Source added

app/jni/Android.mk

@@ -0,0 +1,11 @@
+JNI_DIR := $(call my-dir)
+
+include $(CLEAR_VARS)
+
+LOCAL_MODULE     := native-utils
+LOCAL_C_INCLUDES := $(JNI_DIR)/utils/
+LOCAL_CFLAGS     += -Wall
+
+LOCAL_SRC_FILES := $(JNI_DIR)/utils/org_thoughtcrime_securesms_util_FileUtils.cpp
+
+include $(BUILD_SHARED_LIBRARY)

app/jni/Application.mk

@@ -0,0 +1,6 @@
+# Built with NDK 19.2.5345600
+APP_ABI      := armeabi-v7a x86 arm64-v8a x86_64
+APP_PLATFORM := android-19
+APP_STL      := c++_static
+APP_CPPFLAGS += -fexceptions
+APP_OPTIM    := debug

app/jni/utils/org_thoughtcrime_securesms_util_FileUtils.cpp

@@ -0,0 +1,45 @@
+#include "org_thoughtcrime_securesms_util_FileUtils.h"
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+#include <linux/memfd.h>
+#include <syscall.h>
+
+jint JNICALL Java_org_thoughtcrime_securesms_util_FileUtils_getFileDescriptorOwner
+  (JNIEnv *env, jclass clazz, jobject fileDescriptor)
+{
+  jclass fdClass = env->GetObjectClass(fileDescriptor);
+
+  if (fdClass == NULL) {
+    return -1;
+  }
+
+  jfieldID fdFieldId = env->GetFieldID(fdClass, "descriptor", "I");
+
+  if (fdFieldId == NULL) {
+    return -1;
+  }
+
+  int fd = env->GetIntField(fileDescriptor, fdFieldId);
+
+  struct stat stat_struct;
+
+  if (fstat(fd, &stat_struct) != 0) {
+    return -1;
+  }
+
+  return stat_struct.st_uid;
+}
+
+JNIEXPORT jint JNICALL Java_org_thoughtcrime_securesms_util_FileUtils_createMemoryFileDescriptor
+  (JNIEnv *env, jclass clazz, jstring jname)
+{
+  const char *name = env->GetStringUTFChars(jname, NULL);
+
+  int fd = syscall(SYS_memfd_create, name, MFD_CLOEXEC);
+
+  env->ReleaseStringUTFChars(jname, name);
+
+  return fd;
+}

app/jni/utils/org_thoughtcrime_securesms_util_FileUtils.h

@@ -0,0 +1,29 @@
+/* DO NOT EDIT THIS FILE - it is machine generated */
+#include <jni.h>
+/* Header for class org_thoughtcrime_securesms_util_FileUtils */
+
+#ifndef _Included_org_thoughtcrime_securesms_util_FileUtils
+#define _Included_org_thoughtcrime_securesms_util_FileUtils
+#ifdef __cplusplus
+extern "C" {
+#endif
+/*
+ * Class:     org_thoughtcrime_securesms_util_FileUtils
+ * Method:    getFileDescriptorOwner
+ * Signature: (Ljava/io/FileDescriptor;)I
+ */
+JNIEXPORT jint JNICALL Java_org_thoughtcrime_securesms_util_FileUtils_getFileDescriptorOwner
+  (JNIEnv *, jclass, jobject);
+
+/*
+ * Class:     org_thoughtcrime_securesms_util_FileUtils
+ * Method:    createMemoryFileDescriptor
+ * Signature: (Ljava/lang/String;)I
+ */
+JNIEXPORT jint JNICALL Java_org_thoughtcrime_securesms_util_FileUtils_createMemoryFileDescriptor
+  (JNIEnv *, jclass, jstring);
+
+#ifdef __cplusplus
+}
+#endif
+#endif