From: michalkurka <michalk@h2o.ai>
Date: Wed, 17 Mar 2021 17:12:21 +0000 (-0400)
Subject: Fix a race condition in CtClassType#getClassFile3
X-Git-Tag: rel_3_28_0_ga~6^2
X-Git-Url: https://source.dussan.org/?a=commitdiff_plain;h=refs%2Fpull%2F363%2Fhead;p=javassist.git

Fix a race condition in CtClassType#getClassFile3

javassist fails to find a class when concurrently running process
compresses the class (converts classfile to raw bytes)

the idea of the fix is to make sure to only update rawClassfile and classfile
under lock in getClassFile3, all other places that modify classfile are
already synchronized

when reading the object state, we need to read under lock both classfile and
rawClassFile otherwise we might get an inconsistent state
---

diff --git a/src/main/javassist/CtClassType.java b/src/main/javassist/CtClassType.java
index ae196c4a..959ec302 100644
--- a/src/main/javassist/CtClassType.java
+++ b/src/main/javassist/CtClassType.java
@@ -179,6 +179,7 @@ class CtClassType extends CtClass {
     }
 
     public ClassFile getClassFile3(boolean doCompress) {
+        // quick path - no locking
         ClassFile cfile = classfile;
         if (cfile != null)
             return cfile;
@@ -186,17 +187,29 @@ class CtClassType extends CtClass {
         if (doCompress)
             classPool.compress();
 
-        if (rawClassfile != null) {
+        byte[] rcfile;
+        synchronized (this) {
+            // repeat under lock to make sure we get a consistent result (classfile might have been set by another thread)
+            cfile = classfile;
+            if (cfile != null)
+                return cfile;
+
+            rcfile = rawClassfile;
+        }
+
+        if (rcfile != null) {
+            final ClassFile cf;
             try {
-                ClassFile cf = new ClassFile(new DataInputStream(
-                                             new ByteArrayInputStream(rawClassfile)));
-                rawClassfile = null;
-                getCount = GET_THRESHOLD;
-                return setClassFile(cf);
+                cf = new ClassFile(new DataInputStream(new ByteArrayInputStream(rcfile)));
             }
             catch (IOException e) {
                 throw new RuntimeException(e.toString(), e);
             }
+            getCount = GET_THRESHOLD;
+            synchronized (this) {
+                rawClassfile = null;
+                return setClassFile(cf);
+            }
         }
 
         InputStream fin = null;