snmpd crashes when configured as a proxy (with a wrong authentication pass phrase for the agent) and when the manager requests 2 OID

[uaksag]

I have an environment with a manger, a proxy and an agent. The manager requests the proxy (127.0.0.1 below) with a context name (myContext below) corresponding to the agent. The proxy is running snmpd version 5.8.1.pre2 on CentOS 8, compiled and installed from Github. When the proxy received the request, it request the agent (192.168.38.5 below).

Proxy configuration :

rouser myProxyUser
proxy -Cn myContext -r 0 -v 3 -l authNoPriv -u myAgentUser -a SHA -A myAgentAuthPass 192.168.38.5 .1.3

Agent configuration :

rouser myAgentUser

Everything works well. Result on the manger :

snmpget -r 0 -v 3 -l authNoPriv -u myProxyUser -a SHA -A myProxyAuthPass -n myContext 127.0.0.1 SNMPv2-MIB:sysName.0 SNMPv2-MIB:sysDescr.0
SNMPv2-MIB::sysName.0 = STRING: centos-7
SNMPv2-MIB::sysDescr.0 = STRING: Linux centos-7 3.10.0-1062.12.1.el7.x86_64 #1 SMP Tue Feb 4 23:02:59 UTC 2020 x86_64

However, if the authentication pass phrase for the agent on the proxy is wrong, the proxy crashes!

Proxy configuration :

rouser myProxyUser
proxy -Cn myContext -r 0 -v 3 -l authNoPriv -u myAgentUser -a SHA -A myAgentAuthPassWRONG 192.168.38.5 .1.3

Result on the manger :

snmpget -r 0 -v 3 -l authNoPriv -u myProxyUser -a SHA -A myProxyAuthPass -n myContext 127.0.0.1 SNMPv2-MIB:sysName.0 SNMPv2-MIB:sysDescr.0
Timeout: No Response from 127.0.0.1.

And result on the proxy :

/usr/local/sbin/snmpd -Le -f
/var/net-snmp/snmpd.conf: line 47: Warning: Unknown token: ifXTable.
/var/net-snmp/snmpd.conf: line 48: Warning: Unknown token: ifXTable.
NET-SNMP version 5.8.1.pre2
response to proxy request illegal.  We're screwed.
free(): invalid pointer
Aborted (core dumped)

It seems to be caused because the proxy sends a request with 2 OID and receive a response with only 1 OID (1.3.6.1.6.3.15.1.1.5.0, usmStatsWrongDigests). The error message come from agent/mibgroup/ucd-snmp/proxy.c, line 729.

I expect the snmpd to log an error, but not to crashes.

[bvanassche]

A candidate fix has been checked in on the v5.8 and master branches. Please retest.

[uaksag]

The fix works. Thanks!

[bvanassche]

Thanks for the feedback :-)