smtp: treat a mid-session helo/ehlo like a rset

A HELO or EHLO issued later in the session must clear all buffers and
reset the state exactly as if a RSET had been issued (RFC 5321 4.1.4).
Instead it was ignored, merging the next envelope into the abandoned one
and attributing the delivered message to the abandoned sender.

Handle a HELO/EHLO arriving after an envelope has been started like a
RSET, completing the transaction on the server's 250 reply.

Ticket: OISF#8715

Author: jasonish

src/app-layer-smtp.c

@@ -1414,7 +1414,15 @@ static int SMTPProcessRequest(
             if (r == -1) {
                 SCReturnInt(-1);
             }
-            state->current_command = SMTP_COMMAND_OTHER_CMD;
+            if (state->curr_tx->mail_from != NULL ||
+                    !TAILQ_EMPTY(&state->curr_tx->rcpt_to_list)) {
+                /* Mid-session HELO/EHLO resets the state as if a RSET
+                 * had been issued (RFC 5321 4.1.4). */
+                state->bdat_chunk_idx = 0;
+                state->current_command = SMTP_COMMAND_RSET;
+            } else {
+                state->current_command = SMTP_COMMAND_OTHER_CMD;
+            }
         } else if (line->len >= 9 && SCMemcmpLowercase("mail from", line->buf, 9) == 0) {
             r = SMTPParseCommandMAILFROM(state, line);
             if (r == -1) {