Strange behavior in SNMP / UDP Code

Paul Whitfield paulw at
Mon Nov 1 07:36:26 UTC 2010

Hi All,

I have seen some strange behaviour with the snmp code and the
network stack and I was wondering if anyone can shed some light on it.

In the SNMP code that is meant to list the current UDP sessions
a sysctl call is made (simplified code) as shown

     int             sname[] =

     if (sysctl(sname, 4, 0, &len, 0, 0) < 0) {

However, the length returned is negative, causing subsequent
code to fail.

Looking at the internals of the network code,
I tracked this back to a negative value in the
the function


It does the following calculation, and the value of udbinfo.ipi_count
is negative.

	n = udbinfo.ipi_count;
	req->oldidx = 2 * (sizeof xig)
		+ (n + n/8) * sizeof(struct xinpcb);

Firstly: I am using an old version of rtems (4.6.6) and so this may
be a problem that has been fixed, however I could not see any
evidence of this in the history of udp_userreq.c



*** YES I know I need to update to a more current version of RTEMS,
it is at the top of my todo list, and has been for a very long time.


Paul Whitfield
Software Engineer

27 Sarich Court, Osborne Park
Perth WA 6017
P:  +61 8 9445 2633
F:  +61 8 9445 1687
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