frames: make sure we use a lowercase buffer name

Ticket: 8526

As some C protocols accepted case-insensitive frame names,
a rule using the same frame twice with different cases,
ended up using 2 different buffers,
which ended up in triggering a buffer overflow

src/detect-frame.c

@@ -132,6 +132,11 @@ static int DetectFrameSetup(DetectEngineCtx *de_ctx, Signature *s, const char *s
         strlcpy(buffer_name, str, sizeof(buffer_name));
         SCLogDebug("long name: %s", buffer_name);
     }
+    // make sure the buffer name is lowercase
+    // even if the protocol accepted case-insensitive frame name
+    for (size_t i = 0; i < sizeof(buffer_name) && buffer_name[i]; i++) {
+        buffer_name[i] = u8_tolower(buffer_name[i]);
+    }
 
     uint8_t frame_type = (uint8_t)raw_frame_type;
     /* TODO we can have TS and TC specific frames */