system_server BINDER_TYPE_FD driver ashmem accessors

check if device matches the ashmem rdev, before calling
ashmem_get_size_region. This eliminates making this call
when associated with other driver file descriptors.

Bug: 26374183
Bug: 26918423
Bug: 26871259
Change-Id: I1f88c2c93ea35a73c8e14125f3d1a6c67fa4f15b

1 files changed, 30 insertions, 2 deletions

diff --git a/libs/binder/Parcel.cpp b/libs/binder/Parcel.cpp
index 2e9e658fd9..4a6bce8f11 100644
--- a/libs/binder/Parcel.cpp
+++ b/libs/binder/Parcel.cpp
@@ -18,7 +18,9 @@
 //#define LOG_NDEBUG 0
 
 #include <errno.h>
+#include <fcntl.h>
 #include <inttypes.h>
+#include <pthread.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -95,6 +97,32 @@ enum {
     BLOB_ASHMEM_MUTABLE = 2,
 };
 
+static dev_t ashmem_rdev()
+{
+    static dev_t __ashmem_rdev;
+    static pthread_mutex_t __ashmem_rdev_lock = PTHREAD_MUTEX_INITIALIZER;
+
+    pthread_mutex_lock(&__ashmem_rdev_lock);
+
+    dev_t rdev = __ashmem_rdev;
+    if (!rdev) {
+        int fd = TEMP_FAILURE_RETRY(open("/dev/ashmem", O_RDONLY));
+        if (fd >= 0) {
+            struct stat st;
+
+            int ret = TEMP_FAILURE_RETRY(fstat(fd, &st));
+            close(fd);
+            if ((ret >= 0) && S_ISCHR(st.st_mode)) {
+                rdev = __ashmem_rdev = st.st_rdev;
+            }
+        }
+    }
+
+    pthread_mutex_unlock(&__ashmem_rdev_lock);
+
+    return rdev;
+}
+
 void acquire_object(const sp<ProcessState>& proc,
     const flat_binder_object& obj, const void* who, size_t* outAshmemSize)
 {
@@ -126,7 +154,7 @@ void acquire_object(const sp<ProcessState>& proc,
             if ((obj.cookie != 0) && (outAshmemSize != NULL)) {
                 struct stat st;
                 int ret = fstat(obj.handle, &st);
-                if (!ret && S_ISCHR(st.st_mode)) {
+                if (!ret && S_ISCHR(st.st_mode) && (st.st_rdev == ashmem_rdev())) {
                     // If we own an ashmem fd, keep track of how much memory it refers to.
                     int size = ashmem_get_size_region(obj.handle);
                     if (size > 0) {
@@ -179,7 +207,7 @@ static void release_object(const sp<ProcessState>& proc,
                 if (outAshmemSize != NULL) {
                     struct stat st;
                     int ret = fstat(obj.handle, &st);
-                    if (!ret && S_ISCHR(st.st_mode)) {
+                    if (!ret && S_ISCHR(st.st_mode) && (st.st_rdev == ashmem_rdev())) {
                         int size = ashmem_get_size_region(obj.handle);
                         if (size > 0) {
                             *outAshmemSize -= size;