Fix community string length copying - correctly handle long strings

src/apps/snmp/snmp_msg.c

@@ -821,8 +821,9 @@ snmp_parse_inbound_frame(struct snmp_request *request)
 
     /* SNMPv3 doesn't use communities */
     /* @todo: Differentiate read/write access */
-    strncpy((char*)request->community, snmp_community, sizeof(request->community));
-    request->community_strlen = (u16_t)strnlen((char*)request->community, sizeof(request->community));
+    strncpy((char*)request->community, snmp_community, SNMP_MAX_COMMUNITY_STR_LEN);
+    request->community[SNMP_MAX_COMMUNITY_STR_LEN] = 0; /* ensure NULL termination (strncpy does NOT guarantee it!) */
+    request->community_strlen = (u16_t)strnlen((char*)request->community, SNMP_MAX_COMMUNITY_STR_LEN);
 
     /* RFC3414 globalData */
     IF_PARSE_EXEC(snmp_asn1_dec_tlv(&pbuf_stream, &tlv));