[SNMP4J] Problems in DefaultTcpTransportMapping when receiving fragmented header
Frank Fock
fock at agentpp.com
Tue Jan 26 01:39:08 CET 2016
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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