Add a GUID to base::SharedMemoryHandle.

base/memory/shared_memory_win.cc

Index: base/memory/shared_memory_win.cc
diff --git a/base/memory/shared_memory_win.cc b/base/memory/shared_memory_win.cc
index daa700da6a373cd491ce56228f9b58037517c23f..598a50dc7a68f93815f4185b0cbd335f55c5b72a 100644
--- a/base/memory/shared_memory_win.cc
+++ b/base/memory/shared_memory_win.cc
@@ -13,6 +13,7 @@
 #include "base/rand_util.h"
 #include "base/strings/stringprintf.h"
 #include "base/strings/utf_string_conversions.h"
+#include "base/unguessable_token.h"
 
 namespace {
 
@@ -240,8 +241,9 @@ bool SharedMemory::Create(const SharedMemoryCreateOptions& options) {
                          rand_values[2], rand_values[3]);
   }
   DCHECK(!name_.empty());
-  shm_ = SharedMemoryHandle(CreateFileMappingWithReducedPermissions(
-      &sa, rounded_size, name_.c_str()));
+  shm_ = SharedMemoryHandle(
+      CreateFileMappingWithReducedPermissions(&sa, rounded_size, name_.c_str()),
+      UnguessableToken::Create());
   if (!shm_.IsValid()) {
     // The error is logged within CreateFileMappingWithReducedPermissions().
     return false;
@@ -279,8 +281,13 @@ bool SharedMemory::Open(const std::string& name, bool read_only) {
     access |= FILE_MAP_WRITE;
   name_ = ASCIIToUTF16(name);
   read_only_ = read_only;
+
+  // This form of sharing shared memory is deprecated. https://crbug.com/345734.
+  // Technically, we should also pass the GUID from the original shared memory
+  // region. Instead, we should just remove all instances of this.

[Nico, 2017/05/05 18:34:36]

Likewise?

What's the failure case if someone calls this function? Just shm memory being
double-counted? Is there anything that prevents new callers of this? Are you
going to work on removing calls to this function – sounds like this isn't really
possible?

[erikchen, 2017/05/05 19:29:33]

Done.

   shm_ = SharedMemoryHandle(
-      OpenFileMapping(access, false, name_.empty() ? nullptr : name_.c_str()));
+      OpenFileMapping(access, false, name_.empty() ? nullptr : name_.c_str()),
+      UnguessableToken::Create());
   if (!shm_.IsValid())
     return false;
   // If a name specified assume it's an external section.
@@ -332,7 +339,7 @@ SharedMemoryHandle SharedMemory::GetReadOnlyHandle() {
                          FILE_MAP_READ | SECTION_QUERY, FALSE, 0)) {
     return SharedMemoryHandle();
   }
-  SharedMemoryHandle handle = SharedMemoryHandle(result);
+  SharedMemoryHandle handle = SharedMemoryHandle(result, shm_.GetGUID());
   handle.SetOwnershipPassesToIPC(true);
   return handle;
 }