SIGSEGV received when processing response from SNMP agent using net-snmp library in C

Question

I'm working on a network application using net-snmp to get informations from snmp agents by programming an snmp manager in C. My code should work but everytime I process the variable structure from the net-snmp library I receive a SIGSEGV and I really don't know why. If anyone knows why and/or how to make my code work, please tell me. (I'm developping with CodeBlocks 16.01 IDE, if that helps)

Thank you for your help.

PS : I'm using net-snmp version 5.7.2.1+dfsg-1.

PPS : My computer works with Debian Jessie (8.6.0).

PPPS : It's my first time posting on a forum for help so please be gentle.

source :

/* Include zone, some may not be useful in this application but I used them for testings */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <netinet/in.h>
#include <net-snmp/net-snmp-config.h>
#include <net-snmp/net-snmp-includes.h>
#include <net-snmp/agent/net-snmp-agent-includes.h>
#include <string.h>

/* function prototypes */
int print_result(int status, struct snmp_session *sp, struct snmp_pdu *pdu);

/* Main program */
int main(void)
{

    netsnmp_session session, *ss;
    netsnmp_pdu *pdu;
    netsnmp_pdu *response;
    oid anOID[MAX_OID_LEN];
    size_t anOID_len;
    int status;
    long int *buf[256];

    /* Variables init */
    status = 0;
    response = 0;

    /* SNMP init */
    init_snmp("test");

    /* Session init */
    snmp_sess_init(&session);
    session.peername = "192.168.50.29"; 

    /* SNMP session version */
    session.version = SNMP_VERSION_1;

    /* SNMP session community */
    session.community = "public";
    session.community_len = strlen(session.community);

    /* Session open */
    SOCK_STARTUP;
    ss = snmp_open(&session);
    if (!ss)
    {
       snmp_perror("ack");
       exit(2);
    }

    /* Create PDU */
    pdu = snmp_pdu_create(SNMP_MSG_GET);

    /* Get OID */
    get_node("sysDescr.0", anOID, &anOID_len);
    snmp_add_null_var(pdu, anOID, anOID_len);

    /* Send PDU request and stock response in &response */
    status = snmp_synch_response(ss, pdu, &response);

    /* Response processing */
    print_result(status, ss, response);

    if(response)
    {
        snmp_free_pdu(response);
    }

    /* Closing */
    snmp_close(ss);
    SOCK_CLEANUP;

    return (0);
}

/* Response processing program, where the error I get is */
int print_result(int status, struct snmp_session *sp, struct snmp_pdu *pdu)
{
    char buf[1024];
    struct variable_list *vp;
    int ix;
    struct timeval now;
    struct timezone tz;
    struct tm *tm;

    /* Get the hour */
    gettimeofday(&now, &tz);
    tm = localtime(&now.tv_sec);
    printf("Heure = %.2d:%.2d:%.2d\n", tm->tm_hour, tm->tm_min, tm->tm_sec);

    /* Print SNMP response */
    switch (status)
    {
        /* If no error in snmp_synch_response(); */
        case STAT_SUCCESS :
        {
            vp = pdu->variables;
            /* If no error in response */
            if (pdu->errstat == SNMP_ERR_NOERROR)
            {
                while(vp)   //Possibly error here, but not the point of this question
                {
            /* The error I get is here : everytime I manipulate the vp structure I get the SIGSEGV signal */
                    snprint_variable(buf, sizeof(buf), vp->name, vp->name_length, vp);      

                    printf("%s: %s\n", sp->peername, buf);
                    vp = vp->next_variable;
                }
                return 0;
            }
            /* If error in response */
            else
            {
                for (ix = 1; vp && ix != pdu->errindex; vp = vp->next_variable, ix++)
                {
                    if (vp)
                    {
                        snprint_objid(buf, sizeof(buf), vp->name, vp->name_length);
                    }
                    else
                    {
                        strcpy(buf, "(none)");
                    }
                    printf("%s: %s: %s\n",sp->peername, buf, snmp_errstring(pdu->errstat));
                }
                return -1;
            }
        }break;
        /* If timeout in snmp_synch_response(); */
        case STAT_TIMEOUT :
        {
            fprintf(stdout, "%s: Timeout\n", sp->peername);
            return -1;
        }break;
        /* If error snmp_synch_response(); */
        case STAT_ERROR :
        {
            snmp_perror(sp->peername);
            return -1;
        }break;
        default :
        {
            return -1;
        }
    }
}

Answer 1

I answer to my own question because I found what was wrong with my code.

1. The SNMP version was wrong, the agent I ask uses SNMPv2c not SNMPv1.

2. The OID was wrong (instead of giving its name, giving it's identifier works better) : to know which one to give I used the OiDViEW software to parse the MIB of the agent I use for testing and selected one of them (OIDs).

To make the code work I replaced get_node("sysDescr.0", anOID, &anOID_len); by snmp_parse_oid(".1.3.6.1.2.1.1.5.0", anOID, &anOID_len); and session.version = SNMP_VERSION_1; by session.version = SNMP_VERSION_2c;

After these changes the code works fine.