java/unsafe-double-checked-locking: not reported when the outer guard is written as !(!(x == null))

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Avaliação

Dificuldade
4/5
Tempo estimado
3-5 dias
Facilidade para iniciantes
42/100
Tipo de issue
Bug
Clareza
Claramente especificada
Status de atividade
Ativa
Stack de tecnologia
java
Domínio
devtools, security

Direção de pesquisa

Start from the java/unsafe-double-checked-locking query in the java-queries pack and the guard logic it uses to recognise the outer helper == null check. Reproduce with the two sample files, Dcl.java and DclV.java, in a test directory for that query. The gap is that !(!(helper == null)) is not treated as equivalent to helper == null. Done means DclV is reported like Dcl, with a test case added for the double-negated form.

Escrita pelo modelo de indexação a partir do texto da issue.

Descrição

Java

Description of the issue

The query reports double-checked locking on a non-volatile field in Dcl.getHelper(). In DclV.getHelper() the outer guard is !(!(helper == null)) instead of helper == null, with the inner check and the field unchanged. Nothing is reported for DclV, though it's the same test.

Query: java/unsafe-double-checked-locking (codeql/java-queries 1.1.10)

CodeQL CLI: 2.27.2

Code samples

seed/Dcl.java:

class Dcl {
    private Helper helper;
    Helper getHelper() {
        if (helper == null) {                 // query fires here
            synchronized (this) {
                if (helper == null) {
                    helper = new Helper();
                }
            }
        }
        return helper;
    }
    static class Helper {
        int x;
    }
}

variant/DclV.java:

class DclV {
    private Helper helper;
    Helper getHelper() {
        if (!(!(helper == null))) {           // equivalent outer guard; query silent
            synchronized (this) {
                if (helper == null) {
                    helper = new Helper();
                }
            }
        }
        return helper;
    }
    static class Helper {
        int x;
    }
}

How to reproduce

codeql database create db --language=java --build-mode=none \
    --source-root=<one directory> --overwrite
codeql database analyze db \
    codeql/java-queries:codeql-suites/java-security-and-quality.qls \
    --format=csv --output=out.csv
# one database per directory

Expected result

"Double-checked locking on the non-volatile field helper is not thread-safe" on DclV, as on Dcl.

Output of the commands above:

### CodeQL 2.27.2  query: java/unsafe-double-checked-locking
### suite: java-security-and-quality.qls, --build-mode=none, per-file isolated databases
### extraction JDK: openjdk version "21.0.11" 2026-04-21 LTS

--- SEED -- expected: query fires (seed/)
"Double-checked locking is not thread-safe","A repeated check on a non-volatile field is not thread-safe, and

--- VARIANT -- expected: query fires, actual: not reported (the bug) (variant/)
    (query reported nothing)
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