system_server BINDER_TYPE_FD sockets using ashmem accessors

check if device is a character device, before calling
ashmem_get_size_region. We do not check if the st_rdev
matches /dev/ashmem. So this at least eliminates making
this call when associated with a socket.

Bug: 26374183
Change-Id: I68ed9d1c2cd4c47228ed065e3e18eb4151f038f4

libs/binder/Parcel.cpp

@@ -42,6 +42,9 @@
 #include <stdlib.h>
 #include <stdint.h>
 #include <sys/mman.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
 
 #ifndef INT32_MAX
 #define INT32_MAX ((int32_t)(2147483647))
@@ -123,8 +126,10 @@ void acquire_object(const sp<ProcessState>& proc,
             return;
         }
         case BINDER_TYPE_FD: {
-            if (obj.cookie != 0) {
-                if (outAshmemSize != NULL) {
+            if ((obj.cookie != 0) && (outAshmemSize != NULL)) {
+                struct stat st;
+                int ret = fstat(obj.handle, &st);
+                if (!ret && S_ISCHR(st.st_mode)) {
                     // 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) {
@@ -173,11 +178,15 @@ static void release_object(const sp<ProcessState>& proc,
             return;
         }
         case BINDER_TYPE_FD: {
-            if (outAshmemSize != NULL) {
-                if (obj.cookie != 0) {
-                    int size = ashmem_get_size_region(obj.handle);
-                    if (size > 0) {
-                        *outAshmemSize -= size;
+            if (obj.cookie != 0) { // owned
+                if (outAshmemSize != NULL) {
+                    struct stat st;
+                    int ret = fstat(obj.handle, &st);
+                    if (!ret && S_ISCHR(st.st_mode)) {
+                        int size = ashmem_get_size_region(obj.handle);
+                        if (size > 0) {
+                            *outAshmemSize -= size;
+                        }
                     }
 
                     close(obj.handle);