detect/mpm: use fixed constant for stack allocation

instead of smaller run-time value.
Allows easier reading of the code for unbounded stack allocations

Ticket: 8001

src/detect-engine-mpm.c

@@ -216,8 +216,8 @@ static void AppendTransformsToPname(
         /* create comma separated string of the names of the
          * transforms and then shorten it if necessary. Finally
          * use it to construct the 'profile' name for the engine */
-        char xforms[left + 1];
-        memset(xforms, 0, left + 1);
+        char xforms[DETECT_PROFILE_NAME_LEN + 1];
+        memset(xforms, 0, DETECT_PROFILE_NAME_LEN + 1);
         for (int i = 0; i < transforms->cnt; i++) {
             char ttstr[64];
             (void)snprintf(ttstr, sizeof(ttstr), "%s,",
@@ -1524,6 +1524,7 @@ void MpmStoreReportStats(const DetectEngineCtx *de_ctx)
     HashListTableBucket *htb = NULL;
 
     uint32_t stats[MPMB_MAX] = {0};
+    DEBUG_VALIDATE_BUG_ON(de_ctx->buffer_type_id > UINT16_MAX);
     int app_mpms_cnt = de_ctx->buffer_type_id;
     uint32_t appstats[app_mpms_cnt + 1];    // +1 to silence scan-build
     memset(&appstats, 0x00, sizeof(appstats));

src/detect.h

@@ -758,10 +758,11 @@ enum DetectBufferMpmType {
     DETECT_BUFFER_MPM_TYPE_SIZE,
 };
 
+#define DETECT_PROFILE_NAME_LEN 32
 /** \brief one time registration of keywords at start up */
 typedef struct DetectBufferMpmRegistry_ {
     const char *name;
-    char pname[32];             /**< name used in profiling */
+    char pname[DETECT_PROFILE_NAME_LEN]; /**< name used in profiling */
     int direction;              /**< SIG_FLAG_TOSERVER or SIG_FLAG_TOCLIENT */
     int16_t sm_list;
     int16_t sm_list_base;