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https://issues.apache.org/jira/browse/LUCENE-7914?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16114209#comment-16114209
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ASF subversion and git services commented on LUCENE-7914:
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Commit 3610c8d1b8927fdb61667ea4c49f983bbe13a404 in lucene-solr's branch
refs/heads/branch_7x from [~jimczi]
[ https://git-wip-us.apache.org/repos/asf?p=lucene-solr.git;h=3610c8d ]
LUCENE-7914: Add a maximum recursion level in automaton recursive functions
(Operations.isFinite and Operations.topsortState) to prevent large automaton to
overflow the stack.
> 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
> Fix For: master (8.0), 7.1
>
> Attachments: LUCENE-7914.patch, LUCENE-7914.patch, LUCENE-7914.patch,
> LUCENE-7914.patch, 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
> infinite automatons only.
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