Tolerate non-initialised entries in SNMP community table (#195)

It can happen that SNMP community table contains uninitialized entries.
These entries may stop internal SNMP community table indexing which
is done in rfc2576 to speed up SNMP engine operations when SNMPv1/v2c
is involved. Once a bad entry gets into SNMP community table, all
the rest queries would start failing.

This patch ignores incomplete SNMP community table entries in the
course of building indices.

1 files changed, 75 insertions, 25 deletions

diff --git a/pysnmp/proto/secmod/rfc2576.py b/pysnmp/proto/secmod/rfc2576.py
index 047974e0..f7947d97 100644
--- a/pysnmp/proto/secmod/rfc2576.py
+++ b/pysnmp/proto/secmod/rfc2576.py
@@ -38,7 +38,7 @@ class SnmpV1SecurityModel(base.AbstractSecurityModel):
 
             nextMibNode = snmpTargetParamsSecurityName
 
-            while 1:
+            while True:
                 try:
                     nextMibNode = snmpTargetParamsSecurityName.getNextNode(nextMibNode.name)
 
@@ -49,10 +49,18 @@ class SnmpV1SecurityModel(base.AbstractSecurityModel):
 
                 mibNode = snmpTargetParamsSecurityModel.getNode(snmpTargetParamsSecurityModel.name + instId)
 
-                if mibNode.syntax not in self.__nameToModelMap:
-                    self.__nameToModelMap[nextMibNode.syntax] = set()
+                try:
+                    if mibNode.syntax not in self.__nameToModelMap:
+                        self.__nameToModelMap[nextMibNode.syntax] = set()
+
+                    self.__nameToModelMap[nextMibNode.syntax].add(mibNode.syntax)
 
-                self.__nameToModelMap[nextMibNode.syntax].add(mibNode.syntax)
+                except PyAsn1Error:
+                    debug.logger & debug.flagSM and debug.logger(
+                        '_sec2com: table entries %r/%r hashing failed' % (
+                            nextMibNode.syntax, mibNode.syntax)
+                    )
+                    continue
 
             self.__paramsBranchId = snmpTargetParamsSecurityName.branchVersionId
 
@@ -72,7 +80,8 @@ class SnmpV1SecurityModel(base.AbstractSecurityModel):
             self.__securityMap = {}
 
             nextMibNode = snmpCommunityName
-            while 1:
+
+            while True:
                 try:
                     nextMibNode = snmpCommunityName.getNextNode(nextMibNode.name)
 
@@ -88,9 +97,17 @@ class SnmpV1SecurityModel(base.AbstractSecurityModel):
 
                 _contextName = snmpCommunityContextName.getNode(snmpCommunityContextName.name + instId).syntax
 
-                self.__securityMap[(_securityName,
-                                    _contextEngineId,
-                                    _contextName)] = nextMibNode.syntax
+                try:
+                    self.__securityMap[(_securityName,
+                                        _contextEngineId,
+                                        _contextName)] = nextMibNode.syntax
+
+                except PyAsn1Error:
+                    debug.logger & debug.flagSM and debug.logger(
+                        '_sec2com: table entries %r/%r/%r hashing failed' % (
+                            _securityName, _contextEngineId, _contextName)
+                    )
+                    continue
 
             self.__securityBranchId = snmpCommunityName.branchVersionId
 
@@ -123,11 +140,14 @@ class SnmpV1SecurityModel(base.AbstractSecurityModel):
             self.__transportToTagMap = {}
 
             nextMibNode = snmpTargetAddrTagList
+
             while True:
                 try:
                     nextMibNode = snmpTargetAddrTagList.getNextNode(nextMibNode.name)
+
                 except NoSuchInstanceError:
                     break
+
                 instId = nextMibNode.name[len(snmpTargetAddrTagList.name):]
                 targetAddrTDomain = snmpTargetAddrTDomain.getNode(snmpTargetAddrTDomain.name + instId).syntax
                 targetAddrTAddress = snmpTargetAddrTAddress.getNode(snmpTargetAddrTAddress.name + instId).syntax
@@ -142,17 +162,29 @@ class SnmpV1SecurityModel(base.AbstractSecurityModel):
                     TransportAddressIPv6, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols(
                         'TRANSPORT-ADDRESS-MIB', 'TransportAddressIPv6')
                     targetAddrTAddress = tuple(TransportAddressIPv6(targetAddrTAddress))
+
                 targetAddr = targetAddrTDomain, targetAddrTAddress
                 targetAddrTagList = snmpTargetAddrTagList.getNode(snmpTargetAddrTagList.name + instId).syntax
+
                 if targetAddr not in self.__transportToTagMap:
                     self.__transportToTagMap[targetAddr] = set()
-                if targetAddrTagList:
-                    self.__transportToTagMap[targetAddr].update(
-                        [SnmpTagValue(x)
-                         for x in targetAddrTagList.asOctets().split()]
+
+                try:
+                    if targetAddrTagList:
+                        self.__transportToTagMap[targetAddr].update(
+                            [SnmpTagValue(x)
+                             for x in targetAddrTagList.asOctets().split()]
+                        )
+
+                    else:
+                        self.__transportToTagMap[targetAddr].add(self.__emptyTag)
+
+                except PyAsn1Error:
+                    debug.logger & debug.flagSM and debug.logger(
+                        '_com2sec: table entries %r/%r hashing failed' % (
+                            targetAddr, targetAddrTagList)
                     )
-                else:
-                    self.__transportToTagMap[targetAddr].add(self.__emptyTag)
+                    continue
 
             self.__transportBranchId = snmpTargetAddrTAddress.branchVersionId
 
@@ -161,6 +193,7 @@ class SnmpV1SecurityModel(base.AbstractSecurityModel):
 
         snmpTargetParamsSecurityName, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols(
             'SNMP-TARGET-MIB', 'snmpTargetParamsSecurityName')
+
         if self.__paramsBranchId != snmpTargetParamsSecurityName.branchVersionId:
             snmpTargetParamsSecurityModel, = snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols(
                 'SNMP-TARGET-MIB', 'snmpTargetParamsSecurityModel')
@@ -180,10 +213,18 @@ class SnmpV1SecurityModel(base.AbstractSecurityModel):
 
                 mibNode = snmpTargetParamsSecurityModel.getNode(snmpTargetParamsSecurityModel.name + instId)
 
-                if nextMibNode.syntax not in self.__nameToModelMap:
-                    self.__nameToModelMap[nextMibNode.syntax] = set()
+                try:
+                    if nextMibNode.syntax not in self.__nameToModelMap:
+                        self.__nameToModelMap[nextMibNode.syntax] = set()
+
+                    self.__nameToModelMap[nextMibNode.syntax].add(mibNode.syntax)
 
-                self.__nameToModelMap[nextMibNode.syntax].add(mibNode.syntax)
+                except PyAsn1Error:
+                    debug.logger & debug.flagSM and debug.logger(
+                        '_com2sec: table entries %r/%r hashing failed' % (
+                            nextMibNode.syntax, mibNode.syntax)
+                    )
+                    continue
 
             self.__paramsBranchId = snmpTargetParamsSecurityName.branchVersionId
 
@@ -209,6 +250,7 @@ class SnmpV1SecurityModel(base.AbstractSecurityModel):
             self.__tagAndCommunityToSecurityMap = {}
 
             nextMibNode = snmpCommunityName
+
             while True:
                 try:
                     nextMibNode = snmpCommunityName.getNextNode(nextMibNode.name)
@@ -229,17 +271,25 @@ class SnmpV1SecurityModel(base.AbstractSecurityModel):
 
                 _tagAndCommunity = transportTag, nextMibNode.syntax
 
-                if _tagAndCommunity not in self.__tagAndCommunityToSecurityMap:
-                    self.__tagAndCommunityToSecurityMap[_tagAndCommunity] = set()
+                try:
+                    if _tagAndCommunity not in self.__tagAndCommunityToSecurityMap:
+                        self.__tagAndCommunityToSecurityMap[_tagAndCommunity] = set()
 
-                self.__tagAndCommunityToSecurityMap[_tagAndCommunity].add(
-                    (securityName, contextEngineId, contextName)
-                )
+                    self.__tagAndCommunityToSecurityMap[_tagAndCommunity].add(
+                        (securityName, contextEngineId, contextName)
+                    )
+
+                    if nextMibNode.syntax not in self.__communityToTagMap:
+                        self.__communityToTagMap[nextMibNode.syntax] = set()
 
-                if nextMibNode.syntax not in self.__communityToTagMap:
-                    self.__communityToTagMap[nextMibNode.syntax] = set()
+                    self.__communityToTagMap[nextMibNode.syntax].add(transportTag)
 
-                self.__communityToTagMap[nextMibNode.syntax].add(transportTag)
+                except PyAsn1Error:
+                    debug.logger & debug.flagSM and debug.logger(
+                        '_com2sec: table entries %r/%r hashing failed' % (
+                            _tagAndCommunity, nextMibNode.syntax)
+                    )
+                    continue
 
             self.__communityBranchId = snmpCommunityName.branchVersionId