# View-based Access Control Model
from pysnmp.smi.error import NoSuchObjectError
from pysnmp.proto import error
from pysnmp import debug
accessModelID = 3
__powOfTwoSeq = [128, 64, 32, 16, 8, 4, 2, 1]
# 3.2
def isAccessAllowed(
snmpEngine,
securityModel,
securityName,
securityLevel,
viewType,
contextName,
variableName):
mibInstrumController = snmpEngine.msgAndPduDsp.mibInstrumController
debug.logger & debug.flagACL and debug.logger('isAccessAllowed: viewType %s for variableName %s' % (viewType, variableName))
# 3.2.1
vacmContextEntry, = mibInstrumController.mibBuilder.importSymbols('SNMP-VIEW-BASED-ACM-MIB', 'vacmContextEntry')
tblIdx = vacmContextEntry.getInstIdFromIndices(contextName)
try:
vacmContextName = vacmContextEntry.getNode(
vacmContextEntry.name + (1,) + tblIdx
).syntax
except NoSuchObjectError:
raise error.StatusInformation(errorIndication='noSuchContext')
# 3.2.2
vacmSecurityToGroupEntry, = mibInstrumController.mibBuilder.importSymbols(
'SNMP-VIEW-BASED-ACM-MIB', 'vacmSecurityToGroupEntry'
)
tblIdx = vacmSecurityToGroupEntry.getInstIdFromIndices(
securityModel, securityName
)
try:
vacmGroupName = vacmSecurityToGroupEntry.getNode(
vacmSecurityToGroupEntry.name + (3,) + tblIdx
).syntax
except NoSuchObjectError:
raise error.StatusInformation(errorIndication='noGroupName')
# 3.2.3
vacmAccessEntry, = mibInstrumController.mibBuilder.importSymbols(
'SNMP-VIEW-BASED-ACM-MIB', 'vacmAccessEntry'
)
# XXX partial context name match
tblIdx = vacmAccessEntry.getInstIdFromIndices(
vacmGroupName, contextName, securityModel, securityLevel
)
# 3.2.4
if viewType == 'read':
entryIdx = vacmAccessEntry.name + (5,) + tblIdx
elif viewType == 'write':
entryIdx = vacmAccessEntry.name + (6,) + tblIdx
elif viewType == 'notify':
entryIdx = vacmAccessEntry.name + (7,) + tblIdx
else:
raise error.ProtocolError('Unknown view type %s' % viewType)
try:
viewName = vacmAccessEntry.getNode(entryIdx).syntax
except NoSuchObjectError:
raise error.StatusInformation(errorIndication='noAccessEntry')
if not len(viewName):
raise error.StatusInformation(errorIndication='noSuchView')
# XXX split onto object & instance ?
# 3.2.5a
vacmViewTreeFamilyEntry, = mibInstrumController.mibBuilder.importSymbols('SNMP-VIEW-BASED-ACM-MIB', 'vacmViewTreeFamilyEntry')
tblIdx = vacmViewTreeFamilyEntry.getInstIdFromIndices(viewName)
# Walk over entries
initialTreeName = treeName = vacmViewTreeFamilyEntry.name + (2,) + tblIdx
maskName = vacmViewTreeFamilyEntry.name + (3,) + tblIdx
while 1:
vacmViewTreeFamilySubtree = vacmViewTreeFamilyEntry.getNextNode(
treeName
)
vacmViewTreeFamilyMask = vacmViewTreeFamilyEntry.getNextNode(
maskName
)
treeName = vacmViewTreeFamilySubtree.name
maskName = vacmViewTreeFamilyMask.name
if initialTreeName != treeName[:len(initialTreeName)]:
# 3.2.5b
raise error.StatusInformation(errorIndication='notInView')
l = len(vacmViewTreeFamilySubtree.syntax)
if l > len(variableName):
continue
if vacmViewTreeFamilyMask.syntax:
mask = []
for c in map(None, str(vacmViewTreeFamilyMask.syntax)):
mask = mask + map(lambda b,c=ord(c): b&c, __powOfTwoSeq)
m = len(mask)-1
idx = l-1
while idx:
if idx > m or mask[idx] and \
vacmViewTreeFamilySubtree.syntax[idx] != variableName[idx]:
break
idx = idx - 1
if idx: continue # no match
else: # no mask
if vacmViewTreeFamilySubtree.syntax != variableName[:l]:
continue # no match
# 3.2.5c
return error.StatusInformation(errorIndication='accessAllowed')
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