RE: subagent core dump at startup

So far, I have not been able to reproduce this problem...

Thanks!

Date: Tue, 15 Jun 2010 17:41:27 +0200
Subject: Re: subagent core dump at startup
From: [email protected]
To: [email protected]
CC: [email protected]

On Mon, Jun 14, 2010 at 8:53 PM, W Z <[email protected]> wrote:






We use net-snmp 5.4.2.1.  We had a subagent core dump at system start up.  This happens rarely, i.e., cannot reproduce.

After gdb core file, backtrace shows:
======================================================================

Program terminated with signal 11, Segmentation fault.
[New process 3632]
#0  0xf757b871 in abort () from /lib/libc.so.6

(gdb) bt
#0  0xf757b871 in abort () from /lib/libc.so.6
#1  0xf75b22db in __libc_message () from /lib/libc.so.6

#2  0xf75ba5e5 in _int_free () from /lib/libc.so.6
#3  0xf75baa29 in free () from /lib/libc.so.6
#4  0xf7d58ac7 in snmp_free_pdu (pdu=0x93d3dc8) at snmp_api.c:5088
#5  0xf7d594ba in _sess_process_packet (sessp=0x93600e0, sp=0x93b4d18, isp=0x936a518, transport=0x9372040, opaque=0x93d15b0,

    olength=110, packetptr=0x93f2370 "\001\022", length=72) at snmp_api.c:5354
#6  0xf7d5a7a4 in _sess_read (sessp=0x93600e0, fdset=0xfff1dcec) at snmp_api.c:5707
#7  0xf7d5ac1b in snmp_sess_read (sessp=0x93600e0, fdset=0xfff1dcec) at snmp_api.c:5806

#8  0xf7d596de in snmp_read (fdset=0xfff1dcec) at snmp_api.c:5423
#9  0xf7d2c5aa in snmp_synch_response_cb (ss=0x93b4d18, pdu=0x93d53b8, response=0xfff1de08,
    pcb=0xf7f4fd90 <agentx_check_packet+3>) at snmp_client.c:1016

#10 0xf7f50039 in agentx_synch_input (op=154881304, session=0x93d53b8, reqid=-926200, pdu=0x0, magic=0xf7f23192)
    at mibgroup/agentx/client.c:100
#11 0xf7f506f7 in agentx_register (ss=0x93b4d18, start=0x90ba098, startlen=12, priority=127, range_subid=0, range_ubound=0,

    timeout=-1, flags=0 '\0', contextName=0x90b9ff0 "") at mibgroup/agentx/client.c:213
#12 0xf7f3d99e in agentx_registration_callback (majorID=1, minorID=1, serverarg=0xfff1ded0, clientarg=0x93b4d18)

    at mibgroup/agentx/subagent.c:632
#13 0xf7d7e217 in snmp_call_callbacks (major=1, minor=1, caller_arg=0xfff1ded0) at callback.c:341
#14 0xf7f30de0 in register_mib_reattach_node (s=0x90ba038) at agent_registry.c:768

#15 0xf7f30e2e in register_mib_reattach_node (s=0xfff1df58) at agent_registry.c:772
#16 0xf7f3e752 in agentx_reopen_session (clientreg=0, clientarg=0x0) at mibgroup/agentx/subagent.c:869
#17 0xf7f3b8b7 in subagent_startup (majorID=0, minorID=0, serverarg=0x0, clientarg=0x0) at mibgroup/agentx/subagent.c:99

#18 0xf7d7e217 in snmp_call_callbacks (major=0, minor=0, caller_arg=0x0) at callback.c:341
#19 0xf7d7013d in read_configs () at read_config.c:877
#20 0xf7d4a107 in init_snmp (type=0x824f33c "subsnmpd") at snmp_api.c:811

#21 0x0805005f in main (argc=7, argv=0xfff22194) at main.c:573
======================================================================


I suspect there is a NULL pointer passed to "free()".  However, by looking at function snmp_free_pdu(), it does pointer check before calling "free" function. So, what is the other cause that free() abort?


Also, notice something weird in backtrace #14 and #15, function register_mib_reattach_node() stacked twice?  How could this be?

We only run snmpd and subagent once. There should be no multi-thread issue, I would assume.


What does Valgrind report when you try to reproduce this issue with snmpd running under Valgrind ?

Bart.
 		 	   		  
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