syslog.h: implement LOG_PERROR.

This is the one openlog() flag that toybox uses. We should probably try
to unify toybox's POSIX logger and Android-specific log at some point,
and this will help.

Also fix our behavior with an empty format string, noticed while adding
tests.

Test: treehugger
Test: adb shell logger -s foo
Change-Id: Ic027e78a460be3db83cc4c6f9946c9efa22be6e1

libc/bionic/syslog.cpp

@@ -18,18 +18,22 @@
 #include <stdlib.h>
 #include <string.h>
 #include <syslog.h>
+#include <unistd.h>
 
 #include <async_safe/log.h>
 
 static const char* syslog_log_tag = nullptr;
 static int syslog_priority_mask = 0xff;
+static int syslog_options = 0;
 
 void closelog() {
   syslog_log_tag = nullptr;
+  syslog_options = 0;
 }
 
-void openlog(const char* log_tag, int /*options*/, int /*facility*/) {
+void openlog(const char* log_tag, int options, int /*facility*/) {
   syslog_log_tag = log_tag;
+  syslog_options = options;
 }
 
 int setlogmask(int new_mask) {
@@ -73,10 +77,16 @@ void vsyslog(int priority, const char* fmt, va_list args) {
     android_log_priority = ANDROID_LOG_DEBUG;
   }
 
-  // We can't let async_safe_format_log do the formatting because it doesn't support
-  // all the printf functionality.
+  // We can't let async_safe_format_log do the formatting because it doesn't
+  // support all the printf functionality.
   char log_line[1024];
-  vsnprintf(log_line, sizeof(log_line), fmt, args);
+  int n = vsnprintf(log_line, sizeof(log_line), fmt, args);
+  if (n < 0) return;
 
   async_safe_format_log(android_log_priority, log_tag, "%s", log_line);
+  if ((syslog_options & LOG_PERROR) != 0) {
+    bool have_newline =
+        (n > 0 && n < static_cast<int>(sizeof(log_line)) && log_line[n - 1] == '\n');
+    dprintf(STDERR_FILENO, "%s: %s%s", log_tag, log_line, have_newline ? "" : "\n");
+  }
 }

libc/include/syslog.h

@@ -112,17 +112,21 @@ __BEGIN_DECLS
  */
 #define LOG_UPTO(pri) ((1 << ((pri)+1)) - 1)
 
-/** openlog() options are currently ignored on Android. */
+/** openlog() option ignored on Android. */
 #define LOG_PID    0x01
-/** openlog() options are currently ignored on Android. */
+/** openlog() option ignored on Android. */
 #define LOG_CONS   0x02
-/** openlog() options are currently ignored on Android. */
+/** openlog() option ignored on Android. */
 #define LOG_ODELAY 0x04
-/** openlog() options are currently ignored on Android. */
+/** openlog() option ignored on Android. */
 #define LOG_NDELAY 0x08
-/** openlog() options are currently ignored on Android. */
+/** openlog() option ignored on Android. */
 #define LOG_NOWAIT 0x10
-/** openlog() options are currently ignored on Android. */
+/**
+ * openlog() option to log to stderr as well as the system log.
+ *
+ * Available since API level 34 (ignored before then).
+ */
 #define LOG_PERROR 0x20
 
 /**

tests/Android.bp

@@ -503,6 +503,7 @@ cc_test_library {
         "sys_vfs_test.cpp",
         "sys_wait_test.cpp",
         "sys_xattr_test.cpp",
+        "syslog_test.cpp",
         "system_properties_test.cpp",
         "system_properties_test2.cpp",
         "termios_test.cpp",

tests/syslog_test.cpp

@@ -0,0 +1,74 @@
+/*
+ * Copyright (C) 2023 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <syslog.h>
+
+#include <errno.h>
+#include <gtest/gtest.h>
+
+#include "utils.h"
+
+TEST(syslog, syslog_percent_m) {
+  ExecTestHelper eth;
+  eth.Run(
+      [&]() {
+        openlog("foo", LOG_PERROR, LOG_AUTH);
+        errno = EINVAL;
+        syslog(LOG_ERR, "a b c: %m");
+        closelog();
+        exit(0);
+      },
+      0, "foo: a b c: Invalid argument\n");
+}
+
+TEST(syslog, syslog_empty) {
+  ExecTestHelper eth;
+  eth.Run(
+      [&]() {
+        openlog("foo", LOG_PERROR, LOG_AUTH);
+        errno = EINVAL;
+        syslog(LOG_ERR, "");
+        closelog();
+        exit(0);
+      },
+      0, "foo: \n");
+}
+
+TEST(syslog, syslog_truncation) {
+  ExecTestHelper eth;
+  eth.Run(
+      [&]() {
+        openlog("bar", LOG_PERROR, LOG_AUTH);
+        char too_long[2048] = {};
+        memset(too_long, 'x', sizeof(too_long) - 1);
+        syslog(LOG_ERR, "%s", too_long);
+        closelog();
+        exit(0);
+      },
+      0, "bar: x{1023}\n");
+}