smtp: recover from rejected BDAT commands

A server can reject a BDAT command before the client sends the
advertised chunk. Suricata would keep waiting for those bytes and treat
the rest of the SMTP session as chunk data.

Keeps subsequent SMTP commands and message data in sync with the
server.

Ticket: 8995

src/app-layer-smtp.c

@@ -1086,8 +1086,20 @@ static int SMTPProcessReply(
             SMTPSetEvent(state, SMTP_DECODER_EVENT_DATA_COMMAND_REJECTED);
         }
     } else if (IsReplyToCommand(state, SMTP_COMMAND_BDAT)) {
+        if ((state->parser_state & SMTP_PARSER_STATE_COMMAND_DATA_MODE) &&
+                state->current_command == SMTP_COMMAND_BDAT &&
+                state->cmds_idx + 1 == state->cmds_cnt) {
+            // The server replied before receiving the entire chunk.
+            state->parser_state &= ~SMTP_PARSER_STATE_COMMAND_DATA_MODE;
+        }
         SMTPSetProgressTC(reply_tx, SMTP_RESPONSE_DATA);
     } else if (IsReplyToCommand(state, SMTP_COMMAND_BDAT_LAST)) {
+        if ((state->parser_state & SMTP_PARSER_STATE_COMMAND_DATA_MODE) &&
+                state->current_command == SMTP_COMMAND_BDAT_LAST &&
+                state->cmds_idx + 1 == state->cmds_cnt) {
+            // The server replied before receiving the entire chunk.
+            state->parser_state &= ~SMTP_PARSER_STATE_COMMAND_DATA_MODE;
+        }
         if (reply_tx && !(state->parser_state & SMTP_PARSER_STATE_PARSING_MULTILINE_REPLY)) {
             SMTPTransactionCompleteTC(reply_tx);
         }