smtp: handle DATA mode in middle of input parsing

Before:
If the input was such that we'd enter DATA mode in the middle, the
entire data would be passed through SMTPGetLine fn and be processed with
line limits etc in place.

After:
Since we don't want any limits to be enforced on DATA, we pass it to
SMTPPreProcessCommands fn to take care of it differently from the
commands.

Bug 5981

src/app-layer-smtp.c

@@ -1285,6 +1285,15 @@ static int SMTPProcessRequest(SMTPState *state, Flow *f, AppLayerParserState *ps
     }
 }
 
+static inline void ResetLine(SMTPLine *line)
+{
+    if (line != NULL) {
+        line->len = 0;
+        line->delim_len = 0;
+        line->buf = NULL;
+    }
+}
+
 static int SMTPPreProcessCommands(
         SMTPState *state, Flow *f, AppLayerParserState *pstate, SMTPInput *input, SMTPLine *line)
 {
@@ -1299,16 +1308,17 @@ static int SMTPPreProcessCommands(
 
     bool line_complete = false;
     const int32_t input_len = input->len;
+    const int32_t offset = input->consumed;
     for (int32_t i = 0; i < input_len; i++) {
-        if (input->buf[i] == 0x0d) {
-            if (i < input_len - 1 && input->buf[i + 1] == 0x0a) {
+        if (input->buf[offset + i] == 0x0d) {
+            if (i < input_len - 1 && input->buf[offset + i + 1] == 0x0a) {
                 i++;
                 line->delim_len++;
             }
             /* Line is just ending in CR */
             line->delim_len++;
             line_complete = true;
-        } else if (input->buf[i] == 0x0a) {
+        } else if (input->buf[offset + i] == 0x0a) {
             /* Line is just ending in LF */
             line->delim_len++;
             line_complete = true;
@@ -1324,11 +1334,16 @@ static int SMTPPreProcessCommands(
                 SCLogDebug("Possible boundary, yield to GetLine");
                 return 1;
             }
-            int32_t total_consumed = i + 1;
+            /* total_consumed should be input consumed so far + i + 1 */
+            int32_t total_consumed = offset + i + 1;
             int32_t current_line_consumed = total_consumed - input->consumed;
+            DEBUG_VALIDATE_BUG_ON(current_line_consumed < line->delim_len);
             line->buf = input->buf + input->consumed;
             line->len = current_line_consumed - line->delim_len;
             DEBUG_VALIDATE_BUG_ON(line->len < 0);
+            if (line->len < 0) {
+                return -1;
+            }
             input->consumed = total_consumed;
             input->len -= current_line_consumed;
             DEBUG_VALIDATE_BUG_ON(input->consumed + input->len != input->orig_len);
@@ -1374,8 +1389,11 @@ static AppLayerResult SMTPParse(uint8_t direction, Flow *f, SMTPState *state,
                     (state->current_command == SMTP_COMMAND_BDAT)) &&
                 (state->parser_state & SMTP_PARSER_STATE_COMMAND_DATA_MODE)) {
             int ret = SMTPPreProcessCommands(state, f, pstate, &input, &line);
+            DEBUG_VALIDATE_BUG_ON(ret != 0 && ret != -1 && ret != 1);
             if (ret == 0 && input.consumed == input.orig_len) {
                 SCReturnStruct(APP_LAYER_OK);
+            } else if (ret < 0) {
+                SCReturnStruct(APP_LAYER_ERROR);
             }
         }
         AppLayerResult res = SMTPGetLine(state, &input, &line);
@@ -1389,6 +1407,24 @@ static AppLayerResult SMTPParse(uint8_t direction, Flow *f, SMTPState *state,
                 SMTPSetEvent(state, SMTP_DECODER_EVENT_TRUNCATED_LINE);
                 break;
             }
+            /* If request was successfully parsed, reset line as it has already been used
+             * wherever it had to be */
+            ResetLine(&line);
+
+            /* If DATA mode was entered in the middle of input parsing, exempt it from GetLine as we
+             * don't want input limits to be exercised on DATA data. Here, SMTPPreProcessCommands
+             * should either consume all the data or return in case it encounters another boundary.
+             * In case of another boundary, the control should be passed to SMTPGetLine */
+            if ((input.len > 0) && (state->current_command == SMTP_COMMAND_DATA) &&
+                    (state->parser_state & SMTP_PARSER_STATE_COMMAND_DATA_MODE)) {
+                int ret = SMTPPreProcessCommands(state, f, pstate, &input, &line);
+                DEBUG_VALIDATE_BUG_ON(ret != 0 && ret != -1 && ret != 1);
+                if (ret == 0 && input.consumed == input.orig_len) {
+                    SCReturnStruct(APP_LAYER_OK);
+                } else if (ret < 0) {
+                    SCReturnStruct(APP_LAYER_ERROR);
+                }
+            }
             res = SMTPGetLine(state, &input, &line);
         }
         if (res.status == 1)