[jira] [Commented] (LUCENE-7914) Add safeguards to RegExp.toAutomaton and Operations

["Robert Muir (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/LUCENE-7914?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16108729#comment-16108729 ] 

Robert Muir commented on LUCENE-7914:
-------------------------------------

Sorry, but prefixquery is definitely infinite. Besides this logic being wrong, I really don't like the "trillean" and additional ctor added to the public API.


> Add safeguards to RegExp.toAutomaton and Operations
> ---------------------------------------------------
>
>                 Key: LUCENE-7914
>                 URL: https://issues.apache.org/jira/browse/LUCENE-7914
>             Project: Lucene - Core
>          Issue Type: Bug
>            Reporter: Jim Ferenczi
>         Attachments: LUCENE-7914.patch
>
>
> When creating an automaton from a regexp, some operators can create more states than maxDeterminizedStates:
> {code}
> a{10000}
> {code}
> The example above <b>creates</b> a single path with 10k states already determinized so maxDeterminizedStates is not checked. 
> Some operations on automaton like Operations.isFinite or Operations.topoSortStates are recursive and the maximum level of recursion depends on the longest path in the automaton. So a large automaton like above can exceed java's stack.
> In most of the cases we are covered by maxDeterminizedStates but there will always be adversarial cases where a large automaton is created from a small input so I think we should also have safeguards in the recursive methods. 
> I've attached a patch that adds a max recursion level to Operations.isFinite and Operations.topoSortStates in order to limit stack overflows. The limit is set to 1000 so any automaton with a path bigger than 1000 would throw an IllegalStateException.
> The patch also uses maxDeterminizedStates to limit the number of states that a repeat operator can create and throw a TooComplex..Exception when this limit is reached.
> Finally the patch adds the ability to skip Operations.isFinite on AutomatonQuery and uses this as an optimization for PrefixQuery that uses finite automatons only.



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