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Soundness: try/catch is checked as if the catch block always runs

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  • ¿Algo no está bien?
#364 0 comentarios 0 reacciones 0 asignados Ver en GitHub

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Evaluación

Dificultad
4/5
Tiempo estimado
3-5 días
Aptitud para principiantes
50/100
Tipo de issue
Error
Claridad
Bien especificado
Estado de actividad
Activo
Stack tecnológico
java
Área
compilers

Línea de trabajo

Locate where the verifier visits try/catch statements (search the visitor/checker for the try-statement case) and compare it with how if/else merges branch states at the join point — the issue says try/catch is currently sequenced instead of merged. Work out how both branches (normal exit from try, entry into catch at an arbitrary point) should be joined, and how the state after the join relates to the state on entry. Done means both reproducers in the issue report errors, the swapped-value case reports correctly, and existing verification tests still pass; add the reproducers as regression tests.

Escrito por el modelo de indexación a partir del texto del issue.

Descripción

bug

Impact: a real bug passes verification (false negative).

Description

The verifier checks try and catch blocks one after the other, so after a try/catch a variable keeps whatever the catch block last assigned. The path where the try finishes normally is lost. An if/else instead merges both branches after the join, and try/catch should be merged the same way.

Also, an exception can be thrown at any point in the try. The catch block should therefore not assume the try ran to completion, or that it never ran at all.

Minimal reproducer

import liquidjava.specification.ExternalRefinementsFor;
import liquidjava.specification.StateRefinement;
import liquidjava.specification.StateSet;

@ExternalRefinementsFor("java.lang.Throwable")
@StateSet({"withThrowable", "noThrowable"})
interface ThrowableRefinements {
    @StateRefinement(to = "noThrowable(this)")
    void Throwable(String message);

    @StateRefinement(to = "withThrowable(this)")
    void Throwable(String message, Throwable cause);

    @StateRefinement(from = "noThrowable(this)", to = "withThrowable(this)")
    Throwable initCause(Throwable cause);
}

public class Repro {
    static void load() throws Exception { throw new Exception("x"); }

    static void m() {
        Throwable t = new Throwable("start");
        try {
            load();
            t = new Throwable("try", new RuntimeException()); // withThrowable
        } catch (Exception e) {
            t = new Throwable("catch");                       // noThrowable
        }
        t.initCause(new RuntimeException()); // not reported, but t is withThrowable if load() returns
    }
}

Expected: a State Refinement Error on t.initCause(...), because t may be withThrowable.

Actual: Correct! Passed Verification.

Same bug with value refinements

static void m() {
    int y = 0;
    try {
        load();
        y = -5;
    } catch (Exception e) {
        y = 7;
    }
    @Refinement("_ > 0")
    int z = y; // not reported, but y == -5 if load() returns
}

Actual: Correct! Passed Verification. If the values are swapped (5 in the try, -5 in the catch), the error is reported, but as z == -5 is not a subtype of z > 0: only the catch path is considered.

Found while reviewing #362 (catch parameters, #333).

Lenguaje dominante
Java
Estrellas
67
Forks
36
Merge medio
2 d 3 h
PR fusionados (30 d)
29

Preparar el entorno

Primeros pasos

  1. Lee el issue completo y luego la guía de contribución del proyecto.
  2. Comenta en el issue que vas a ocuparte — evita que dos personas hagan lo mismo.
  3. Haz un fork del repositorio y trabaja en una rama.
  4. Abre un pull request que haga referencia al número del issue.

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