[LUCENE-8672] NullPointerException in o.a.solr.search.facet.FacetFieldProcessor.findTopSlots()

• Type: Bug
• Status: Closed
• Priority: Minor
• Resolution: Invalid
• Affects Version/s: 9.0

Environment

Steps to reproduce

• Use a Linux machine.
• Build commit ea2c8ba of Solr as described in the section below.
• Build the films collection as described below.
• Start the server using the command ./bin/solr start -f -p 8983 -s /tmp/home
• Request the URL given in the bug description.

Compiling the server

git clone https://github.com/apache/lucene-solr
cd lucene-solr
git checkout ea2c8ba
ant compile
cd solr
ant server

Building the collection

We followed Exercise 2 from the Solr Tutorial. The attached file (home.zip) gives the contents of folder /tmp/home that you will obtain by following the steps below:

mkdir -p /tmp/home
echo '<?xml version="1.0" encoding="UTF-8" ?><solr></solr>' > /tmp/home/solr.xml

In one terminal start a Solr instance in foreground:

./bin/solr start -f -p 8983 -s /tmp/home

In another terminal, create a collection of movies, with no shards and no replication, and initialize it:

bin/solr create -c films
curl -X POST -H 'Content-type:application/json' --data-binary '{"add-field": {"name":"name", "type":"text_general", "multiValued":false, "stored":true}}' http://localhost:8983/solr/films/schema
curl -X POST -H 'Content-type:application/json' --data-binary '{"add-copy-field" : {"source":"*","dest":"_text_"}}' http://localhost:8983/solr/films/schema
./bin/post -c films example/films/films.json

• Lucene Fields: New
• Assignee: Unassigned
• Reporter: Cesar Rodriguez
• Created: 31/Jan/19 11:19
• Updated: 28/Aug/22 15:41
• Resolved: 31/Jan/19 11:25

Description

Requesting the following URL causes Solr to return an HTTP 500 error response:

http://localhost:8983/solr/films/select?facet.sort=asc&facet=on&bf=2&q=x&facet.version=2&facet.field=genre

The error response seems to be caused by the following uncaught exception:

java.lang.NullPointerException
	at org.apache.solr.search.facet.FacetFieldProcessor.lambda$findTopSlots$1(FacetFieldProcessor.java:325)
	at org.apache.solr.search.facet.FacetFieldProcessor$1.lessThan(FacetFieldProcessor.java:331)
	at org.apache.solr.search.facet.FacetFieldProcessor$1.lessThan(FacetFieldProcessor.java:329)
	at org.apache.lucene.util.PriorityQueue.upHeap(PriorityQueue.java:254)
	at org.apache.lucene.util.PriorityQueue.add(PriorityQueue.java:131)
	at org.apache.solr.search.facet.FacetFieldProcessor.findTopSlots(FacetFieldProcessor.java:363)
	at org.apache.solr.search.facet.FacetFieldProcessorByArray.calcFacets(FacetFieldProcessorByArray.java:114)
	at org.apache.solr.search.facet.FacetFieldProcessorByArray.process(FacetFieldProcessorByArray.java:62)
	at org.apache.solr.search.facet.FacetRequest.process(FacetRequest.java:401)
	at org.apache.solr.search.facet.FacetProcessor.processSubs(FacetProcessor.java:472)
	at org.apache.solr.search.facet.FacetProcessor.fillBucket(FacetProcessor.java:429)
	at org.apache.solr.search.facet.FacetQueryProcessor.process(FacetQuery.java:64)
	at org.apache.solr.search.facet.FacetRequest.process(FacetRequest.java:401)
	at org.apache.solr.search.facet.FacetModule.process(FacetModule.java:139)
	at org.apache.solr.handler.component.SearchHandler.handleRequestBody(SearchHandler.java:298)
	at org.apache.solr.handler.RequestHandlerBase.handleRequest(RequestHandlerBase.java:199)
	at org.apache.solr.core.SolrCore.execute(SolrCore.java:2559)
	at org.apache.solr.servlet.HttpSolrCall.execute(HttpSolrCall.java:711)
	at org.apache.solr.servlet.HttpSolrCall.call(HttpSolrCall.java:516)
	at org.apache.solr.servlet.SolrDispatchFilter.doFilter(SolrDispatchFilter.java:394)
	at org.apache.solr.servlet.SolrDispatchFilter.doFilter(SolrDispatchFilter.java:340)
	at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1602)
[...]

Removing any parameter in the URL makes the NPE disappear, so all URL parameters seem to be involved.

Method org.apache.solr.search.facet.FacetFieldProcessor.findTopSlots(), at line 316 retrieves the field sortAcc, which is null. This null pointer is subsequently used in a lambda expression, line 325 (and 320!). I guess the problem is that some input validation is missing?

We found this bug using Diffblue Microservices Testing. Find more information on this fuzz testing campaign.