smtp: handle following cmd if LF was found in long line

If a long line had LF post the limit, it should be considered complete
and not wait for the next line to complete it. However, currently, any
following lines were skipped which could sometimes also be important
commands for the entire transaction.

Fix this by setting a flag in case we're truncating a long line but
after having found the LF character.

Bug 5989

src/app-layer-smtp.c

@@ -130,6 +130,7 @@ typedef struct SMTPLine_ {
     /** length of the line in current_line.  Doesn't include the delimiter */
     int32_t len;
     uint8_t delim_len;
+    bool lf_found;
 } SMTPLine;
 
 SCEnumCharMap smtp_decoder_event_table[] = {
@@ -664,6 +665,7 @@ static AppLayerResult SMTPGetLine(SMTPState *state, SMTPInput *input, SMTPLine *
         uint32_t o_consumed = input->consumed;
         input->consumed = lf_idx - input->buf + 1;
         line->len = input->consumed - o_consumed;
+        line->lf_found = true;
         DEBUG_VALIDATE_BUG_ON(line->len < 0);
         if (line->len < 0)
             SCReturnStruct(APP_LAYER_ERROR);
@@ -1418,7 +1420,7 @@ static AppLayerResult SMTPParse(uint8_t direction, Flow *f, SMTPState *state,
     }
 
     SMTPInput input = { .buf = input_buf, .len = input_len, .orig_len = input_len, .consumed = 0 };
-    SMTPLine line = { NULL, 0, 0 };
+    SMTPLine line = { NULL, 0, 0, false };
 
     /* toserver */
     if (direction == 0) {
@@ -1439,7 +1441,9 @@ static AppLayerResult SMTPParse(uint8_t direction, Flow *f, SMTPState *state,
             if (retval != 0)
                 SCReturnStruct(APP_LAYER_ERROR);
             if (line.delim_len == 0 && line.len == SMTP_LINE_BUFFER_LIMIT) {
-                state->discard_till_lf = true;
+                if (!line.lf_found) {
+                    state->discard_till_lf = true;
+                }
                 input.consumed = input.len + 1; // For the newly found LF
                 SMTPSetEvent(state, SMTP_DECODER_EVENT_TRUNCATED_LINE);
                 break;
@@ -1473,7 +1477,9 @@ static AppLayerResult SMTPParse(uint8_t direction, Flow *f, SMTPState *state,
             if (SMTPProcessReply(state, f, pstate, thread_data, &input, &line) != 0)
                 SCReturnStruct(APP_LAYER_ERROR);
             if (line.delim_len == 0 && line.len == SMTP_LINE_BUFFER_LIMIT) {
-                state->discard_till_lf = true;
+                if (!line.lf_found) {
+                    state->discard_till_lf = true;
+                }
                 input.consumed = input.len + 1; // For the newly found LF
                 SMTPSetEvent(state, SMTP_DECODER_EVENT_TRUNCATED_LINE);
                 break;