
            break;

        case ngx_pop3_auth_plain:
            rc = ngx_mail_auth_plain(s, c, 0);
            break;

        case ngx_pop3_auth_cram_md5:
            rc = ngx_mail_auth_cram_md5(s, c);
            break;

        case ngx_pop3_auth_external:
            rc = ngx_mail_auth_external(s, c, 0);
            break;
        }
    }

    if (s->buffer->pos < s->buffer->last) {
        s->blocked = 1;
    }

    switch (rc) {

    case NGX_DONE:
        ngx_mail_auth(s, c);
        return;

    case NGX_ERROR:
        ngx_mail_session_internal_server_error(s);
        return;

    case NGX_MAIL_PARSE_INVALID_COMMAND:
        s->mail_state = ngx_pop3_start;
        s->state = 0;

        ngx_str_set(&s->out, pop3_invalid_command);

        /* fall through */

    case NGX_OK:

        s->args.nelts = 0;

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

        if (s->state) {
            s->arg_start = s->buffer->pos;
        }

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

        ngx_mail_send(c->write);
    }
}

static ngx_int_t
ngx_mail_pop3_user(ngx_mail_session_t *s, ngx_connection_t *c)
{
    ngx_str_t  *arg;

#if (NGX_MAIL_SSL)
    if (ngx_mail_starttls_only(s, c)) {
        return NGX_MAIL_PARSE_INVALID_COMMAND;
    }
#endif

    if (s->args.nelts != 1) {
        return NGX_MAIL_PARSE_INVALID_COMMAND;
    }

    arg = s->args.elts;
    s->login.len = arg[0].len;
    s->login.data = ngx_pnalloc(c->pool, s->login.len);
    if (s->login.data == NULL) {
        return NGX_ERROR;
    }

    ngx_memcpy(s->login.data, arg[0].data, s->login.len);

    ngx_log_debug1(NGX_LOG_DEBUG_MAIL, c->log, 0,
                   "pop3 login: \"%V\"", &s->login);

    s->mail_state = ngx_pop3_user;

    return NGX_OK;
}


static ngx_int_t
ngx_mail_pop3_pass(ngx_mail_session_t *s, ngx_connection_t *c)
{
    ngx_str_t  *arg;

    if (s->args.nelts != 1) {
        return NGX_MAIL_PARSE_INVALID_COMMAND;
    }

    arg = s->args.elts;
    s->passwd.len = arg[0].len;
    s->passwd.data = ngx_pnalloc(c->pool, s->passwd.len);
    if (s->passwd.data == NULL) {
        return NGX_ERROR;
    }

    ngx_memcpy(s->passwd.data, arg[0].data, s->passwd.len);

#if (NGX_DEBUG_MAIL_PASSWD)
    ngx_log_debug1(NGX_LOG_DEBUG_MAIL, c->log, 0,
                   "pop3 passwd: \"%V\"", &s->passwd);
#endif

    return NGX_DONE;
}


static ngx_int_t
ngx_mail_pop3_capa(ngx_mail_session_t *s, ngx_connection_t *c, ngx_int_t stls)
{
    ngx_mail_pop3_srv_conf_t  *pscf;

    pscf = ngx_mail_get_module_srv_conf(s, ngx_mail_pop3_module);

#if (NGX_MAIL_SSL)

    if (stls && c->ssl == NULL) {
        ngx_mail_ssl_conf_t  *sslcf;

        sslcf = ngx_mail_get_module_srv_conf(s, ngx_mail_ssl_module);

        if (sslcf->starttls == NGX_MAIL_STARTTLS_ON) {
            s->out = pscf->starttls_capability;
            return NGX_OK;
        }

        if (sslcf->starttls == NGX_MAIL_STARTTLS_ONLY) {
            s->out = pscf->starttls_only_capability;
            return NGX_OK;
        }
    }

#endif

    s->out = pscf->capability;
    return NGX_OK;
}


static ngx_int_t
ngx_mail_pop3_stls(ngx_mail_session_t *s, ngx_connection_t *c)
{
#if (NGX_MAIL_SSL)
    ngx_mail_ssl_conf_t  *sslcf;

    if (c->ssl == NULL) {
        sslcf = ngx_mail_get_module_srv_conf(s, ngx_mail_ssl_module);
        if (sslcf->starttls) {
            s->buffer->pos = s->buffer->start;
            s->buffer->last = s->buffer->start;
            c->read->handler = ngx_mail_starttls_handler;
            return NGX_OK;
        }
    }

#endif

    return NGX_MAIL_PARSE_INVALID_COMMAND;
}


static ngx_int_t
ngx_mail_pop3_apop(ngx_mail_session_t *s, ngx_connection_t *c)
{
    ngx_str_t                 *arg;
    ngx_mail_pop3_srv_conf_t  *pscf;

#if (NGX_MAIL_SSL)
    if (ngx_mail_starttls_only(s, c)) {
        return NGX_MAIL_PARSE_INVALID_COMMAND;
    }
#endif

    if (s->args.nelts != 2) {
        return NGX_MAIL_PARSE_INVALID_COMMAND;
    }

    pscf = ngx_mail_get_module_srv_conf(s, ngx_mail_pop3_module);

    if (!(pscf->auth_methods & NGX_MAIL_AUTH_APOP_ENABLED)) {
        return NGX_MAIL_PARSE_INVALID_COMMAND;
    }

    arg = s->args.elts;

    s->login.len = arg[0].len;
    s->login.data = ngx_pnalloc(c->pool, s->login.len);
    if (s->login.data == NULL) {
        return NGX_ERROR;
    }

    ngx_memcpy(s->login.data, arg[0].data, s->login.len);

    s->passwd.len = arg[1].len;
    s->passwd.data = ngx_pnalloc(c->pool, s->passwd.len);
    if (s->passwd.data == NULL) {
        return NGX_ERROR;
    }

    ngx_memcpy(s->passwd.data, arg[1].data, s->passwd.len);

    ngx_log_debug2(NGX_LOG_DEBUG_MAIL, c->log, 0,
                   "pop3 apop: \"%V\" \"%V\"", &s->login, &s->passwd);

    s->auth_method = NGX_MAIL_AUTH_APOP;

    return NGX_DONE;
}


static ngx_int_t
ngx_mail_pop3_auth(ngx_mail_session_t *s, ngx_connection_t *c)
{
    ngx_int_t                  rc;
    ngx_mail_pop3_srv_conf_t  *pscf;

#if (NGX_MAIL_SSL)
    if (ngx_mail_starttls_only(s, c)) {
        return NGX_MAIL_PARSE_INVALID_COMMAND;
    }
#endif

    pscf = ngx_mail_get_module_srv_conf(s, ngx_mail_pop3_module);

    if (s->args.nelts == 0) {
        s->out = pscf->auth_capability;
        s->state = 0;

        return NGX_OK;
    }

    rc = ngx_mail_auth_parse(s, c);

    switch (rc) {

    case NGX_MAIL_AUTH_LOGIN:

        ngx_str_set(&s->out, pop3_username);
        s->mail_state = ngx_pop3_auth_login_username;

        return NGX_OK;

    case NGX_MAIL_AUTH_LOGIN_USERNAME:

        ngx_str_set(&s->out, pop3_password);
        s->mail_state = ngx_pop3_auth_login_password;

        return ngx_mail_auth_login_username(s, c, 1);

    case NGX_MAIL_AUTH_PLAIN:

        ngx_str_set(&s->out, pop3_next);
        s->mail_state = ngx_pop3_auth_plain;

        return NGX_OK;

    case NGX_MAIL_AUTH_CRAM_MD5:

        if (!(pscf->auth_methods & NGX_MAIL_AUTH_CRAM_MD5_ENABLED)) {
            return NGX_MAIL_PARSE_INVALID_COMMAND;
        }

        if (ngx_mail_auth_cram_md5_salt(s, c, "+ ", 2) == NGX_OK) {
            s->mail_state = ngx_pop3_auth_cram_md5;
            return NGX_OK;
        }

        return NGX_ERROR;

    case NGX_MAIL_AUTH_EXTERNAL:

        if (!(pscf->auth_methods & NGX_MAIL_AUTH_EXTERNAL_ENABLED)) {
            return NGX_MAIL_PARSE_INVALID_COMMAND;
        }

        ngx_str_set(&s->out, pop3_username);
        s->mail_state = ngx_pop3_auth_external;

        return NGX_OK;
    }

    return rc;
}