[HDFS-14285] libhdfs hdfsRead copies entire array even if its only partially filled

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 3.3.0
• Component/s: hdfs-client, libhdfs, native
• Assignee: Sahil Takiar
• Reporter: Sahil Takiar
• Created: 15/Feb/19 22:18
• Updated: 02/Oct/19 17:15
• Resolved: 23/Feb/19 01:55

Description

There is a bug in libhdfs hdfsRead

    jthr = invokeMethod(env, &jVal, INSTANCE, jInputStream, HADOOP_ISTRM,
                               "read", "([B)I", jbRarray);
    if (jthr) {
        destroyLocalReference(env, jbRarray);
        errno = printExceptionAndFree(env, jthr, PRINT_EXC_ALL,
            "hdfsRead: FSDataInputStream#read");
        return -1;
    }
    if (jVal.i < 0) {
        // EOF
        destroyLocalReference(env, jbRarray);
        return 0;
    } else if (jVal.i == 0) {
        destroyLocalReference(env, jbRarray);
        errno = EINTR;
        return -1;
    }
    (*env)->GetByteArrayRegion(env, jbRarray, 0, noReadBytes, buffer);

The method makes a call to FSInputStream#read(byte[]) to fill in the Java byte array, however, #read(byte[]) is not guaranteed to fill up the entire array, instead it returns the number of bytes written to the array (which could be less than the size of the array). Yet `GetByteArrayRegion decides to copy the entire contents of the jbArray into the buffer (noReadBytes is initialized to the length of the buffer and is never updated). So if FSInputStream#read(byte[]) decides to read less data than the size of the byte array, the call to GetByteArrayRegion will essentially copy more bytes than necessary.