diff --git a/dp/ctrl.c b/dp/ctrl.c
index faa37b03b..8e8d4441a 100644
--- a/dp/ctrl.c
+++ b/dp/ctrl.c
@@ -116,6 +116,8 @@ int dp_ctrl_send_json(json_t *root)
     }
 
     socklen_t addr_len = sizeof(struct sockaddr_un);
+    //data is nul terminated according to json_dumps
+    //so strlen(data) is safe here
     int sent = sendto(g_ctrl_fd, data, strlen(data), 0,
                       (struct sockaddr *)&g_client_addr, addr_len);
     DEBUG_CTRL("%s\n", data);
@@ -410,6 +412,7 @@ static int dp_ctrl_add_mac(json_t *msg)
     io_mac_t *mac, *ucmac, *bcmac;
     struct ether_addr oldmac;
     const char *mac_str, *ucmac_str, *bcmac_str, *oldmac_str, *pmac_str;
+    size_t ucl, bcl, oml, pml;
     const char *iface;
     int i, count=0;
     json_t *obj, *nw_obj;
@@ -418,9 +421,17 @@ static int dp_ctrl_add_mac(json_t *msg)
     iface = json_string_value(json_object_get(msg, "iface"));
     mac_str = json_string_value(json_object_get(msg, "mac"));
     ucmac_str = json_string_value(json_object_get(msg, "ucmac"));
+    ucl = json_string_length(json_object_get(msg, "ucmac"));
+
     bcmac_str = json_string_value(json_object_get(msg, "bcmac"));
+    bcl = json_string_length(json_object_get(msg, "bcmac"));
+
     oldmac_str = json_string_value(json_object_get(msg, "oldmac"));
+    oml = json_string_length(json_object_get(msg, "oldmac"));
+
     pmac_str = json_string_value(json_object_get(msg, "pmac"));
+    pml = json_string_length(json_object_get(msg, "pmac"));
+
     obj = json_object_get(msg, "pips");
     if (obj) {
         count = json_array_size(obj);
@@ -460,23 +471,23 @@ static int dp_ctrl_add_mac(json_t *msg)
 
     ether_aton_r(mac_str, &mac->mac);
     mac->ep = ep;
-    if (strlen(ucmac_str) > 0) {
+    if (ucl > 0) {
         ether_aton_r(ucmac_str, &ucmac->mac);
         ucmac->unicast = 1;
         ucmac->ep = ep;
     }
-    if (strlen(bcmac_str) > 0) {
+    if (bcl > 0) {
         ether_aton_r(bcmac_str, &bcmac->mac);
         bcmac->broadcast = 1;
         bcmac->ep = ep;
     }
-    if (strlen(oldmac_str) > 0) {
+    if (oml > 0) {
         ether_aton_r(oldmac_str, &oldmac);
     } else {
         oldmac = mac->mac;
     }
     //for proxymesh ep, we need original ep's MAC to get policy handle
-    if (strlen(pmac_str) > 0) {
+    if (pml > 0) {
         ether_aton_r(pmac_str, &ep->pmac);
     }
     //proxymesh ep, we need original ep's IPs to do xff policy match
diff --git a/dp/dpi/dpi_debug.c b/dp/dpi/dpi_debug.c
index fc35a7328..2accc1ae7 100644
--- a/dp/dpi/dpi_debug.c
+++ b/dp/dpi/dpi_debug.c
@@ -37,6 +37,7 @@ void debug_log(bool print_ts, const char *fmt, ...)
     va_end(args);
 }
 
+//debug purpose only not use in production
 void debug_dump_hex(const uint8_t *ptr, int len)
 {
 #define LINE_LEN (6 + 3 + 16 * 3 + 6 + 16)
diff --git a/dp/dpi/dpi_entry.c b/dp/dpi/dpi_entry.c
index 2fae64613..f5e254467 100755
--- a/dp/dpi/dpi_entry.c
+++ b/dp/dpi/dpi_entry.c
@@ -146,7 +146,7 @@ void dpi_ep_set_server_ver(dpi_packet_t *p, char *ver, int len)
     io_app_t *app = ep_app_map_locate(p->ep, s->server.port, s->ip_proto);
     if (unlikely(app == NULL)) return;
 
-    strncpy(app->version, ver, size);
+    strlcpy(app->version, ver, size);
     app->version[size] = '\0';
 
     DEBUG_LOG(DBG_SESSION, p, "port=%u version=%s\n", s->server.port, app->version);
diff --git a/dp/dpi/dpi_log.c b/dp/dpi/dpi_log.c
index b9a3f8a59..1d53203ea 100644
--- a/dp/dpi/dpi_log.c
+++ b/dp/dpi/dpi_log.c
@@ -574,6 +574,7 @@ static void dpi_dlp_trigger_sig_dir(dpi_packet_t *p, dpi_match_t *m, bool flip,
     // Look for cache
     memset(&log, 0, sizeof(log));
     log.ThreatID = htonl(tprop.id);
+    //sig->conf->name is null terminated
     log.DlpNameHash = sdbm_hash((uint8_t *)(sig->conf->name), strlen(sig->conf->name)*sizeof(char));
 
     if (unlikely(p->ep_mac == NULL)) return;
diff --git a/dp/dpi/dpi_policy.c b/dp/dpi/dpi_policy.c
index 8809b33a1..ced84c475 100644
--- a/dp/dpi/dpi_policy.c
+++ b/dp/dpi/dpi_policy.c
@@ -1572,6 +1572,7 @@ static int fqdn_name_match(struct cds_lfht_node *ht_node, const void *key)
 
 static uint32_t fqdn_name_hash(const void *key)
 {
+    //key is null terminated
     const char *k = key;
     return sdbm_hash((uint8_t *)k, strlen(k)*sizeof(char));
 }
@@ -1813,6 +1814,7 @@ static bool match_fqdn_wildcard_name(char *vhost, char *fqdname)
     int i, j;
 
     strlcpy(dname, vhost, MAX_FQDN_LEN);
+    //dname is null terminated
     for (j = strlen(dname)-2; j > 0;  j--) {
         if (dname[j] == '.') {
             break;
@@ -1945,6 +1947,7 @@ int snooped_fqdn_ipv4_mapping(char *name, uint32_t *ip, int cnt)
     fqdn_name_entry_t *name_entry = NULL;
     dpi_fqdn_hdl_t *hdl = g_fqdn_hdl;
 
+    //name is null terminated
     if (strlen(name) > 0) {
         lower_string(name);
     }
@@ -1960,6 +1963,7 @@ int snooped_fqdn_ipv4_mapping(char *name, uint32_t *ip, int cnt)
     int i, j;
 
     strlcpy(dname, name, MAX_FQDN_LEN);
+    //dname is null terminated
     for (j = strlen(dname)-2; j > 0;  j--) {
         if (dname[j] == '.') {
             break;
diff --git a/dp/dpi/parsers/dpi_dns.c b/dp/dpi/parsers/dpi_dns.c
index a29571750..8d6d89cd2 100644
--- a/dp/dpi/parsers/dpi_dns.c
+++ b/dp/dpi/parsers/dpi_dns.c
@@ -277,7 +277,7 @@ static int dns_question(dpi_packet_t *p, uint8_t *ptr, int len, int shift, int c
 
         if (type == DNS_TYPE_A && questions != NULL) {
             if (jump > 1) {
-                strcpy(questions[(*qt_count)++].question, labels);
+                strlcpy(questions[(*qt_count)++].question, labels, MAX_LABEL_LEN);
             }
         }else if (type == DNS_TYPE_AXFR) {
             DEBUG_LOG(DBG_PARSER, p, "DNS Zone Transfer AXFR.\n");
@@ -323,7 +323,7 @@ static int dns_answer(dpi_packet_t *p, uint8_t *ptr, int len, int shift, int cou
         //ipv4 address
         if (type == DNS_TYPE_A && rd_len == 4 && answers != NULL) {
             if (jump > 1) {
-                strcpy(answers[*aw_count].question, labels);
+                strlcpy(answers[*aw_count].question, labels, MAX_LABEL_LEN);
                 uint8_t *addr = ptr + shift;
                 memcpy(&answers[*aw_count].ip4, addr, 4);
                 answers[*aw_count].ip = true;
@@ -334,8 +334,8 @@ static int dns_answer(dpi_packet_t *p, uint8_t *ptr, int len, int shift, int cou
             if (jump > 1) {
                 int ret = get_dns_name(p, ptr, len, shift, cname);
                 if (ret > 1) {
-                    strcpy(answers[*aw_count].question, labels);
-                    strcpy(answers[*aw_count].cname, cname);
+                    strlcpy(answers[*aw_count].question, labels, MAX_LABEL_LEN);
+                    strlcpy(answers[*aw_count].cname, cname, MAX_LABEL_LEN);
                     answers[*aw_count].ip = false;
                     (*aw_count)++;
                 }
diff --git a/dp/dpi/parsers/dpi_http.c b/dp/dpi/parsers/dpi_http.c
index a701d7e25..c568e9df0 100644
--- a/dp/dpi/parsers/dpi_http.c
+++ b/dp/dpi/parsers/dpi_http.c
@@ -600,11 +600,13 @@ static int http_header_xforwarded_for_token(void *param, uint8_t *ptr, int len,
     }
     ip_str_len = l-ptr;
 
+    //preallocated memory
     ip_str = (char *) calloc(ip_str_len + 1, sizeof(char));
     if (ip_str == NULL) {
         return CONSUME_TOKEN_SKIP_LINE;
     }
     strncpy(ip_str, (char *)ptr, ip_str_len);
+    //ip_str is null terminated
     ip_str[ip_str_len] = '\0';
     s->xff_client_ip = inet_addr(ip_str);
     if (s->xff_client_ip == (uint32_t)(-1)) {
@@ -616,6 +618,7 @@ static int http_header_xforwarded_for_token(void *param, uint8_t *ptr, int len,
 
     DEBUG_LOG(DBG_PARSER, p, "X-Forwarded-For: %s, ip=0x%08x, sess flags=0x%04x\n",ip_str, s->xff_client_ip, s->flags);
 
+    //memory freed
     free(ip_str);
     return CONSUME_TOKEN_SKIP_LINE;
 }
@@ -642,11 +645,10 @@ static int http_header_host_token(void *param, uint8_t *ptr, int len, int token_
         l ++;
     }
     host_str_len = l-ptr;
+    int size = min(host_str_len+1, sizeof(s->vhost));
+    strlcpy((char *)s->vhost, (char *)ptr, size);
 
-    strncpy((char *)s->vhost, (char *)ptr, host_str_len);
-    s->vhost[host_str_len] = '\0';
-
-    s->vhlen = host_str_len;
+    s->vhlen = size-1;
     DEBUG_LOG(DBG_PARSER, p, "vhostname(%s) vhlen(%hu)\n", (char *)s->vhost, s->vhlen);
 
     return CONSUME_TOKEN_SKIP_LINE;
diff --git a/dp/dpi/parsers/dpi_ssl.c b/dp/dpi/parsers/dpi_ssl.c
index acf106ab4..ee7f3aa96 100644
--- a/dp/dpi/parsers/dpi_ssl.c
+++ b/dp/dpi/parsers/dpi_ssl.c
@@ -281,9 +281,9 @@ void ssl_get_sni_v3(dpi_packet_t *p, uint8_t *ptr, ssl_record_t *rec)
             uint16_t namelen = GET_BIG_INT16(tptr);
             tptr += 2;
             //DEBUG_LOG(DBG_PARSER, p, "ssl: snilen(%hu), sniname(%s)\n", namelen,(char *)tptr);
-            strncpy((char *)s->vhost, (char *)tptr, namelen);
-            s->vhost[namelen] = '\0';
-            s->vhlen = namelen;
+            int size = min(namelen+1, sizeof(s->vhost));
+            strlcpy((char *)s->vhost, (char *)tptr, size);
+            s->vhlen = size-1;
             tptr += namelen;
             break;
         } else {
diff --git a/dp/dpi/parsers/dpi_tns.c b/dp/dpi/parsers/dpi_tns.c
index 21f1991b5..96e7b17d8 100644
--- a/dp/dpi/parsers/dpi_tns.c
+++ b/dp/dpi/parsers/dpi_tns.c
@@ -101,8 +101,7 @@ static uint16_t tns_connect_addr(dpi_packet_t *p, uint8_t *tnsbodyptr, uint16_t
                     start = pos;
 
                     SKIP_GROUP()
-                    strncpy(prtcl, (char *)(tnsbodyptr + start), pos - start);
-                    prtcl[pos - start] = '\0';
+                    strlcpy(prtcl, (char *)(tnsbodyptr + start), pos - start+1);
 
                     DEBUG_LOG(DBG_PARSER, p, "tns: connect: protocol (%s)\n",prtcl);
 
@@ -125,8 +124,7 @@ static uint16_t tns_connect_addr(dpi_packet_t *p, uint8_t *tnsbodyptr, uint16_t
                     } else {
                         if (pos - start > 0) {
                             char tmport[pos - start + 1];
-                            strncpy(tmport, (char *)(tnsbodyptr + start), pos - start);
-                            tmport[pos - start] = '\0';
+                            strlcpy(tmport, (char *)(tnsbodyptr + start), pos - start + 1);
                             DEBUG_LOG(DBG_PARSER, p, "tns: connect: connect port (%s) abnormal \n", tmport);
                             dpi_fire_parser(p);
                             *rc = TNS_NOTPASS;
@@ -148,8 +146,7 @@ static uint16_t tns_connect_addr(dpi_packet_t *p, uint8_t *tnsbodyptr, uint16_t
 
                     SKIP_GROUP()
 
-                    strncpy(tnshost, (char *)(tnsbodyptr + start), pos - start);
-                    tnshost[pos - start] = '\0';
+                    strlcpy(tnshost, (char *)(tnsbodyptr + start), pos - start + 1);
                     DEBUG_LOG(DBG_PARSER, p, "tns: connect: host (%s) \n", tnshost);
                 } else {
                     SKIP_GROUP()
@@ -306,8 +303,7 @@ static uint16_t tns_redir_connect_addr(dpi_packet_t *p, uint8_t *tnsbodyptr, uin
                     start = pos;
                     SKIP_GROUP()
 
-                    strncpy(redirect_prtl, (char *)(tnsbodyptr + start), pos - start);
-                    redirect_prtl[pos - start] = '\0';
+                    strlcpy(redirect_prtl, (char *)(tnsbodyptr + start), pos - start + 1);
 
                     DEBUG_LOG(DBG_PARSER, p, "tns: redirect: connect protocol (%s)\n",redirect_prtl);
 
@@ -331,8 +327,7 @@ static uint16_t tns_redir_connect_addr(dpi_packet_t *p, uint8_t *tnsbodyptr, uin
                     } else {
                         if (pos - start > 0) {
                             char tmport[pos - start + 1];
-                            strncpy(tmport, (char *)(tnsbodyptr + start), pos - start);
-                            tmport[pos - start] = '\0';
+                            strlcpy(tmport, (char *)(tnsbodyptr + start), pos - start + 1);
                             DEBUG_LOG(DBG_PARSER, p, "tns: redirect: connect port (%s) abnormal \n", tmport);
                         }
                     }
@@ -350,8 +345,7 @@ static uint16_t tns_redir_connect_addr(dpi_packet_t *p, uint8_t *tnsbodyptr, uin
 
                     SKIP_GROUP()
 
-                    strncpy(host, (char *)(tnsbodyptr + start), pos - start);
-                    host[pos - start] = '\0';
+                    strlcpy(host, (char *)(tnsbodyptr + start), pos - start + 1);
 
                     DEBUG_LOG(DBG_PARSER, p, "tns: redirect: host (%s)\n", host);
                     if ( pos - start > 6) {
diff --git a/dp/dpi/sig/dpi_sig.c b/dp/dpi/sig/dpi_sig.c
index c9bcfdc53..db1e0a9fd 100644
--- a/dp/dpi/sig/dpi_sig.c
+++ b/dp/dpi/sig/dpi_sig.c
@@ -5,7 +5,7 @@
 uint32_t DlpRuleCount = 0;
 
 #define MAX_USER_SIG_COUNT (DPI_SIG_MAX_USER_SIG_ID - DPI_SIG_MIN_USER_SIG_ID + 1)
-#define MAX_USER_SIG_LEN 1280//1024+256
+#define MAX_USER_SIG_LEN 2048
 
 static dpi_sigopt_status_t
 dpi_dlp_parse_opts_routine (dpi_dlp_parser_t *parser, char **opts, int count,
@@ -75,6 +75,7 @@ dpi_dlp_parse_opts_routine (dpi_dlp_parser_t *parser, char **opts, int count,
         DEBUG_ERROR(DBG_ERROR, "too many dlp rule (%d) created, max allowed is (%d) ", DlpRuleCount, MAX_USER_SIG_COUNT);
         return DPI_SIGOPT_TOO_MANY_DLP_RULE;
     }
+    //conf->text null terminated
     if (strlen(conf->text) >= MAX_USER_SIG_LEN) {
         DEBUG_ERROR(DBG_ERROR, "dlp rule len(%d) too long, max allowed is (%d) ", strlen(conf->text), MAX_USER_SIG_LEN);
         return DPI_SIGOPT_VALUE_TOO_LONG;
@@ -195,6 +196,7 @@ dpi_dlp_parse_rule (dpi_dlp_parser_t *parser, char **opts, int count,
     dpi_sig_macro_sig_t *macro;
     dpi_sig_t *sig;
     int i;
+    //text is null terminated
     int text_len = strlen(text);
 
     for (i = 0; i < count; i ++) {
diff --git a/dp/utils/helper.c b/dp/utils/helper.c
index a3dab14ca..d3f828939 100755
--- a/dp/utils/helper.c
+++ b/dp/utils/helper.c
@@ -30,7 +30,7 @@ size_t strlcpy (char *dst, const char *src, size_t siz)
     if (n == 0) {
         if (siz != 0)
             *d = '\0';      /* NUL-terminate dst */
-        while (*s++)
+        while (s&&*s++)     /* avoid dereference a NUL pointer, get length of src*/
             ;
     }