SNMP plugin not handling error codes properly

[s-r-engineer]

Relevant telegraf.conf:

[[outputs.file]]
  files = ["stdout"]
[[inputs.snmp]]
  agents = ["udp://127.0.0.1:161"]
  version = 3
  sec_name = "USER"
  auth_protocol = "SHA"
  auth_password = "Some wrong pawwsord"
  sec_level = "authPriv"
  priv_protocol = "AES"
  priv_password = "some wrong password"
  [[inputs.snmp.field]]
    oid = "RFC1213-MIB::sysUpTime.0"
    name = "uptime"

  [[inputs.snmp.field]]
    oid = "RFC1213-MIB::sysName.0"
    name = "source"
    is_tag = true

System info:

Not relevant here

Docker

Steps to reproduce:

1. Start a proper snmpd v3 with authPriv user
2. try to run telegraf
3. profit!!!!1

Expected behavior:

To not to send to output any metrics if there is some problem with authentication or encryption

Actual behavior:

Currently if you are sending an improper SNMPv3 request (like wrong password) you will receive one of special OIDs which is in fact a error message.

Example:

Server config:

snmp user: user
snmp auth protocol: sha
snmp user auth pass: foobaaaaaaar

Telegraf config shown above.
Results here:

telegraf/plugins/inputs/snmp/snmp.go

Line 416 in 5cc4387

if pkt, err := gs.Get([]string{oid}); err != nil {

And OID in ent will be not the same you sent but one of predefined error oids. And telegraf will not threat it like error. It will SEND TO OUTPUT WRONG DATA like it is a proper data

Additional info:

Solution is to check that oid in answer is the requested one

[s-r-engineer]

Totally forgot. Here is the place in code where mentioned that we need to handle that on our own https://github.com/soniah/gosnmp/blob/37eb72902fd19f4c25acdb06f95e07c59b90f363/marshal.go#L279

[Hipska]

Duplicates #7929