On 6 October 2012 09:12, Bradley Kite <[email protected]> wrote:
> Hi,
>
> I am testing/debugging a network application heap corruption bug (the
> application is also an AgentX subagent), and valgrind is reporting this
> error - which I suspect might be the cause of the problem:
>
> ==5608== Thread 9:
> ==5608== Invalid read of size 8
> ==5608== at 0x4CFF13: handle_subagent_response (subagent.c:550)
> ==5608== by 0x4FB8E3: _sess_process_packet (snmp_api.c:5518)
> ==5608== by 0x4FCFC0: _sess_read (snmp_api.c:6043)
> ==5608== by 0x4FDCA8: snmp_sess_read2 (snmp_api.c:6075)
> ==5608== by 0x4FDD42: snmp_read2 (snmp_api.c:5667)
> ==5608== by 0x4C142A: agent_check_and_process (snmp_agent.c:668)
> ==5608== by 0x47AE95: snmp_loop(void*) (authent.cpp:1609)
> ==5608== by 0x3095007D13: start_thread (in /usr/lib64/
> libpthread-2.15.so)
> ==5608== by 0x30948F167C: clone (in /usr/lib64/libc-2.15.so)
> ==5608== Address 0x4e24c00 is 0 bytes inside a block of size 408 free'd
> ==5608== at 0x4A079AE: free (vg_replace_malloc.c:427)
> ==5608== by 0x4F7877: snmp_sess_close (snmp_api.c:2047)
> ==5608== by 0x4F7D62: snmp_sess_select_info2 (snmp_api.c:6207)
> ==5608== by 0x4C13EF: agent_check_and_process (snmp_agent.c:638)
> ==5608== by 0x47AE95: snmp_loop(void*) (authent.cpp:1609)
> ==5608== by 0x3095007D13: start_thread (in /usr/lib64/
> libpthread-2.15.so)
> ==5608== by 0x30948F167C: clone (in /usr/lib64/libc-2.15.so)
>
> I am able to reliably reproduce this by rapidly querying the agent, then
> restarting the snmpd service on the host, which suggests that the problem
> occurs when the subagent looses its connection to the master.
>
> Any help in fixing this would be greatly appreciated.
>
> Regards
> --
> Brad.
>
In trying to narrow this down, it would appear that when the session is
closed (due to the master agent being shutdown), the following read uses
the previous session's struct snmp_internal_session (*isp) data, so the
"magic" (in the isp->callback_data) does not seem right.
When the session is closed (in snmp_sess_close()) should the
snmp_internal_session have its entry removed?
This is my first time working in the internals of net-snmp so any help
would be appreciated.
Thanks in advance.
--
Brad.
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