prefilter: implement basic prefilter priority order

src/detect.c

@@ -3386,21 +3386,37 @@ int SigAddressPrepareStage1(DetectEngineCtx *de_ctx)
 
         if (!(tmp_s->flags & SIG_FLAG_PREFILTER)) {
             int i;
+            int prefilter_list = DETECT_TBLSIZE;
+
+            /* get the keyword supporting prefilter with the lowest type */
             for (i = 0; i < DETECT_SM_LIST_DETECT_MAX; i++) {
                 SigMatch *sm = tmp_s->sm_lists[i];
                 while (sm != NULL) {
                     if (sigmatch_table[sm->type].SupportsPrefilter != NULL) {
                         if (sigmatch_table[sm->type].SupportsPrefilter(tmp_s) == TRUE) {
+                            prefilter_list = MIN(prefilter_list, sm->type);
+                        }
+                    }
+                    sm = sm->next;
+                }
+            }
+
+            /* apply that keyword as prefilter */
+            if (prefilter_list != DETECT_TBLSIZE) {
+                for (i = 0; i < DETECT_SM_LIST_DETECT_MAX; i++) {
+                    SigMatch *sm = tmp_s->sm_lists[i];
+                    while (sm != NULL) {
+                        if (sm->type == prefilter_list) {
                             tmp_s->prefilter_sm = sm;
                             tmp_s->flags |= SIG_FLAG_PREFILTER;
                             SCLogConfig("sid %u: prefilter is on \"%s\"", tmp_s->id, sigmatch_table[sm->type].name);
                             break;
                         }
-                    }
                         sm = sm->next;
                     }
                 }
             }
+        }
 
         de_ctx->sig_cnt++;
     }

src/detect.h

@@ -1111,6 +1111,27 @@ enum {
     DETECT_PRIORITY,
     DETECT_REV,
     DETECT_CLASSTYPE,
+
+    /* sorted by prefilter priority. Higher in this list means it will be
+     * picked over ones lower in the list */
+    DETECT_ACK,
+    DETECT_SEQ,
+    DETECT_WINDOW,
+    DETECT_IPOPTS,
+    DETECT_FLAGS,
+    DETECT_FRAGBITS,
+    DETECT_FRAGOFFSET,
+    DETECT_TTL,
+    DETECT_TOS,
+    DETECT_ITYPE,
+    DETECT_ICODE,
+    DETECT_ICMP_ID,
+    DETECT_ICMP_SEQ,
+    DETECT_DSIZE,
+
+    DETECT_FLOW,
+    /* end prefilter sort */
+
     DETECT_THRESHOLD,
     DETECT_METADATA,
     DETECT_REFERENCE,
@@ -1119,8 +1140,6 @@ enum {
     DETECT_CONTENT,
     DETECT_URICONTENT,
     DETECT_PCRE,
-    DETECT_ACK,
-    DETECT_SEQ,
     DETECT_DEPTH,
     DETECT_DISTANCE,
     DETECT_WITHIN,
@@ -1134,13 +1153,10 @@ enum {
     DETECT_SAMEIP,
     DETECT_GEOIP,
     DETECT_IPPROTO,
-    DETECT_FLOW,
-    DETECT_WINDOW,
     DETECT_FTPBOUNCE,
     DETECT_ISDATAAT,
     DETECT_ID,
     DETECT_RPC,
-    DETECT_DSIZE,
     DETECT_FLOWVAR,
     DETECT_FLOWVAR_POSTMATCH,
     DETECT_FLOWINT,
@@ -1156,19 +1172,9 @@ enum {
     DETECT_ICMPV4_CSUM,
     DETECT_ICMPV6_CSUM,
     DETECT_STREAM_SIZE,
-    DETECT_TTL,
-    DETECT_ITYPE,
-    DETECT_ICODE,
-    DETECT_TOS,
-    DETECT_ICMP_ID,
-    DETECT_ICMP_SEQ,
     DETECT_DETECTION_FILTER,
 
     DETECT_DECODE_EVENT,
-    DETECT_IPOPTS,
-    DETECT_FLAGS,
-    DETECT_FRAGBITS,
-    DETECT_FRAGOFFSET,
     DETECT_GID,
     DETECT_MARK,