program coredump because "callback_magic" behavior was changed since 5.6.x

Hi All:



1.

My program need to use "callback" function and pass something back.

So, I use "callback_magic" to store an C++ object address.

So, I can get my C++ object and use it my callback function.



My code looks like:

================================

bool CERSnmpSession::open()

{

.....

   m_sessionData.callback = callBack;

   m_sessionData.callback_magic = this;

.....

}



int SNMPSession::callBack(

    int operation,

    struct snmp_session *ses,

    int reqid,

    struct snmp_pdu *pdu,

    void* magic)

{

    SNMPSession* ss = static_cast<SNMPSession*>(magic);

.....

}





2.

The above code works well with net-snmp 5.4.4.

But it coredump with net-snmp 5.7.3 while I set correct username & wrong password to do negative test.



(1).

The reason is that "_sess_process_packet()" (in snmp_api.c in 5.7.3) does:

      if (callback == NULL

                 || callback(NETSNMP_CALLBACK_OP_RECEIVED_MESSAGE, sp,

                                    pdu->reqid, pdu, magic) == 1) {

               if (pdu->command == SNMP_MSG_REPORT) {

                 if (sp->s_snmp_errno == SNMPERR_NOT_IN_TIME_WINDOW ||

                     snmpv3_get_report_type(pdu) ==

                     SNMPERR_NOT_IN_TIME_WINDOW) {

                   /*

                    * trigger immediate retry on recoverable Reports

                    * * (notInTimeWindow), incr_retries == TRUE to prevent

                    * * inifinite resend

                    */

                   if (rp->retries <= sp->retries) {

                     snmp_resend_request(slp, rp, TRUE);

                     break;

                   } else {

                     /* We're done with retries, so no longer waiting for a response */

                     if (magic) {

                              ((struct synch_state*)magic)->waiting = 0;

                     }

                   }

                 } else {

                   if (SNMPV3_IGNORE_UNAUTH_REPORTS) {

                     break;

                   } else { /* Set the state to no longer be waiting, since we're done with retries */

                     if (magic) {

                              ((struct synch_state*)magic)->waiting = 0;  ====> culprit

                     }





(2).

I compared the same code in 5.4.4, it is:

      if (callback == NULL

                 || callback(NETSNMP_CALLBACK_OP_RECEIVED_MESSAGE, sp,

                                    pdu->reqid, pdu, magic) == 1) {

               if (pdu->command == SNMP_MSG_REPORT) {

                 if (sp->s_snmp_errno == SNMPERR_NOT_IN_TIME_WINDOW ||

                     snmpv3_get_report_type(pdu) ==

                     SNMPERR_NOT_IN_TIME_WINDOW) {

                   /*

                    * trigger immediate retry on recoverable Reports

                    * * (notInTimeWindow), incr_retries == TRUE to prevent

                    * * inifinite resend

                    */

                   if (rp->retries <= sp->retries) {

                     snmp_resend_request(slp, rp, TRUE);

                     break;

                   }

                 } else {

                   if (SNMPV3_IGNORE_UNAUTH_REPORTS) {

                     break;

                   }

                 }





(3).

We can see 5.7.3 has extra "((struct synch_state*)magic)->waiting = 0;" than 5.4.4



3.

Can you please help me:

1). If I want to pass private stuff, shall I use "callback_magic" or "myvoid in struct snmp_session" to contain it?

    I tested by using "myvoid" instead of "callback_magic" to contain my private call back data. It works fine.



2). Since "callback_magic" was changed since net-snmp 5.6.x, will net-snmp change "myvoid" in future release?







Thanks and regards

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