fix(skills): prevent path traversal in LocalSkillSource

core/src/main/java/com/google/adk/skills/LocalSkillSource.java

@@ -41,6 +41,12 @@ public LocalSkillSource(Path skillsBasePath) {
 
   @Override
   public Single<ImmutableList<String>> listResources(String skillName, String resourceDirectory) {
+    try {
+      validatePathWithinBase(skillsBasePath, skillName);
+      validatePathWithinBase(skillsBasePath.resolve(skillName), resourceDirectory);
+    } catch (SkillSourceException e) {
+      return Single.error(e);
+    }
     Path skillDir = skillsBasePath.resolve(skillName);
     if (!isDirectory(skillDir)) {
       return Single.error(new SkillSourceException("Skill not found: " + skillName));
@@ -86,6 +92,12 @@ protected Flowable<SkillMdPath> listSkills() {
 
   @Override
   protected Single<Path> findResourcePath(String skillName, String resourcePath) {
+    try {
+      validatePathWithinBase(skillsBasePath, skillName);
+      validatePathWithinBase(skillsBasePath.resolve(skillName), resourcePath);
+    } catch (SkillSourceException e) {
+      return Single.error(e);
+    }
     Path file = skillsBasePath.resolve(skillName).resolve(resourcePath);
     if (!Files.exists(file)) {
       return Single.error(new SkillSourceException("Resource not found: " + file));
@@ -95,6 +107,11 @@ protected Single<Path> findResourcePath(String skillName, String resourcePath) {
 
   @Override
   protected Single<Path> findSkillMdPath(String skillName) {
+    try {
+      validatePathWithinBase(skillsBasePath, skillName);
+    } catch (SkillSourceException e) {
+      return Single.error(e);
+    }
     Path skillDir = skillsBasePath.resolve(skillName);
     if (!isDirectory(skillDir)) {
       return Single.error(new SkillSourceException("Skill directory not found: " + skillName));
@@ -115,4 +132,23 @@ private Optional<Path> findSkillMd(Path dir) {
         .or(() -> Optional.of(dir.resolve("skill.md")))
         .filter(Files::exists);
   }
+
+  /**
+   * Validates that {@code component} does not escape {@code base} when resolved against it.
+   *
+   * @throws SkillSourceException if the resolved path would be outside {@code base}
+   */
+  private static void validatePathWithinBase(Path base, String component)
+      throws SkillSourceException {
+    if (Path.of(component).isAbsolute()) {
+      throw new SkillSourceException("Absolute paths are not allowed: " + component);
+    }
+    Path normalizedBase = base.normalize().toAbsolutePath();
+    Path resolved = base.resolve(component).normalize().toAbsolutePath();
+    if (!resolved.startsWith(normalizedBase)) {
+      throw new SkillSourceException(
+          "Path traversal detected; component must remain within its parent directory: "
+              + component);
+    }
+  }
 }

core/src/test/java/com/google/adk/skills/LocalSkillSourceTest.java

@@ -250,4 +250,70 @@ public void testListSkillMdPaths_skillSourceException() throws IOException {
     RuntimeException exception = assertThrows(RuntimeException.class, single::blockingGet);
     assertThat(exception).hasCauseThat().isInstanceOf(SkillSourceException.class);
   }
+
+  @Test
+  public void testLoadResource_pathTraversalInSkillName() throws IOException {
+    Path skillsBase = tempFolder.getRoot().toPath().resolve("skills");
+    Files.createDirectory(skillsBase);
+
+    SkillSource source = new LocalSkillSource(skillsBase);
+    var single = source.loadResource("../other-dir", "file.txt");
+    RuntimeException exception = assertThrows(RuntimeException.class, single::blockingGet);
+    assertThat(exception).hasCauseThat().isInstanceOf(SkillSourceException.class);
+    assertThat(exception).hasCauseThat().hasMessageThat().contains("Path traversal detected");
+  }
+
+  @Test
+  public void testLoadResource_pathTraversalInResourcePath() throws IOException {
+    Path skillsBase = tempFolder.getRoot().toPath().resolve("skills");
+    Files.createDirectory(skillsBase);
+    Path skillDir = skillsBase.resolve("my-skill");
+    Files.createDirectory(skillDir);
+
+    SkillSource source = new LocalSkillSource(skillsBase);
+    var single = source.loadResource("my-skill", "../../../etc/passwd");
+    RuntimeException exception = assertThrows(RuntimeException.class, single::blockingGet);
+    assertThat(exception).hasCauseThat().isInstanceOf(SkillSourceException.class);
+    assertThat(exception).hasCauseThat().hasMessageThat().contains("Path traversal detected");
+  }
+
+  @Test
+  public void testLoadResource_absoluteResourcePath() throws IOException {
+    Path skillsBase = tempFolder.getRoot().toPath().resolve("skills");
+    Files.createDirectory(skillsBase);
+    Path skillDir = skillsBase.resolve("my-skill");
+    Files.createDirectory(skillDir);
+
+    SkillSource source = new LocalSkillSource(skillsBase);
+    var single = source.loadResource("my-skill", "/etc/passwd");
+    RuntimeException exception = assertThrows(RuntimeException.class, single::blockingGet);
+    assertThat(exception).hasCauseThat().isInstanceOf(SkillSourceException.class);
+    assertThat(exception).hasCauseThat().hasMessageThat().contains("Absolute paths are not allowed");
+  }
+
+  @Test
+  public void testListResources_pathTraversalInSkillName() throws IOException {
+    Path skillsBase = tempFolder.getRoot().toPath().resolve("skills");
+    Files.createDirectory(skillsBase);
+
+    SkillSource source = new LocalSkillSource(skillsBase);
+    var single = source.listResources("../../etc", "passwd");
+    RuntimeException exception = assertThrows(RuntimeException.class, single::blockingGet);
+    assertThat(exception).hasCauseThat().isInstanceOf(SkillSourceException.class);
+    assertThat(exception).hasCauseThat().hasMessageThat().contains("Path traversal detected");
+  }
+
+  @Test
+  public void testListResources_pathTraversalInResourceDirectory() throws IOException {
+    Path skillsBase = tempFolder.getRoot().toPath().resolve("skills");
+    Files.createDirectory(skillsBase);
+    Path skillDir = skillsBase.resolve("my-skill");
+    Files.createDirectory(skillDir);
+
+    SkillSource source = new LocalSkillSource(skillsBase);
+    var single = source.listResources("my-skill", "../other-skill");
+    RuntimeException exception = assertThrows(RuntimeException.class, single::blockingGet);
+    assertThat(exception).hasCauseThat().isInstanceOf(SkillSourceException.class);
+    assertThat(exception).hasCauseThat().hasMessageThat().contains("Path traversal detected");
+  }
 }