[SNMP4J] [PATCH] Workaround for Net-SNMP < 5.4.1 64-bit agent bug

[Frank Fock]

Hi Jeff,

I have noticed your patch and thought about how the
interoperability issue could be solved best.
Since the bug is on the NET-SNMP side, I do not
would like to spent any CPU cycles for a workaround
for this bug in SNMP4J.

Registering your own IpAddress subclass via the
smisynaxes.properties could be a clean solution.
You could name the class IpAddressNETSNMP64bitBugAware
and implement your patch there.

Let me know if you have any difficulties implementing/using
such a mechanism.

Best regards,
Frank

Jeff Gehlbach schrieb:
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>
> Hi!
>
> Replying to my own post, very bad form I know, but I've received no 
> feedback on this patch.
>
> Frank, do you think this is something that could be integrated into a 
> future release?  In a perfect world we'd just tell everyone to use an 
> agent that doesn't exhibit this bug, but the bug is widespread and not 
> widely understood -- most users assume that the bug is in OpenNMS 
> since they can walk the agent just fine using the Net-SNMP tools.  
> This simple change to Snmp4J alleviates a LOT of heartburn.  Having it 
> in the official code base means that the OpenNMS project doesn't need 
> to maintain a patched version of Snmp4J, and other projects that use 
> Snmp4J will reap the benefits as well.
>
> Thanks for your consideration,
> - -jeff
>
>
> On 09Oct , 2007, at 8:59 AM, Jeff Gehlbach wrote:
>
>> Hi!
>>
>> I work on the OpenNMS project, which has for some time been using 
>> SNMP4J as its default protocol implementation.  Thank you for the 
>> fabulous work on SNMP4J!
>>
>> I'm writing to propose a patch that works around a bounds-checking 
>> bug in the Net-SNMP project's BER library that causes OpenNMS to fail 
>> to discover any 64-bit host running a Net-SNMP snmpd older than 
>> version 5.4.1.  The BER bug in question causes IPv4 addresses to be 
>> encoded as 64-bit values but marked in the PDU as being four bytes 
>> long.  When SNMP4J decodes a RESPONSE PDU containing such a value, it 
>> correctly discards the variable in question.  The upshot is that 
>> OpenNMS cannot discover the interfaces on a node because it does not 
>> get a valid picture of the node's ipAddrTable.
>>
>> The following patch, against Snmp4J 1.8.2, seems to effect a 
>> workaround for this highly annoying and destructive agent bug.  I 
>> (and several others) have successfully discovered and managed hosts 
>> exhibiting this agent bug by dropping in an SNMP4J JAR built from 
>> sources with this patch applied.  The addition of a property to 
>> enable this workaround seemed the simplest and least intrusive route, 
>> but I'm not married to the idea.  Feedback is earnestly solicited!
>>
>> Thanks,
>> - -jeff
>>
>>
>> diff -ur snmp4j-1.8.2.orig/src/org/snmp4j/smi/IpAddress.java 
>> snmp4j-1.8.2/src/org/snmp4j/smi/IpAddress.java
>> - --- snmp4j-1.8.2.orig/src/org/snmp4j/smi/IpAddress.java 2007-03-10 
>> 21:59:12.000000000 -0500
>> +++ snmp4j-1.8.2/src/org/snmp4j/smi/IpAddress.java      2007-08-26 
>> 19:07:26.000000000 -0400
>> @@ -150,9 +150,17 @@
>>                              type.getValue());
>>      }
>>      if (value.length != 4) {
>> - -      throw new IOException("IpAddress encoding error, wrong 
>> length: " +
>> +         if ( (value.length == 8) && 
>> (System.getProperty("org.snmp4j.smi.bugCompat.netSnmpIpAddress8Bytes").equals("true")) 
>> ) {
>> +               byte[] tempValue = { 0,0,0,0 };
>> +               for (int i = 0; i < 4; i++) {
>> +                 tempValue[i] = value[i];
>> +               }
>> +               value = tempValue;
>> +         } else {
>> +        throw new IOException("IpAddress encoding error, wrong 
>> length: " +
>>                              value.length);
>> - -    }
>> +      }
>> +       }
>>      inetAddress = InetAddress.getByAddress(value);
>>    }
>
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