[SNMP4J] Problems in DefaultTcpTransportMapping when receiving fragmented header
Frank Fock
fock at agentpp.com
Tue Jan 26 08:48:11 CET 2016
Ji Bruno,
Sorry for the typo in the salutation. It was probably too late :-)
Many thanks for your valuable feedback though. When I wrote the
initial version I could not image that the first 6 bytes of the TCP
message could get fragmented (because the size of the message
should have been determined in one go)!
You never stop learning ;-)
Best regards,
Frank
> On 26 Jan 2016, at 01:39, Frank Fock <fock at agentpp.com> wrote:
>
> Hi Michal,
>
> The latest 2.4.2 snapshot now contains the two fixes for the below described issues.
> However, for the second issue I implemented a different approach in order to
> optimize buffer usage and minimize buffer copy operations while making sure
> not more data is read then the (checked) message length determines.
>
> Best regards,
> Frank
>
> Am 25.01.2016 um 22:29 schrieb Bruno Filipe Basilio:
>>> I have fixed this issue in the latest SNMP4J 2.4.2 snapshot release.
>>> Your fix, seemed to be not complete (it covers not all kind of fragmentations).
>>> So I developed a more general fix.
>> Thank you for your input.
>> I've tested your fix and hit some other issues, see details bellow.
>> Please check the following changes that seem to fix the issues in our tested scenario.
>>
>> --- old/org/snmp4j/transport/DefaultTcpTransportMapping.java 2016-01-24 23:49:26.000000000 +0000
>> +++ new/org/snmp4j/transport/DefaultTcpTransportMapping.java 2016-01-25 20:26:28.671899400 +0000
>> @@ -524,14 +558,16 @@ public class DefaultTcpTransportMapping
>> public MessageLength getMessageLength(ByteBuffer buf) throws IOException {
>> MutableByte type = new MutableByte();
>> BERInputStream is = new BERInputStream(buf);
>> - int ml = BER.decodeHeader(is, type);
>> + int ml = BER.decodeHeader(is, type, false);
>> int hl = (int)is.getPosition();
>> MessageLength messageLength = new MessageLength(hl, ml);
>> return messageLength;
>> @@ -1199,14 +1241,17 @@ public class DefaultTcpTransportMapping
>>
>> private void addBufferToReadBuffer(SocketEntry entry, ByteBuffer byteBuffer) {
>> int buflen = byteBuffer.position();
>> + int buflimit = byteBuffer.limit();
>> if (entry.getReadBuffer() != null) {
>> entry.getReadBuffer().put(byteBuffer.array(), 0, buflen);
>> }
>> else {
>> - byte[] message = new byte[byteBuffer.limit()];
>> + byte[] message = new byte[byteBuffer.capacity()];
>> byteBuffer.flip();
>> byteBuffer.get(message, 0, buflen);
>> ByteBuffer newBuffer = ByteBuffer.wrap(message);
>> + newBuffer.limit(buflimit);
>> newBuffer.position(buflen);
>> entry.setReadBuffer(newBuffer);
>> }
>>
>> *Issue 1*: Message length decoding in header fails when checking message length
>> Logs:
>> 2016-01-25 09:42:38,324-0700 [DEBUG|DefaultTcpTransportMapping$ServerThread] (DefaultTcpTransportMapping.java:1034) Reading header 9 bytes from 172.26.50.120/4001
>> 2016-01-25 09:42:38,402-0700 [DEBUG|DefaultTcpTransportMapping$ServerThread] (DefaultTcpTransportMapping.java:1001) Read 1 bytes from 172.26.50.120/4001
>> 2016-01-25 09:42:38,402-0700 [WARN|DefaultTcpTransportMapping$ServerThread] (DefaultTcpTransportMapping.java:854) java.io.IOException: The encoded length 127 exceeds the number of bytes left in input at position 6 which actually is 10
>> 2016-01-25 09:42:38,402-0700 [DEBUG|TcpTransportMapping] (TcpTransportMapping.java:133) Firing transport state event: org.snmp4j.transport.TransportStateEvent[source=org.snmp4j.transport.DefaultTcpTransportMapping at 14aa6c3,peerAddress=172.26.50.120/4001,newState=2,cancelled=false,causingException=java.io.IOException: The encoded length 127 exceeds the number of bytes left in input at position 6 which actually is 10]
>>
>> *Issue 2*: Read buffer capacity definition fail after fixing issue 1
>> Logs:
>> 2016-01-25 12:13:15,480-0700 [DEBUG|DefaultTcpTransportMapping$ServerThread] (DefaultTcpTransportMapping.java:1034) Reading header 1 bytes from 172.26.50.120/4001
>> 2016-01-25 12:13:15,551-0700 [DEBUG|DefaultTcpTransportMapping$ServerThread] (DefaultTcpTransportMapping.java:1001) Read 9 bytes from 172.26.50.120/4001
>> 2016-01-25 12:13:15,551-0700 [DEBUG|DefaultTcpTransportMapping$ServerThread] (DefaultTcpTransportMapping.java:1074) Message length is org.snmp4j.transport.MessageLength[headerLength=6,payloadLength=130]
>>
>> std-out:
>> Exception in thread "DefaultTCPTransportMapping_10.170.0.12/0" java.lang.IllegalArgumentException
>> at java.nio.Buffer.limit(Buffer.java:267)
>> at org.snmp4j.transport.DefaultTcpTransportMapping$ServerThread.readSnmpMessagePayload(DefaultTcpTransportMapping.java:1092)
>> at org.snmp4j.transport.DefaultTcpTransportMapping$ServerThread.readMessage(DefaultTcpTransportMapping.java:1011)
>> at org.snmp4j.transport.DefaultTcpTransportMapping$ServerThread.run(DefaultTcpTransportMapping.java:838)
>> at java.lang.Thread.run(Thread.java:724)
>>
>> Best regards,
>> Bruno
>>
>>
>> Bruno Filipe Basílio
>> Departamento de Investigação, Desenvolvimento e Inovação
>>
>> Tel: (+351) 214233436
>>
>> http://www.brisainovacao.pt
>>
>>
>>
>>
>>
>>
>>
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