First let me say that PySNMP is pretty handy, it has made my life a lot
easier in the last few weeks.
Secondly, in doing some development and testing of my manager side
application I think I hit a bug in pysnmp/v4/proto/secmod/rfc2576.py
SnmpV1SecurityModel.processIncomingMsg. Apologies in advance if I am just
misunderstanding this.
There is a while(1) look in there that is exited with a break when the
incoming communityName is matched against an entry in the SNMP-COMMUNITY-MIB
snmpCommunityName or we exhaust all the snmpCommunityName entries without
finding a match, in which case the request should be dropped and
snmpInBadCommunityNames incremented.
The problem is we always seem to allow in the user, even when a match is not
found. The problem is that the 'else' clause outside of the while(1) loop
can never be entered since the else clause on a loop is only entered when
the loop terminates normally, which is impossible for a while(1) loop.
>From the python docs:
"Loop statements may have an else clause; it is executed when the loop
terminates through exhaustion of the list (with for) or when the condition
becomes false (with while), but not when the loop is terminated by a
breakstatement."
while 1:
try:
mibNodeIdx = snmpCommunityName.getNextNode(
mibNodeIdx.name
)
except NoSuchInstanceError:
break
if mibNodeIdx.syntax != communityName:
continue
break
else:
# I don't think we can ever get here!
snmpInBadCommunityNames, =
snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols('__SNMP-COMMUNITY-MIB',
'snmpInBadCommunityNames')
snmpInBadCommunityNames.syntax =
snmpInBadCommunityNames.syntax+1
raise error.StatusInformation(
errorIndication = 'unknownCommunityName'
)
I think instead we want something like this, although a better solution is
welcome:
while 1:
try:
mibNodeIdx = snmpCommunityName.getNextNode(
mibNodeIdx.name
)
except NoSuchInstanceError:
print 'unknownCommunityName: %s' % (communityName,)
snmpInBadCommunityNames, =
snmpEngine.msgAndPduDsp.mibInstrumController.mibBuilder.importSymbols('__SNMPv2-MIB',
'snmpInBadCommunityNames')
snmpInBadCommunityNames.syntax =
snmpInBadCommunityNames.syntax+1
raise error.StatusInformation(
errorIndication = 'unknownCommunityName'
)
break # i guess this break isn't needed
if mibNodeIdx.syntax != communityName:
continue
break
Thanks in advance for any replies, and keep up the good work.
-Paul Warner
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