[jira] [Closed] (JAMES-2200) Potential undefined behavior in org.apache.james.mailrepository.file.MBoxMailRepository

["Tellier Benoit (JIRA)" <se...@james.apache.org>]

     [ https://issues.apache.org/jira/browse/JAMES-2200?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Tellier Benoit closed JAMES-2200.
---------------------------------
    Resolution: Won't Fix

Related code had been deprecated and removed

> Potential undefined behavior in org.apache.james.mailrepository.file.MBoxMailRepository
> ---------------------------------------------------------------------------------------
>
>                 Key: JAMES-2200
>                 URL: https://issues.apache.org/jira/browse/JAMES-2200
>             Project: James Server
>          Issue Type: Bug
>            Reporter: Daniel Trebbien
>            Priority: Major
>
> _This class is within the 'Apache James :: Server :: Data :: File Persistence' project._
> In the list() method, there is a line of code that potentially invokes undefined behavior. Around [line 577|https://github.com/apache/james-project/blob/bc995fc1e8324ef5adfbf3de329546a8e42125fb/server/data/data-file/src/main/java/org/apache/james/mailrepository/file/MBoxMailRepository.java#L577], the construction of {{keys}} can invoke undefined behavior because the ArrayList constructor that is invoked iterates over the given collection (see [https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html#ArrayList-java.util.Collection-]), and the [documentation for Hashtable.keySet()|https://docs.oracle.com/javase/8/docs/api/java/util/Hashtable.html#keySet--] states:
> {quote}
> If the map is modified while an iteration over the set is in progress (except through the iterator's own remove operation), the results of the iteration are undefined.
> {quote}
> In the case where the {{mList}} Hashtable is modified while another thread is within list() making a copy of the key set, this invokes undefined behavior.
> One way of fixing this particular issue is to manually synchronize on {{mList}} while {{keys}} is being constructed (although, this is technically not covered in the documentation, so the fix of manually synching on {{mList}} would be relying on the specifics of a particular implementation; it _would_ be guaranteed if Collections.synchronizedMap() were used instead).
> However, there are other thread safety issues in the form of unsynchronized access to the {{mList}} and {{mboxFile}} fields. Some threads might be setting these fields to different values while other threads are trying to read them.
> To illustrate my concern, consider the following scenario: One thread is within selectMessage() around [line 415|https://github.com/apache/james-project/blob/bc995fc1e8324ef5adfbf3de329546a8e42125fb/server/data/data-file/src/main/java/org/apache/james/mailrepository/file/MBoxMailRepository.java#L415]. The thread retrieves the current value of field {{mList}} and finds that the current reference is not {{null}}. Right at that moment, another thread within findMessage() sets {{mList}} to {{null}}. Then the first thread retrieves {{mList}} again (now {{null}}) in order to call containsKey(), but because {{mList}} is {{null}}, a NullPointerException is thrown.
> This hypothetical scenario will probably not happen in real life because the first thread will probably retrieve the value of the {{mList}} field only once (see [https://stackoverflow.com/q/32996785/196844]). Nevertheless, I believe that the Java Language Specification does not _require_ an implementation to retrieve the value of the field only once.



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