do not apply POSIX file attributes through symbolic links

log4j-core-test/src/test/java/org/apache/logging/log4j/core/appender/rolling/action/PosixViewAttributeActionTest.java

@@ -0,0 +1,104 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to you under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.logging.log4j.core.appender.rolling.action;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assumptions.assumeTrue;
+
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.attribute.PosixFilePermissions;
+import org.apache.logging.log4j.core.config.Configuration;
+import org.apache.logging.log4j.core.test.BasicConfigurationFactory;
+import org.apache.logging.log4j.core.util.FileUtils;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+
+/**
+ * Tests the {@code PosixViewAttributeAction} class.
+ */
+class PosixViewAttributeActionTest {
+
+    @BeforeAll
+    static void beforeClass() {
+        assumeTrue(FileUtils.isFilePosixAttributeViewSupported());
+    }
+
+    @Test
+    void testSymbolicLinksAreNotFollowed(@TempDir final Path tempDir) throws Exception {
+        // A file outside the scanned directory, that the action must not touch.
+        final Path outsider = tempDir.resolve("outsider.txt");
+        Files.write(outsider, "secret".getBytes(StandardCharsets.UTF_8));
+        Files.setPosixFilePermissions(outsider, PosixFilePermissions.fromString("rw-------"));
+
+        final Path baseDir = Files.createDirectory(tempDir.resolve("logs"));
+        final Path regularFile = baseDir.resolve("app-1.log");
+        Files.write(regularFile, "log".getBytes(StandardCharsets.UTF_8));
+        Files.setPosixFilePermissions(regularFile, PosixFilePermissions.fromString("rw-------"));
+        Files.createSymbolicLink(baseDir.resolve("app-2.log"), outsider);
+
+        final Configuration config = new BasicConfigurationFactory().new BasicConfiguration();
+        final PosixViewAttributeAction action = PosixViewAttributeAction.newBuilder()
+                .setBasePath(baseDir.toString())
+                .setFollowLinks(false)
+                .setMaxDepth(1)
+                .setPathConditions(PathCondition.EMPTY_ARRAY)
+                .setConfiguration(config)
+                .setFilePermissionsString("rw-rw-rw-")
+                .build();
+
+        action.execute();
+
+        assertEquals(
+                "rw-rw-rw-",
+                PosixFilePermissions.toString(Files.getPosixFilePermissions(regularFile)),
+                "regular file should have been updated");
+        assertEquals(
+                "rw-------",
+                PosixFilePermissions.toString(Files.getPosixFilePermissions(outsider)),
+                "symbolic link target should have been left alone");
+    }
+
+    @Test
+    void testSymbolicLinksAreFollowedWhenConfigured(@TempDir final Path tempDir) throws Exception {
+        final Path outsider = tempDir.resolve("outsider.txt");
+        Files.write(outsider, "secret".getBytes(StandardCharsets.UTF_8));
+        Files.setPosixFilePermissions(outsider, PosixFilePermissions.fromString("rw-------"));
+
+        final Path baseDir = Files.createDirectory(tempDir.resolve("logs"));
+        Files.createSymbolicLink(baseDir.resolve("app-2.log"), outsider);
+
+        final Configuration config = new BasicConfigurationFactory().new BasicConfiguration();
+        final PosixViewAttributeAction action = PosixViewAttributeAction.newBuilder()
+                .setBasePath(baseDir.toString())
+                .setFollowLinks(true)
+                .setMaxDepth(1)
+                .setPathConditions(PathCondition.EMPTY_ARRAY)
+                .setConfiguration(config)
+                .setFilePermissionsString("rw-rw-rw-")
+                .build();
+
+        action.execute();
+
+        assertEquals(
+                "rw-rw-rw-",
+                PosixFilePermissions.toString(Files.getPosixFilePermissions(outsider)),
+                "followLinks=\"true\" should still follow the link");
+    }
+}

log4j-core/src/main/java/org/apache/logging/log4j/core/appender/rolling/action/PosixViewAttributeAction.java

@@ -369,6 +369,10 @@ protected FileVisitor<Path> createFileVisitor(final Path basePath, final List<Pa
         return new SimpleFileVisitor<Path>() {
             @Override
             public FileVisitResult visitFile(final Path file, final BasicFileAttributes attrs) throws IOException {
+                if (!isFollowSymbolicLinks() && attrs.isSymbolicLink()) {
+                    LOGGER.trace("Not defining POSIX attribute on symbolic link {}", file);
+                    return FileVisitResult.CONTINUE;
+                }
                 for (final PathCondition pathFilter : conditions) {
                     final Path relative = basePath.relativize(file);
                     if (!pathFilter.accept(basePath, relative, attrs)) {

src/changelog/.2.x.x/fix_posix_view_attribute_symlink.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<entry xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xmlns="https://logging.apache.org/xml/ns"
+       xsi:schemaLocation="https://logging.apache.org/xml/ns https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
+       type="fixed">
+  <issue id="4229" link="https://github.com/apache/logging-log4j2/pull/4229"/>
+  <description format="asciidoc">Stop `PosixViewAttribute` from applying permissions and ownership through symbolic links found in `basePath` unless `followLinks` is set to `true`.</description>
+</entry>