From e4f60cce8552a565efacf4907242574b9e00492d Mon Sep 17 00:00:00 2001
From: John Reck <jreck@google.com>
Date: Mon, 7 Aug 2017 11:17:06 -0700
Subject: SharedMemory API changes

Hides getFd & getFileDescriptor due to lifecycle concenrs.
Adds ASharedMemory_dupFromJava to allow sharing a shared
memory region between Java & Native as safe as possible.
Mis-use results in an FD leak instead of double-close.

Bug: 64394076
Test: SharedMemory CTS tests
Change-Id: I01a5eb978fc4e99559a79baac75754c32f13bdc4
---
 native/android/sharedmem.cpp | 43 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)

(limited to 'native/android/sharedmem.cpp')

diff --git a/native/android/sharedmem.cpp b/native/android/sharedmem.cpp
index 9d029dfad41a..757aaecab40d 100644
--- a/native/android/sharedmem.cpp
+++ b/native/android/sharedmem.cpp
@@ -14,10 +14,36 @@
  * limitations under the License.
  */
 
+#include <jni.h>
+
 #include <android/sharedmem.h>
+#include <android/sharedmem_jni.h>
 #include <cutils/ashmem.h>
+#include <log/log.h>
 #include <utils/Errors.h>
 
+#include <mutex>
+#include <unistd.h>
+
+static struct {
+    jclass clazz;
+    jmethodID getFd;
+} sSharedMemory;
+
+static void jniInit(JNIEnv* env) {
+    static std::once_flag sJniInitialized;
+    std::call_once(sJniInitialized, [](JNIEnv* env) {
+        jclass clazz = env->FindClass("android/os/SharedMemory");
+        LOG_ALWAYS_FATAL_IF(clazz == nullptr, "Failed to find android.os.SharedMemory");
+        sSharedMemory.clazz = (jclass) env->NewGlobalRef(clazz);
+        LOG_ALWAYS_FATAL_IF(sSharedMemory.clazz == nullptr,
+                "Failed to create global ref of android.os.SharedMemory");
+        sSharedMemory.getFd = env->GetMethodID(sSharedMemory.clazz, "getFd", "()I");
+        LOG_ALWAYS_FATAL_IF(sSharedMemory.getFd == nullptr,
+                "Failed to find method SharedMemory#getFd()");
+    }, env);
+}
+
 int ASharedMemory_create(const char *name, size_t size) {
     if (size == 0) {
         return android::BAD_VALUE;
@@ -32,3 +58,20 @@ size_t ASharedMemory_getSize(int fd) {
 int ASharedMemory_setProt(int fd, int prot) {
     return ashmem_set_prot_region(fd, prot);
 }
+
+int ASharedMemory_dupFromJava(JNIEnv* env, jobject javaSharedMemory) {
+    if (env == nullptr || javaSharedMemory == nullptr) {
+        return -1;
+    }
+    jniInit(env);
+    if (!env->IsInstanceOf(javaSharedMemory, sSharedMemory.clazz)) {
+        ALOGW("ASharedMemory_dupFromJava called with object "
+                "that's not an instanceof android.os.SharedMemory");
+        return -1;
+    }
+    int fd = env->CallIntMethod(javaSharedMemory, sSharedMemory.getFd);
+    if (fd != -1) {
+        fd = dup(fd);
+    }
+    return fd;
+}
-- 
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