well, so that there are no CRs in spooled messages. However, the message
terminating dot is not recognized between two bare CRs.
+Dec 2023: getting a site to send a body including an "LF . LF" sequence
+followed by SMTP commands is a possible "smtp smuggling" attack. If
+the first (header) line for the message has a proper CRLF then enforce
+that for the body: convert bare LF to a space.
+
Arguments:
- fout a FILE to which to write the message; NULL if skipping
+ fout a FILE to which to write the message; NULL if skipping
+ strict_crlf require full CRLF sequence as a line ending
Returns: One of the END_xxx values indicating why it stopped reading
*/
static int
-read_message_data_smtp(FILE *fout)
+read_message_data_smtp(FILE * fout, BOOL strict_crlf)
{
-int ch_state = 0;
-int ch;
-int linelength = 0;
+enum { s_linestart, s_normal, s_had_cr, s_had_nl_dot, s_had_dot_cr } ch_state =
+ s_linestart;
+int linelength = 0, ch;
while ((ch = (receive_getc)(GETC_BUFFER_UNLIMITED)) != EOF)
{
if (ch == 0) body_zerocount++;
switch (ch_state)
{
- case 0: /* After LF or CRLF */
- if (ch == '.')
- {
- ch_state = 3;
- continue; /* Don't ever write . after LF */
- }
- ch_state = 1;
+ case s_linestart: /* After LF or CRLF */
+ if (ch == '.')
+ {
+ ch_state = s_had_nl_dot;
+ continue; /* Don't ever write . after LF */
+ }
+ ch_state = s_normal;
- /* Else fall through to handle as normal uschar. */
+ /* Else fall through to handle as normal uschar. */
- case 1: /* Normal state */
- if (ch == '\n')
- {
- ch_state = 0;
- body_linecount++;
+ case s_normal: /* Normal state */
+ if (ch == '\r')
+ {
+ ch_state = s_had_cr;
+ continue; /* Don't write the CR */
+ }
+ if (ch == '\n') /* Bare LF at end of line */
+ if (strict_crlf)
+ ch = ' '; /* replace LF with space */
+ else
+ { /* treat as line ending */
+ ch_state = s_linestart;
+ body_linecount++;
+ if (linelength > max_received_linelength)
+ max_received_linelength = linelength;
+ linelength = -1;
+ }
+ break;
+
+ case s_had_cr: /* After (unwritten) CR */
+ body_linecount++; /* Any char ends line */
if (linelength > max_received_linelength)
- max_received_linelength = linelength;
+ max_received_linelength = linelength;
linelength = -1;
- }
- else if (ch == '\r')
- {
- ch_state = 2;
- continue;
- }
- break;
+ if (ch == '\n') /* proper CRLF */
+ ch_state = s_linestart;
+ else
+ {
+ message_size++; /* convert the dropped CR to a stored NL */
+ if (fout && fputc('\n', fout) == EOF) return END_WERROR;
+ cutthrough_data_put_nl();
+ if (ch == '\r') /* CR; do not write */
+ continue;
+ ch_state = s_normal; /* not LF or CR; process as standard */
+ }
+ break;
- case 2: /* After (unwritten) CR */
- body_linecount++;
- if (linelength > max_received_linelength)
- max_received_linelength = linelength;
- linelength = -1;
- if (ch == '\n')
- {
- ch_state = 0;
- }
- else
- {
- message_size++;
- if (fout != NULL && fputc('\n', fout) == EOF) return END_WERROR;
- cutthrough_data_put_nl();
- if (ch != '\r') ch_state = 1; else continue;
- }
- break;
+ case s_had_nl_dot: /* After [CR] LF . */
+ if (ch == '\n') /* [CR] LF . LF */
+ if (strict_crlf)
+ ch = ' '; /* replace LF with space */
+ else
+ return END_DOT;
+ else if (ch == '\r') /* [CR] LF . CR */
+ {
+ ch_state = s_had_dot_cr;
+ continue; /* Don't write the CR */
+ }
+ /* The dot was removed on reaching s_had_nl_dot. For a doubled dot, here,
+ reinstate it to cutthrough. The current ch, dot or not, is passed both to
+ cutthrough and to file below. */
+ else if (ch == '.')
+ {
+ uschar c = ch;
+ cutthrough_data_puts(&c, 1);
+ }
+ ch_state = s_normal;
+ break;
- case 3: /* After [CR] LF . */
- if (ch == '\n')
- return END_DOT;
- if (ch == '\r')
- {
- ch_state = 4;
- continue;
- }
- /* The dot was removed at state 3. For a doubled dot, here, reinstate
- it to cutthrough. The current ch, dot or not, is passed both to cutthrough
- and to file below. */
- if (ch == '.')
- {
- uschar c= ch;
- cutthrough_data_puts(&c, 1);
- }
- ch_state = 1;
- break;
+ case s_had_dot_cr: /* After [CR] LF . CR */
+ if (ch == '\n')
+ return END_DOT; /* Preferred termination */
- case 4: /* After [CR] LF . CR */
- if (ch == '\n') return END_DOT;
- message_size++;
- body_linecount++;
- if (fout != NULL && fputc('\n', fout) == EOF) return END_WERROR;
- cutthrough_data_put_nl();
- if (ch == '\r')
- {
- ch_state = 2;
- continue;
- }
- ch_state = 1;
- break;
+ message_size++; /* convert the dropped CR to a stored NL */
+ body_linecount++;
+ if (fout && fputc('\n', fout) == EOF) return END_WERROR;
+ cutthrough_data_put_nl();
+ if (ch == '\r')
+ {
+ ch_state = s_had_cr;
+ continue; /* CR; do not write */
+ }
+ ch_state = s_normal;
+ break;
}
/* Add the character to the spool file, unless skipping; then loop for the
{
if (message_ended >= END_NOTENDED)
message_ended = chunking_state <= CHUNKING_OFFERED
- ? read_message_data_smtp(NULL)
+ ? read_message_data_smtp(NULL, FALSE)
: read_message_bdat_smtp_wire(NULL);
}
if (f.dot_ends && ptr == 0 && ch == '.')
{
+ /* leading dot while in headers-read mode */
ch = (receive_getc)(GETC_BUFFER_UNLIMITED);
if (ch == '\n' && first_line_ended_crlf == TRUE /* and not TRUE_UNSET */ )
/* dot, LF but we are in CRLF mode. Attack? */
/* Open a new spool file for the data portion of the message. We need
-to access it both via a file descriptor and a stream. Try to make the
+to access it both via a file descriptor and a stdio stream. Try to make the
directory if it isn't there. */
spool_name = spool_fname(US"input", message_subdir, message_id, US"-D");
if (smtp_input)
{
message_ended = chunking_state <= CHUNKING_OFFERED
- ? read_message_data_smtp(spool_data_file)
+ ? read_message_data_smtp(spool_data_file, first_line_ended_crlf)
: spool_wireformat
? read_message_bdat_smtp_wire(spool_data_file)
: read_message_bdat_smtp(spool_data_file);
git://git.exim.org / exim.git / blobdiff