detect/flowbits: implement prefilter support

Allow for more efficient rules that 'prefilter' on flowbits with 'isset' logic.

This prefilter is enabled by default, which means that if no mpm is present or
no explicit prefilter is used, the flowbits prefilter will be set up for a rule.

flowbits 'isset' prefilter

For rules that have a 'flowbits:isset,<bit>' statement, a "regular" prefilter
facility is created. It means that the rules are removed from the normal
match list(s) and added to a prefilter engine that runs prior to the individual
rule inspection stage.

Implementation: the prefilter is implemented as an RB_TREE of flowbits, with the
rule id's they "enable" stored per tree node. The matching logic is walking the
list of bits set in the flow and looking each of them up in the RB_TREE, adding
the rule ids of each of the matching bits to the list of rule candidates.

The 'isset' prefilter has one important corner case, which is that bits can in
fact be set during the rule evaluation stage. This is different from all other
prefilter engines, that evaluate an immutable state (for the lifetime of the
packets inspection).

flowbits 'set' post-match prefilter

For flowbits 'set' action, special post-match 'prefilter' facilities deal with
this corner case. The high level logic is that these track which 'isset' sigs
depend on them, and add these dependencies to the candidates list when a 'set'
action occurs.

This is implemented in a few steps:

1. flowbits 'set' is flagged
2. when 'set' action occurs the flowbit is added to a "post rule
   match work queue"
3. when the rule evaluation ends, the post-match "prefilter" engine is run
   on each of the flowbits in the "post rule match work queue"
4. these engines ammend the candidates list with the rule id dependencies
   for the flowbit
5. the candidates list is sorted to make sure within the execution for that
   packet the inspection order is maintained

Ticket: #2486.

src/detect-engine-build.c

@@ -668,7 +668,7 @@ static json_t *RulesGroupPrintSghStats(const DetectEngineCtx *de_ctx, const SigG
             any5_cnt++;
         }
 
-        prefilter_cnt += (s->init_data->prefilter_sm != 0);
+        prefilter_cnt += (s->init_data->prefilter_sm != NULL);
         if (s->init_data->mpm_sm == NULL) {
             nonmpm_cnt++;
 

src/detect-engine-prefilter.c

@@ -144,6 +144,35 @@ void DetectRunPrefilterTx(DetectEngineThreadCtx *det_ctx,
     }
 }
 
+/** \brief invoke post-rule match "prefilter" engines
+ *
+ * Invoke prefilter engines that depend on a rule match to run.
+ * e.g. the flowbits:set prefilter that adds sids that depend on
+ * a flowbit "set" to the match array.
+ */
+void PrefilterPostRuleMatch(
+        DetectEngineThreadCtx *det_ctx, const SigGroupHead *sgh, Packet *p, Flow *f)
+{
+    SCLogDebug("post-rule-match engines %p", sgh->post_rule_match_engines);
+    if (sgh->post_rule_match_engines) {
+        PrefilterEngine *engine = sgh->post_rule_match_engines;
+        do {
+            SCLogDebug("running post-rule-match engine");
+            PREFILTER_PROFILING_START(det_ctx);
+            engine->cb.PrefilterPostRule(det_ctx, engine->pectx, p, f);
+            PREFILTER_PROFILING_END(det_ctx, engine->gid);
+
+            if (engine->is_last)
+                break;
+            engine++;
+        } while (1);
+
+        if (det_ctx->pmq.rule_id_array_cnt > 1) {
+            QuickSortSigIntId(det_ctx->pmq.rule_id_array, det_ctx->pmq.rule_id_array_cnt);
+        }
+    }
+}
+
 void Prefilter(DetectEngineThreadCtx *det_ctx, const SigGroupHead *sgh, Packet *p,
         const uint8_t flags, const SignatureMask mask)
 {
@@ -342,6 +371,39 @@ int PrefilterAppendFrameEngine(DetectEngineCtx *de_ctx, SigGroupHead *sgh,
     return 0;
 }
 
+int PrefilterAppendPostRuleEngine(DetectEngineCtx *de_ctx, SigGroupHead *sgh,
+        void (*PrefilterPostRuleFunc)(
+                DetectEngineThreadCtx *det_ctx, const void *pectx, Packet *p, Flow *f),
+        void *pectx, void (*FreeFunc)(void *pectx), const char *name)
+{
+    if (sgh == NULL || PrefilterPostRuleFunc == NULL || pectx == NULL)
+        return -1;
+
+    PrefilterEngineList *e = SCMallocAligned(sizeof(*e), CLS);
+    if (e == NULL)
+        return -1;
+    memset(e, 0x00, sizeof(*e));
+    e->PrefilterPostRule = PrefilterPostRuleFunc;
+    e->pectx = pectx;
+    e->Free = FreeFunc;
+
+    if (sgh->init->post_rule_match_engines == NULL) {
+        sgh->init->post_rule_match_engines = e;
+    } else {
+        PrefilterEngineList *t = sgh->init->post_rule_match_engines;
+        while (t->next != NULL) {
+            t = t->next;
+        }
+
+        t->next = e;
+        e->id = t->id + 1;
+    }
+
+    e->name = name;
+    e->gid = PrefilterStoreGetId(de_ctx, e->name, e->Free);
+    return 0;
+}
+
 static void PrefilterFreeEngineList(PrefilterEngineList *e)
 {
     if (e->Free && e->pectx) {
@@ -396,6 +458,10 @@ void PrefilterCleanupRuleGroup(const DetectEngineCtx *de_ctx, SigGroupHead *sgh)
         PrefilterFreeEngines(de_ctx, sgh->frame_engines);
         sgh->frame_engines = NULL;
     }
+    if (sgh->post_rule_match_engines) {
+        PrefilterFreeEngines(de_ctx, sgh->post_rule_match_engines);
+        sgh->post_rule_match_engines = NULL;
+    }
 }
 
 static int PrefilterSetupRuleGroupSortHelper(const void *a, const void *b)
@@ -589,6 +655,30 @@ void PrefilterSetupRuleGroup(DetectEngineCtx *de_ctx, SigGroupHead *sgh)
             e++;
         }
     }
+    if (sgh->init->post_rule_match_engines != NULL) {
+        uint32_t cnt = 0;
+        for (el = sgh->init->post_rule_match_engines; el != NULL; el = el->next) {
+            cnt++;
+        }
+        sgh->post_rule_match_engines = SCMallocAligned(cnt * sizeof(PrefilterEngine), CLS);
+        if (sgh->post_rule_match_engines == NULL) {
+            return;
+        }
+        memset(sgh->post_rule_match_engines, 0x00, (cnt * sizeof(PrefilterEngine)));
+
+        uint16_t local_id = 0;
+        PrefilterEngine *e = sgh->post_rule_match_engines;
+        for (el = sgh->init->post_rule_match_engines; el != NULL; el = el->next) {
+            e->local_id = local_id++;
+            e->cb.PrefilterPostRule = el->PrefilterPostRule;
+            e->pectx = el->pectx;
+            el->pectx = NULL; // e now owns the ctx
+            e->gid = el->gid;
+            e->is_last = (el->next == NULL);
+            e++;
+        }
+        SCLogDebug("sgh %p max local_id %u", sgh, local_id);
+    }
 }
 
 /* hash table for assigning a unique id to each engine type. */
@@ -889,3 +979,31 @@ int PrefilterGenericMpmPktRegister(DetectEngineCtx *de_ctx, SigGroupHead *sgh, M
     }
     return r;
 }
+
+// TODO move to common file
+#define QUEUE_STEP 16
+
+void PostRuleMatchWorkQueueAppend(
+        DetectEngineThreadCtx *det_ctx, const Signature *s, const int type, const uint32_t value)
+{
+    if (det_ctx->post_rule_work_queue.q == NULL) {
+        det_ctx->post_rule_work_queue.q =
+                SCCalloc(1, sizeof(PostRuleMatchWorkQueueItem) * QUEUE_STEP);
+        BUG_ON(det_ctx->post_rule_work_queue.q == NULL);
+        det_ctx->post_rule_work_queue.size = QUEUE_STEP;
+    } else if (det_ctx->post_rule_work_queue.len == det_ctx->post_rule_work_queue.size) {
+        void *ptr = SCRealloc(
+                det_ctx->post_rule_work_queue.q, (det_ctx->post_rule_work_queue.size + QUEUE_STEP) *
+                                                         sizeof(PostRuleMatchWorkQueueItem));
+        BUG_ON(ptr == NULL);
+        det_ctx->post_rule_work_queue.q = ptr;
+        det_ctx->post_rule_work_queue.size += QUEUE_STEP;
+    }
+    det_ctx->post_rule_work_queue.q[det_ctx->post_rule_work_queue.len].sm_type = type;
+    det_ctx->post_rule_work_queue.q[det_ctx->post_rule_work_queue.len].value = value;
+#ifdef DEBUG
+    det_ctx->post_rule_work_queue.q[det_ctx->post_rule_work_queue.len].id = s->num;
+#endif
+    det_ctx->post_rule_work_queue.len++;
+    SCLogDebug("det_ctx->post_rule_work_queue.len %u", det_ctx->post_rule_work_queue.len);
+}

src/detect-engine-prefilter.h

@@ -1,4 +1,4 @@
-/* Copyright (C) 2016 Open Information Security Foundation
+/* Copyright (C) 2016-2020 Open Information Security Foundation
  *
  * You can copy, redistribute or modify this Program under the terms of
  * the GNU General Public License version 2 as published by the Free
@@ -52,6 +52,10 @@ void Prefilter(DetectEngineThreadCtx *, const SigGroupHead *, Packet *p, const u
 
 int PrefilterAppendEngine(DetectEngineCtx *de_ctx, SigGroupHead *sgh, PrefilterPktFn PrefilterFunc,
         SignatureMask mask, void *pectx, void (*FreeFunc)(void *pectx), const char *name);
+
+void PrefilterPostRuleMatch(
+        DetectEngineThreadCtx *det_ctx, const SigGroupHead *sgh, Packet *p, Flow *f);
+
 int PrefilterAppendPayloadEngine(DetectEngineCtx *de_ctx, SigGroupHead *sgh,
         PrefilterPktFn PrefilterFunc, void *pectx, void (*FreeFunc)(void *pectx), const char *name);
 int PrefilterAppendTxEngine(DetectEngineCtx *de_ctx, SigGroupHead *sgh,
@@ -60,6 +64,10 @@ int PrefilterAppendTxEngine(DetectEngineCtx *de_ctx, SigGroupHead *sgh,
 int PrefilterAppendFrameEngine(DetectEngineCtx *de_ctx, SigGroupHead *sgh,
         PrefilterFrameFn PrefilterFrameFunc, AppProto alproto, uint8_t frame_type, void *pectx,
         void (*FreeFunc)(void *pectx), const char *name);
+int PrefilterAppendPostRuleEngine(DetectEngineCtx *de_ctx, SigGroupHead *sgh,
+        void (*PrefilterPostRuleFunc)(
+                DetectEngineThreadCtx *det_ctx, const void *pectx, Packet *p, Flow *f),
+        void *pectx, void (*FreeFunc)(void *pectx), const char *name);
 
 void DetectRunPrefilterTx(DetectEngineThreadCtx *det_ctx,
         const SigGroupHead *sgh,
@@ -91,4 +99,7 @@ int PrefilterMultiGenericMpmRegister(DetectEngineCtx *de_ctx, SigGroupHead *sgh,
 int PrefilterGenericMpmPktRegister(DetectEngineCtx *de_ctx, SigGroupHead *sgh, MpmCtx *mpm_ctx,
         const DetectBufferMpmRegistry *mpm_reg, int list_id);
 
+void PostRuleMatchWorkQueueAppend(
+        DetectEngineThreadCtx *det_ctx, const Signature *s, const int type, const uint32_t value);
+
 #endif

src/detect-engine-siggroup.c

@@ -81,6 +81,7 @@ void SigGroupHeadInitDataFree(SigGroupHeadInitData *sghid)
     PrefilterFreeEnginesList(sghid->pkt_engines);
     PrefilterFreeEnginesList(sghid->payload_engines);
     PrefilterFreeEnginesList(sghid->frame_engines);
+    PrefilterFreeEnginesList(sghid->post_rule_match_engines);
 
     SCFree(sghid);
 }

src/detect-engine.c

@@ -2535,6 +2535,9 @@ static DetectEngineCtx *DetectEngineCtxInitReal(
         goto error;
     }
 
+    // TODO test enable flowbits prefilter
+    // de_ctx->sm_types_prefilter[DETECT_FLOWBITS] = true;
+
     SigGroupHeadHashInit(de_ctx);
     MpmStoreInit(de_ctx);
     DetectParseDupSigHashInit(de_ctx);
@@ -3539,6 +3542,9 @@ static void DetectEngineThreadCtxFree(DetectEngineThreadCtx *det_ctx)
 
     AlertQueueFree(det_ctx);
 
+    if (det_ctx->post_rule_work_queue.q)
+        SCFree(det_ctx->post_rule_work_queue.q);
+
     if (det_ctx->byte_values != NULL)
         SCFree(det_ctx->byte_values);