Re: [JSch-users] Deadlock in KnownHosts

[Lothar K. <jo...@ki...>]

Hi,

Am 10.02.2016 um 09:38 schrieb Vladimir Kvashin:

> - does jsch accept contributions? if yes, I can try fixing this
> and propose a patch

I asked this question as well in the past and have never
received an answer.

> - are there any plans to fix it?

FWIW, here is a patch, that should fix the issue. The
Digester instance in KnownHost is used in a global way
and needed quite some synchronization. I changed it to
a new instance every time the digester is retrieved,
making the synchronization as a whole unnecessary.


Cheers, Lothar


--------------- snip
### Eclipse Workspace Patch 1.0
#P JSCH_EBD
Index: src/main/java/com/jcraft/jsch/KnownHosts.java
===================================================================
--- src/main/java/com/jcraft/jsch/KnownHosts.java	(revision 24760)
+++ src/main/java/com/jcraft/jsch/KnownHosts.java	(working copy)
@@ -39,7 +39,7 @@
   private String known_hosts=null;
   private java.util.Vector pool=null;

-  private MAC hmacsha1=null;
+  private Class hmacsha1_class = null;

   KnownHosts(JSch jsch){
     super();
@@ -482,17 +482,18 @@
     return hosts;
   }

-  private synchronized MAC getHMACSHA1(){
-    if(hmacsha1==null){
+  private MAC getHMACSHA1(){
       try{
-        Class c=Class.forName(jsch.getConfig("hmac-sha1"));
-        hmacsha1=(MAC)(c.newInstance());
+          if (hmacsha1_class == null){
+              String hmacsha1_classname = JSch.getConfig("hmac-sha1");
+              hmacsha1_class = Class.forName(hmacsha1_classname);
+          }
+          return (MAC) hmacsha1_class.newInstance();
       }
       catch(Exception e){
         System.err.println("hmacsha1: "+e);
       }
-    }
-    return hmacsha1;
+      return null;
   }

   HostKey createHashedHostKey(String host, byte[]key) throws JSchException {
@@ -539,14 +540,12 @@
       }
       MAC macsha1=getHMACSHA1();
       try{
-        synchronized(macsha1){
           macsha1.init(salt);
           byte[] foo=Util.str2byte(_host);
           macsha1.update(foo, 0, foo.length);
           byte[] bar=new byte[macsha1.getBlockSize()];
           macsha1.doFinal(bar, 0);
           return Util.array_equals(hash, bar);
-        }
       }
       catch(Exception e){
         System.out.println(e);
@@ -570,13 +569,11 @@
         }
       }
       try{
-        synchronized(macsha1){
           macsha1.init(salt);
           byte[] foo=Util.str2byte(host);
           macsha1.update(foo, 0, foo.length);
           hash=new byte[macsha1.getBlockSize()];
           macsha1.doFinal(hash, 0);
-        }
       }
       catch(Exception e){
       }
--------------- snip