[PATCH] RFC1213-MIB::atTable indices are not encoded/resolved correctly

Version: Branch master at commit 0f32c00d89eae2f86b2282ffc50805e059be5492

pysnmp/smi/mibs/RFC1213-MIB.py defines the atNetAddress index of atTable erroneously as IpAddress, while the correct type is NetworkAddress. Since the two types have different OID encoding (NetworkAddress is equivalent to the modern InetAddressType-InetAddress combo and has an extra octet at the beginning which specifies the address type), PySNMP fails to encode or decode atNetAddress index.

To reproduce:

import pysnmp.debug
from pysnmp.smi.builder import MibBuilder
from pysnmp.smi.view import MibViewController
from pysnmp.smi.rfc1902 import ObjectIdentity
from pysnmp.proto.rfc1155 import IpAddress
from pysnmp.proto.rfc1902 import ObjectName
import user

builder = MibBuilder()
builder.loadModules('RFC1213-MIB')
view = MibViewController(builder)

pysnmp.debug.setLogger(pysnmp.debug.Debug('all'))

ident = ObjectIdentity('RFC1213-MIB', 'atIfIndex', 7, IpAddress('143.248.1.177'))
ident.resolveWithMib(view)
print(ident.getOid())

ident2 = ObjectIdentity(ObjectName('1.3.6.1.2.1.3.1.1.1.7.1.143.248.1.177'))
ident2.resolveWithMib(view)
print(ident2.getMibSymbol())

Results in:

2017-10-06 10:37:45,703 pysnmp: running pysnmp version 4.4.1
2017-10-06 10:37:45,703 pysnmp: debug category 'all' enabled
2017-10-06 10:37:45,792 pysnmp: trying DirMibSource('/Users/eugene.kim/.pysnmp/mibs')
2017-10-06 10:37:45,792 pysnmp: addMibSources: new MIB sources [ZipMibSource('pysnmp/smi/mibs'), ZipMibSource('pysnmp/smi/mibs/instances'), DirMibSource('pysnmp_mibs'), DirMibSource('/Users/eugene.kim/.pysnmp/mibs')]
2017-10-06 10:37:45,792 pysnmp: indexMib: re-indexing MIB view
2017-10-06 10:37:45,795 pysnmp: getNodeNameByOid: resolved :1.3.6.1.2.1.3.1.1.1 -> ('iso', 'org', 'dod', 'internet', 'mgmt', 'mib-2', 'at', 'atTable', 'atEntry', 'atIfIndex').()
2017-10-06 10:37:45,795 pysnmp: resolved ('RFC1213-MIB', 'atIfIndex', 7, IpAddress(hexValue='8ff801b1')) into prefix ObjectName('1.3.6.1.2.1.3.1.1.1') and suffix ()
2017-10-06 10:37:45,795 pysnmp: getNodeNameByOid: resolved :(1, 3, 6, 1, 2, 1, 3, 1, 1) -> ('iso', 'org', 'dod', 'internet', 'mgmt', 'mib-2', 'at', 'atTable', 'atEntry').()
2017-10-06 10:37:45,795 pysnmp: resolved indices are (Integer32(7), IpAddress(hexValue='8ff801b1'))
1.3.6.1.2.1.3.1.1.1.7.143.248.1.177
2017-10-06 10:37:45,795 pysnmp: resolving 1.3.6.1.2.1.3.1.1.1.7.1.143.248.1.177 as OID or label
2017-10-06 10:37:45,796 pysnmp: getNodeNameByOid: resolved :1.3.6.1.2.1.3.1.1.1.7.1.143.248.1.177 -> ('iso', 'org', 'dod', 'internet', 'mgmt', 'mib-2', 'at', 'atTable', 'atEntry', 'atIfIndex').7.1.143.248.1.177
2017-10-06 10:37:45,796 pysnmp: resolved (ObjectName('1.3.6.1.2.1.3.1.1.1.7.1.143.248.1.177'),) into prefix ObjectName('1.3.6.1.2.1.3.1.1.1') and suffix ObjectName('7.1.143.248.1.177')
2017-10-06 10:37:45,796 pysnmp: getNodeNameByOid: resolved :1.3.6.1.2.1.3.1.1.1 -> ('iso', 'org', 'dod', 'internet', 'mgmt', 'mib-2', 'at', 'atTable', 'atEntry', 'atIfIndex').()
2017-10-06 10:37:45,796 pysnmp: resolved prefix ObjectName('1.3.6.1.2.1.3.1.1.1') into MIB node MibTableColumn((1, 3, 6, 1, 2, 1, 3, 1, 1, 1), Integer32())
2017-10-06 10:37:45,796 pysnmp: getNodeNameByOid: resolved :(1, 3, 6, 1, 2, 1, 3, 1, 1) -> ('iso', 'org', 'dod', 'internet', 'mgmt', 'mib-2', 'at', 'atTable', 'atEntry').()
Traceback (most recent call last):
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/runpy.py", line 193, in _run_module_as_main
    "__main__", mod_spec)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/Users/eugene.kim/Work/ESI/snmp2es/z.py", line 20, in <module>
    ident2.resolveWithMib(view)
  File "/Users/eugene.kim/venvs/playground36/lib/python3.6/site-packages/pysnmp-4.4.1-py3.6.egg/pysnmp/smi/rfc1902.py", line 450, in resolveWithMib
  File "<string>", line 1223, in getIndicesFromInstId
pysnmp.smi.error.SmiError: Excessive instance identifier sub-OIDs left at MibTableRow((1, 3, 6, 1, 2, 1, 3, 1, 1), None): 177

Note:

• The OID-encoded atNetAddress 143.248.1.177 lacks the NetworkAddress type selector value 1 at the beginning;
• The buggy code could not resolve a correctly encoded index (ident2) because it did not expect the NetworkAddress type selector value before the IP address literal. What happened instead is: 1) the buggy code erroneously decoded the address as 1.143.248.1 (the type selector value plus the first 3 sub-identifiers of the IP address), then 2) raised an exception upon seeing 177, which the last octet of the IP address.

#87 fixes this issue (note: #87 requires etingof/pyasn1#85), to yield correct result:

2017-10-06 10:49:52,165 pysnmp: running pysnmp version 4.4.1
2017-10-06 10:49:52,166 pysnmp: debug category 'all' enabled
2017-10-06 10:49:52,254 pysnmp: trying DirMibSource('/Users/eugene.kim/.pysnmp/mibs')
2017-10-06 10:49:52,254 pysnmp: addMibSources: new MIB sources [ZipMibSource('pysnmp/smi/mibs'), ZipMibSource('pysnmp/smi/mibs/instances'), DirMibSource('pysnmp_mibs'), DirMibSource('/Users/eugene.kim/.pysnmp/mibs')]
2017-10-06 10:49:52,254 pysnmp: indexMib: re-indexing MIB view
2017-10-06 10:49:52,256 pysnmp: getNodeNameByOid: resolved :1.3.6.1.2.1.3.1.1.1 -> ('iso', 'org', 'dod', 'internet', 'mgmt', 'mib-2', 'at', 'atTable', 'atEntry', 'atIfIndex').()
2017-10-06 10:49:52,256 pysnmp: resolved ('RFC1213-MIB', 'atIfIndex', 7, IpAddress(hexValue='8ff801b1')) into prefix ObjectName('1.3.6.1.2.1.3.1.1.1') and suffix ()
2017-10-06 10:49:52,256 pysnmp: getNodeNameByOid: resolved :(1, 3, 6, 1, 2, 1, 3, 1, 1) -> ('iso', 'org', 'dod', 'internet', 'mgmt', 'mib-2', 'at', 'atTable', 'atEntry').()
2017-10-06 10:49:52,257 pysnmp: resolved indices are (Integer32(7), NetworkAddress().setComponentByPosition(0, IpAddress(hexValue='8ff801b1')))
1.3.6.1.2.1.3.1.1.1.7.1.143.248.1.177
2017-10-06 10:49:52,257 pysnmp: resolving 1.3.6.1.2.1.3.1.1.1.7.1.143.248.1.177 as OID or label
2017-10-06 10:49:52,257 pysnmp: getNodeNameByOid: resolved :1.3.6.1.2.1.3.1.1.1.7.1.143.248.1.177 -> ('iso', 'org', 'dod', 'internet', 'mgmt', 'mib-2', 'at', 'atTable', 'atEntry', 'atIfIndex').7.1.143.248.1.177
2017-10-06 10:49:52,257 pysnmp: resolved (ObjectName('1.3.6.1.2.1.3.1.1.1.7.1.143.248.1.177'),) into prefix ObjectName('1.3.6.1.2.1.3.1.1.1') and suffix ObjectName('7.1.143.248.1.177')
2017-10-06 10:49:52,257 pysnmp: getNodeNameByOid: resolved :1.3.6.1.2.1.3.1.1.1 -> ('iso', 'org', 'dod', 'internet', 'mgmt', 'mib-2', 'at', 'atTable', 'atEntry', 'atIfIndex').()
2017-10-06 10:49:52,257 pysnmp: resolved prefix ObjectName('1.3.6.1.2.1.3.1.1.1') into MIB node MibTableColumn((1, 3, 6, 1, 2, 1, 3, 1, 1, 1), Integer32())
2017-10-06 10:49:52,257 pysnmp: getNodeNameByOid: resolved :(1, 3, 6, 1, 2, 1, 3, 1, 1) -> ('iso', 'org', 'dod', 'internet', 'mgmt', 'mib-2', 'at', 'atTable', 'atEntry').()
2017-10-06 10:49:52,258 pysnmp: resolved indices are (Integer32(7), NetworkAddress().setComponentByPosition(0, IpAddress(hexValue='8ff801b1')))
('RFC1213-MIB', 'atIfIndex', (Integer32(7), NetworkAddress().setComponentByPosition(0, IpAddress(hexValue='8ff801b1'))))

Note:

• The atNetAddress of 143.248.1.177 is now correctly encoded as 1.143.248.1.177;
• A correctly formatted instance OID is now correctly decoded.

[astralblue]

That was the original design, then it occurred to me that there may be other Choice-based index types which will require similar cloning logic.

However, after seeing that SNMPv2-SMI now allows only simple-type indices, I agree that we don’t need to clutter PyASN1 anticipating something that is already disallowed by the RFC. 😃

I’ll update this PR to revert to the original version. Please disregard the PyASN1 PR.

[etingof]

Merged