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/*++
/* NAME
/* smtp_chat 3
/* SUMMARY
/* SMTP client request/response support
/* SYNOPSIS
/* #include "smtp.h"
/*
/* typedef struct {
/* .in +4
/* int code; /* SMTP code, not sanitized */
/* char *dsn; /* enhanced status, sanitized */
/* char *str; /* unmodified SMTP reply */
/* VSTRING *dsn_buf;
/* VSTRING *str_buf;
/* .in -4
/* } SMTP_RESP;
/*
/* void smtp_chat_cmd(session, format, ...)
/* SMTP_SESSION *session;
/* const char *format;
/*
/* DICT *smtp_chat_resp_filter;
/*
/* SMTP_RESP *smtp_chat_resp(session)
/* SMTP_SESSION *session;
/*
/* void smtp_chat_notify(session)
/* SMTP_SESSION *session;
/*
/* void smtp_chat_init(session)
/* SMTP_SESSION *session;
/*
/* void smtp_chat_reset(session)
/* SMTP_SESSION *session;
/* DESCRIPTION
/* This module implements SMTP client support for request/reply
/* conversations, and maintains a limited SMTP transaction log.
/*
/* smtp_chat_cmd() formats a command and sends it to an SMTP server.
/* Optionally, the command is logged.
/*
/* smtp_chat_resp() reads one SMTP server response. It extracts
/* the SMTP reply code and enhanced status code from the text,
/* and concatenates multi-line responses to one string, using
/* a newline as separator. Optionally, the server response
/* is logged.
/* .IP \(bu
/* Postfix never sanitizes the extracted SMTP reply code except
/* to ensure that it is a three-digit code. A malformed reply
/* results in a null extracted SMTP reply code value.
/* .IP \(bu
/* Postfix always sanitizes the extracted enhanced status code.
/* When the server's SMTP status code is 2xx, 4xx or 5xx,
/* Postfix requires that the first digit of the server's
/* enhanced status code matches the first digit of the server's
/* SMTP status code. In case of a mis-match, or when the
/* server specified no status code, the extracted enhanced
/* status code is set to 2.0.0, 4.0.0 or 5.0.0 instead. With
/* SMTP reply codes other than 2xx, 4xx or 5xx, the extracted
/* enhanced status code is set to a default value of 5.5.0
/* (protocol error) for reasons outlined under the next bullet.
/* .IP \(bu
/* Since the SMTP reply code may violate the protocol even
/* when it is correctly formatted, Postfix uses the sanitized
/* extracted enhanced status code to decide whether an error
/* condition is permanent or transient. This means that the
/* caller may have to update the enhanced status code when it
/* discovers that a server reply violates the SMTP protocol,
/* even though it was correctly formatted. This happens when
/* the client and server get out of step due to a broken proxy
/* agent.
/* .PP
/* smtp_chat_resp_filter specifies an optional filter to
/* transform one server reply line before it is parsed. The
/* filter is invoked once for each line of a multi-line reply.
/*
/* smtp_chat_notify() sends a copy of the SMTP transaction log
/* to the postmaster for review. The postmaster notice is sent only
/* when delivery is possible immediately. It is an error to call
/* smtp_chat_notify() when no SMTP transaction log exists.
/*
/* smtp_chat_init() initializes the per-session transaction log.
/* This must be done at the beginning of a new SMTP session.
/*
/* smtp_chat_reset() resets the transaction log. This is
/* typically done at the beginning or end of an SMTP session,
/* or within a session to discard non-error information.
/* DIAGNOSTICS
/* Fatal errors: memory allocation problem, server response exceeds
/* configurable limit.
/* All other exceptions are handled by long jumps (see smtp_stream(3)).
/* SEE ALSO
/* smtp_stream(3) SMTP session I/O support
/* msg(3) generic logging interface
/* 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
/*--*/
/* System library. */
#include <sys_defs.h>
#include <stdlib.h> /* 44BSD stdarg.h uses abort() */
#include <stdarg.h>
#include <ctype.h>
#include <stdlib.h>
#include <setjmp.h>
#include <string.h>
#include <limits.h>
/* Utility library. */
#include <msg.h>
#include <vstring.h>
#include <vstream.h>
#include <argv.h>
#include <stringops.h>
#include <line_wrap.h>
#include <mymalloc.h>
/* Global library. */
#include <recipient_list.h>
#include <deliver_request.h>
#include <smtp_stream.h>
#include <mail_params.h>
#include <mail_addr.h>
#include <post_mail.h>
#include <mail_error.h>
#include <dsn_util.h>
/* Application-specific. */
#include "smtp.h"
/*
* Server reply transformations.
*/
DICT *smtp_chat_resp_filter;
/* smtp_chat_init - initialize SMTP transaction log */
void smtp_chat_init(SMTP_SESSION *session)
{
session->history = 0;
}
/* smtp_chat_reset - reset SMTP transaction log */
void smtp_chat_reset(SMTP_SESSION *session)
{
if (session->history) {
argv_free(session->history);
session->history = 0;
}
}
/* smtp_chat_append - append record to SMTP transaction log */
static void smtp_chat_append(SMTP_SESSION *session, const char *direction,
const char *data)
{
char *line;
if (session->history == 0)
session->history = argv_alloc(10);
line = concatenate(direction, data, (char *) 0);
argv_add(session->history, line, (char *) 0);
myfree(line);
}
/* smtp_chat_cmd - send an SMTP command */
void smtp_chat_cmd(SMTP_SESSION *session, const char *fmt,...)
{
va_list ap;
/*
* Format the command, and update the transaction log.
*/
va_start(ap, fmt);
vstring_vsprintf(session->buffer, fmt, ap);
va_end(ap);
smtp_chat_append(session, "Out: ", STR(session->buffer));
/*
* Optionally log the command first, so we can see in the log what the
* program is trying to do.
*/
if (msg_verbose)
msg_info("> %s: %s", session->namaddrport, STR(session->buffer));
/*
* Send the command to the SMTP server.
*/
smtp_fputs(STR(session->buffer), LEN(session->buffer), session->stream);
/*
* Force flushing of output does not belong here. It is done in the
* smtp_loop() main protocol loop when reading the server response, and
* in smtp_helo() when reading the EHLO response after sending the EHLO
* command.
*
* If we do forced flush here, then we must longjmp() on error, and a
* matching "prepare for disaster" error handler must be set up before
* every smtp_chat_cmd() call.
*/
#if 0
/*
* Flush unsent data to avoid timeouts after slow DNS lookups.
*/
if (time((time_t *) 0) - vstream_ftime(session->stream) > 10)
vstream_fflush(session->stream);
/*
* Abort immediately if the connection is broken.
*/
if (vstream_ftimeout(session->stream))
vstream_longjmp(session->stream, SMTP_ERR_TIME);
if (vstream_ferror(session->stream))
vstream_longjmp(session->stream, SMTP_ERR_EOF);
#endif
}
/* smtp_chat_resp - read and process SMTP server response */
SMTP_RESP *smtp_chat_resp(SMTP_SESSION *session)
{
static SMTP_RESP rdata;
char *cp;
int last_char;
int three_digs = 0;
size_t len;
const char *new_reply;
int chat_append_flag;
int chat_append_skipped = 0;
/*
* Initialize the response data buffer.
*/
if (rdata.str_buf == 0) {
rdata.dsn_buf = vstring_alloc(10);
rdata.str_buf = vstring_alloc(100);
}
/*
* Censor out non-printable characters in server responses. Concatenate
* multi-line server responses. Separate the status code from the text.
* Leave further parsing up to the application.
*
* We can't parse or store input that exceeds var_line_limit, so we just
* skip over it to simplify the remainder of the code below.
*/
VSTRING_RESET(rdata.str_buf);
for (;;) {
last_char = smtp_get(session->buffer, session->stream, var_line_limit,
SMTP_GET_FLAG_SKIP);
/* XXX Update the per-line time limit. */
printable(STR(session->buffer), '?');
if (last_char != '\n')
msg_warn("%s: response longer than %d: %.30s...",
session->namaddrport, var_line_limit, STR(session->buffer));
if (msg_verbose)
msg_info("< %s: %.100s", session->namaddrport, STR(session->buffer));
/*
* Defend against a denial of service attack by limiting the amount
* of multi-line text that we are willing to store.
*/
chat_append_flag = (LEN(rdata.str_buf) < var_line_limit);
if (chat_append_flag)
smtp_chat_append(session, "In: ", STR(session->buffer));
else {
if (chat_append_skipped == 0)
msg_warn("%s: multi-line response longer than %d %.30s...",
session->namaddrport, var_line_limit, STR(rdata.str_buf));
if (chat_append_skipped < INT_MAX)
chat_append_skipped++;
}
/*
* Server reply substitution, for fault-injection testing, or for
* working around broken systems. Use with care.
*/
if (smtp_chat_resp_filter != 0) {
new_reply = dict_get(smtp_chat_resp_filter, STR(session->buffer));
if (new_reply != 0) {
msg_info("%s: replacing server reply \"%s\" with \"%s\"",
session->namaddrport, STR(session->buffer), new_reply);
vstring_strcpy(session->buffer, new_reply);
if (chat_append_flag) {
smtp_chat_append(session, "Replaced-by: ", "");
smtp_chat_append(session, " ", new_reply);
}
} else if (smtp_chat_resp_filter->error != 0) {
msg_warn("%s: table %s:%s lookup error for %s",
session->state->request->queue_id,
smtp_chat_resp_filter->type,
smtp_chat_resp_filter->name,
printable(STR(session->buffer), '?'));
vstream_longjmp(session->stream, SMTP_ERR_DATA);
}
}
if (chat_append_flag) {
if (LEN(rdata.str_buf))
VSTRING_ADDCH(rdata.str_buf, '\n');
vstring_strcat(rdata.str_buf, STR(session->buffer));
}
/*
* Parse into code and text. Do not ignore garbage (see below).
*/
for (cp = STR(session->buffer); *cp && ISDIGIT(*cp); cp++)
/* void */ ;
if ((three_digs = (cp - STR(session->buffer) == 3)) != 0) {
if (*cp == '-')
continue;
if (*cp == ' ' || *cp == 0)
break;
}
/*
* XXX Do not simply ignore garbage in the server reply when ESMTP
* command pipelining is turned on. For example, after sending
* ".<CR><LF>QUIT<CR><LF>" and receiving garbage followed by a
* legitimate 2XX reply, Postfix recognizes the server's QUIT reply
* as the END-OF-DATA reply after garbage, causing mail to be lost.
*
* Without the ability to store per-domain status information in queue
* files, automatic workarounds are problematic:
*
* - Automatically deferring delivery creates a "repeated delivery"
* problem when garbage arrives after the DATA stage. Without the
* workaround, Postfix delivers only once.
*
* - Automatically deferring delivery creates a "no delivery" problem
* when the garbage arrives before the DATA stage. Without the
* workaround, mail might still get through.
*
* - Automatically turning off pipelining for delayed mail affects
* deliveries to correctly implemented servers, and may also affect
* delivery of large mailing lists.
*
* So we leave the decision with the administrator, but we don't force
* them to take action, like we would with automatic deferral. If
* loss of mail is not acceptable then they can turn off pipelining
* for specific sites, or they can turn off pipelining globally when
* they find that there are just too many broken sites.
*/
session->error_mask |= MAIL_ERROR_PROTOCOL;
if (session->features & SMTP_FEATURE_PIPELINING) {
msg_warn("%s: non-%s response from %s: %.100s",
session->state->request->queue_id,
smtp_mode ? "ESMTP" : "LMTP",
session->namaddrport, STR(session->buffer));
if (var_helpful_warnings)
msg_warn("to prevent loss of mail, turn off command pipelining "
"for %s with the %s parameter",
STR(session->iterator->addr),
VAR_LMTP_SMTP(EHLO_DIS_MAPS));
}
}
/*
* Extract RFC 821 reply code and RFC 2034 detail. Use a default detail
* code if none was given.
*
* Ignore out-of-protocol enhanced status codes: codes that accompany 3XX
* replies, or codes whose initial digit is out of sync with the reply
* code.
*
* XXX Potential stability problem. In order to save memory, the queue
* manager stores DSNs in a compact manner:
*
* - empty strings are represented by null pointers,
*
* - the status and reason are required to be non-empty.
*
* Other Postfix daemons inherit this behavior, because they use the same
* DSN support code. This means that everything that receives DSNs must
* cope with null pointers for the optional DSN attributes, and that
* everything that provides DSN information must provide a non-empty
* status and reason, otherwise the DSN support code wil panic().
*
* Thus, when the remote server sends a malformed reply (or 3XX out of
* context) we should not panic() in DSN_COPY() just because we don't
* have a status. Robustness suggests that we supply a status here, and
* that we leave it up to the down-stream code to override the
* server-supplied status in case of an error we can't detect here, such
* as an out-of-order server reply.
*/
VSTRING_TERMINATE(rdata.str_buf);
vstring_strcpy(rdata.dsn_buf, "5.5.0"); /* SAFETY! protocol error */
if (three_digs != 0) {
rdata.code = atoi(STR(session->buffer));
if (strchr("245", STR(session->buffer)[0]) != 0) {
for (cp = STR(session->buffer) + 4; *cp == ' '; cp++)
/* void */ ;
if ((len = dsn_valid(cp)) > 0 && *cp == *STR(session->buffer)) {
vstring_strncpy(rdata.dsn_buf, cp, len);
} else {
vstring_strcpy(rdata.dsn_buf, "0.0.0");
STR(rdata.dsn_buf)[0] = STR(session->buffer)[0];
}
}
} else {
rdata.code = 0;
}
rdata.dsn = STR(rdata.dsn_buf);
rdata.str = STR(rdata.str_buf);
return (&rdata);
}
/* print_line - line_wrap callback */
static void print_line(const char *str, int len, int indent, void *context)
{
VSTREAM *notice = (VSTREAM *) context;
post_mail_fprintf(notice, " %*s%.*s", indent, "", len, str);
}
/* smtp_chat_notify - notify postmaster */
void smtp_chat_notify(SMTP_SESSION *session)
{
const char *myname = "smtp_chat_notify";
VSTREAM *notice;
char **cpp;
/*
* Sanity checks.
*/
if (session->history == 0)
msg_panic("%s: no conversation history", myname);
if (msg_verbose)
msg_info("%s: notify postmaster", myname);
/*
* Construct a message for the postmaster, explaining what this is all
* about. This is junk mail: don't send it when the mail posting service
* is unavailable, and use the double bounce sender address, to prevent
* mail bounce wars. Always prepend one space to message content that we
* generate from untrusted data.
*/
#define NULL_TRACE_FLAGS 0
#define NO_QUEUE_ID ((VSTRING *) 0)
#define LENGTH 78
#define INDENT 4
notice = post_mail_fopen_nowait(mail_addr_double_bounce(),
var_error_rcpt,
MAIL_SRC_MASK_NOTIFY, NULL_TRACE_FLAGS,
SMTPUTF8_FLAG_NONE, NO_QUEUE_ID);
if (notice == 0) {
msg_warn("postmaster notify: %m");
return;
}
post_mail_fprintf(notice, "From: %s (Mail Delivery System)",
mail_addr_mail_daemon());
post_mail_fprintf(notice, "To: %s (Postmaster)", var_error_rcpt);
post_mail_fprintf(notice, "Subject: %s %s client: errors from %s",
var_mail_name, smtp_mode ? "SMTP" : "LMTP",
session->namaddrport);
post_mail_fputs(notice, "");
post_mail_fprintf(notice, "Unexpected response from %s.",
session->namaddrport);
post_mail_fputs(notice, "");
post_mail_fputs(notice, "Transcript of session follows.");
post_mail_fputs(notice, "");
argv_terminate(session->history);
for (cpp = session->history->argv; *cpp; cpp++)
line_wrap(printable(*cpp, '?'), LENGTH, INDENT, print_line,
(void *) notice);
post_mail_fputs(notice, "");
post_mail_fprintf(notice, "For other details, see the local mail logfile");
(void) post_mail_fclose(notice);
}