#265 change buffer_margin computation to be dynamic based upon the MA…

…C to allow connections that advertise small maximum packet sizes.

pom.xml

@@ -163,6 +163,12 @@
             <version>1.15</version>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>com.google.guava</groupId>
+            <artifactId>guava</artifactId>
+            <version>31.1-jre</version>
+            <scope>test</scope>
+        </dependency>
         <dependency>
             <groupId>org.apache.logging.log4j</groupId>
             <artifactId>log4j-core</artifactId>

src/main/java/com/jcraft/jsch/Buffer.java

@@ -212,8 +212,13 @@ byte getCommand(){
     return buffer[5];
   }
 
+  // Hardcode this since we can't use dynamic Session value
+  private static final int buffer_margin = 32 + // maximum padding length
+                                           64 + // maximum mac length
+                                           32;  // margin for deflater; deflater may inflate data
+
   void checkFreeSize(int n){
-    int size = index+n+Session.buffer_margin;
+    int size = index+n+buffer_margin;
     if(buffer.length<size){
       int i = buffer.length*2;
       if(i<size) i = size;

src/main/java/com/jcraft/jsch/Channel.java

@@ -240,10 +240,15 @@ private synchronized void init() throws IOException{
           packet=new Packet(buffer);
 
           byte[] _buf=buffer.buffer;
-          if(_buf.length-(14+0)-Session.buffer_margin<=0){
-            buffer=null;
-            packet=null;
-            throw new IOException("failed to initialize the channel.");
+          try{
+            if(_buf.length-(14+0)-getSession().getBufferMargin()<=0){
+              buffer=null;
+              packet=null;
+              throw new IOException("failed to initialize the channel.");
+            }
+          }
+          catch(JSchException e){
+            throw new IOException("failed to initialize the channel.", e);
           }
 
         }
@@ -265,21 +270,27 @@ public void write(byte[] buf, int s, int l) throws IOException{
 
           byte[] _buf=buffer.buffer;
           int _bufl=_buf.length;
-          while(l>0){
-            int _l=l;
-            if(l>_bufl-(14+dataLen)-Session.buffer_margin){
-              _l=_bufl-(14+dataLen)-Session.buffer_margin;
-            }
-
-            if(_l<=0){
-              flush();
-              continue;
+          try{
+            while(l>0){
+              int _l=l;
+              int buffer_margin=getSession().getBufferMargin();
+              if(l>_bufl-(14+dataLen)-buffer_margin){
+                _l=_bufl-(14+dataLen)-buffer_margin;
+              }
+
+              if(_l<=0){
+                flush();
+                continue;
+              }
+
+              System.arraycopy(buf, s, _buf, 14+dataLen, _l);
+              dataLen+=_l;
+              s+=_l;
+              l-=_l;
             }
-
-            System.arraycopy(buf, s, _buf, 14+dataLen, _l);
-            dataLen+=_l;
-            s+=_l;
-            l-=_l;
+          }
+          catch(JSchException e){
+            throw new IOException(e.toString(), e);
           }
         }
 

src/main/java/com/jcraft/jsch/ChannelDirectStreamLocal.java

@@ -47,7 +47,7 @@ protected Packet genChannelOpenPacket() {
 
         Buffer buf = new Buffer(50 +
                 socketPath.length() +
-                Session.buffer_margin);
+                session.getBufferMargin());
         Packet packet = new Packet(buf);
         packet.reset();
         buf.putByte((byte) SSH_MSG_CHANNEL_OPEN);

src/main/java/com/jcraft/jsch/ChannelDirectTCPIP.java

@@ -104,7 +104,7 @@ void run(){
         i=io.in.read(buf.buffer, 
                      14, 
                      buf.buffer.length-14
-                     -Session.buffer_margin
+                     -_session.getBufferMargin()
                      );
         if(i<=0){
           eof();
@@ -154,7 +154,7 @@ public void setOutputStream(OutputStream out){
   protected Packet genChannelOpenPacket(){
     Buffer buf = new Buffer(50 + // 6 + 4*8 + 12
                             host.length() + originator_IP_address.length() +
-                            Session.buffer_margin);
+                            session.getBufferMargin());
     Packet packet = new Packet(buf);
     // byte   SSH_MSG_CHANNEL_OPEN(90)
     // string channel type         //

src/main/java/com/jcraft/jsch/ChannelForwardedTCPIP.java

@@ -96,14 +96,14 @@ public void run(){
     Packet packet=new Packet(buf);
     int i=0;
     try{
-      Session _session = getSession();
+      Session _session=getSession();
       while(thread!=null && 
             io!=null && 
             io.in!=null){
         i=io.in.read(buf.buffer, 
                      14, 
                      buf.buffer.length-14
-                     -Session.buffer_margin
+                     -_session.getBufferMargin()
                      );
         if(i<=0){
           eof();

src/main/java/com/jcraft/jsch/ChannelSession.java

@@ -241,14 +241,15 @@ void run(){
     Packet packet=new Packet(buf);
     int i=-1;
     try{
+      Session _session=getSession();
       while(isConnected() &&
             thread!=null && 
             io!=null && 
             io.in!=null){
         i=io.in.read(buf.buffer, 
                      14,    
                      buf.buffer.length-14
-                     -Session.buffer_margin
+                     -_session.getBufferMargin()
                      );
         if(i==0)continue;
         if(i==-1){
@@ -262,7 +263,7 @@ void run(){
         buf.putInt(recipient);
         buf.putInt(i);
         buf.skip(i);
-        getSession().write(packet, this, i);
+        _session.write(packet, this, i);
       }
     }
     catch(Exception e){

src/main/java/com/jcraft/jsch/ChannelSftp.java

@@ -593,9 +593,10 @@ public void _put(InputStream src, String dst,
 
       boolean dontcopy=true;
 
+      int buffer_margin=session.getBufferMargin();
       if(!dontcopy){  // This case will not work anymore.
         data=new byte[obuf.buffer.length
-                      -(5+13+21+handle.length+Session.buffer_margin
+                      -(5+13+21+handle.length+buffer_margin
                         )
         ];
       }
@@ -616,7 +617,7 @@ public void _put(InputStream src, String dst,
       else{
         data=obuf.buffer;
         _s=5+13+21+handle.length;
-        _datalen=obuf.buffer.length-_s-Session.buffer_margin;
+        _datalen=obuf.buffer.length-_s-buffer_margin;
       }
 
       int bulk_requests = rq.size();
@@ -664,7 +665,7 @@ public void _put(InputStream src, String dst,
             foo-=sendWRITE(handle, offset, data, 0, foo);
             if(data!=obuf.buffer){
               data=obuf.buffer;
-              _datalen=obuf.buffer.length-_s-Session.buffer_margin;
+              _datalen=obuf.buffer.length-_s-buffer_margin;
             }
           }
           else {
@@ -2581,8 +2582,10 @@ private int sendWRITE(byte[] handle, long offset,
                         byte[] data, int start, int length) throws Exception{
     int _length=length;
     opacket.reset();
-    if(obuf.buffer.length<obuf.index+13+21+handle.length+length+Session.buffer_margin){
-      _length=obuf.buffer.length-(obuf.index+13+21+handle.length+Session.buffer_margin);
+    Session _session=getSession();
+    int buffer_margin=_session.getBufferMargin();
+    if(obuf.buffer.length<obuf.index+13+21+handle.length+length+buffer_margin){
+      _length=obuf.buffer.length-(obuf.index+13+21+handle.length+buffer_margin);
       // System.err.println("_length="+_length+" length="+length);
     }
 
@@ -2597,7 +2600,7 @@ private int sendWRITE(byte[] handle, long offset,
       obuf.putInt(_length);
       obuf.skip(_length);
     }
-    getSession().write(opacket, this, 21+handle.length+_length+4);
+    _session.write(opacket, this, 21+handle.length+_length+4);
     return _length;
   }
   private void sendREAD(byte[] handle, long offset, int length) throws Exception{

src/main/java/com/jcraft/jsch/ChannelX11.java

@@ -155,12 +155,13 @@ void run(){
     Packet packet=new Packet(buf);
     int i=0;
     try{
+      Session _session=getSession();
       while(thread!=null &&
             io!=null &&
             io.in!=null){
         i=io.in.read(buf.buffer, 
                      14, 
-                     buf.buffer.length-14-Session.buffer_margin);
+                     buf.buffer.length-14-_session.getBufferMargin());
         if(i<=0){
           eof();
           break;
@@ -171,7 +172,7 @@ void run(){
         buf.putInt(recipient);
         buf.putInt(i);
         buf.skip(i);
-        getSession().write(packet, this, i);
+        _session.write(packet, this, i);
       }
     }
     catch(Exception e){

src/main/java/com/jcraft/jsch/Session.java

@@ -135,10 +135,6 @@ public class Session{
 
   SocketFactory socket_factory=null;
 
-  static final int buffer_margin = 32 + // maximum padding length
-                                   64 + // maximum mac length
-                                   32;  // margin for deflater; deflater may inflate data
-
   private Hashtable<String, String> config=null;
 
   private Proxy proxy=null;
@@ -562,7 +558,7 @@ public void connect(int connectTimeout) throws JSchException{
         if(isConnected){
           String message = e.toString();
           packet.reset();
-          buf.checkFreeSize(1+4*3+message.length()+2+buffer_margin);
+          buf.checkFreeSize(1+4*3+message.length()+2+getBufferMargin());
           buf.putByte((byte)SSH_MSG_DISCONNECT);
           buf.putInt(3);
           buf.putString(Util.str2byte(message));
@@ -3287,4 +3283,27 @@ public Logger getLogger() {
   public void setLogger(Logger logger) {
     this.logger = logger;
   }
+
+  int getBufferMargin() {
+    int buffer_margin = 32 + // maximum padding length
+                        32;  // margin for deflater; deflater may inflate data
+
+    Cipher _c2scipher = c2scipher;
+    MAC _c2smac = c2smac;
+
+    // maximum mac length
+    int mac_length = 20;
+    if (_c2scipher != null && (_c2scipher.isChaCha20() || _c2scipher.isAEAD())) {
+      if (_c2scipher.getTagSize() > mac_length) {
+        mac_length = _c2scipher.getTagSize();
+      }
+    } else if (_c2smac != null) {
+      if (_c2smac.getBlockSize() > mac_length) {
+        mac_length = _c2smac.getBlockSize();
+      }
+    }
+    buffer_margin += mac_length;
+
+    return buffer_margin;
+  }
 }