Memory Mapped files access control classes missing in dotnet core

[ChrisUnityArto]

Hi!

This Issue #941
And this PR #465
were both closed because no users had requested the ability to set access rules on memory mapped files.

I'm a user, and I'm requesting it now please.

So is this team : https://stackoverflow.com/questions/57085421/sharing-of-global-in-memory-memory-mapped-file

This is a requirement for me as my team have got some bug reports that our existing code which uses MemoryMapped files CreateNew() method is reporting a file not found error on some user's machines.

The fix suggested here which looks like it would work for us
https://stackoverflow.com/questions/20363839/opening-a-memory-mapped-file-causes-filenotfoundexception-when-deployed-in-iis

requires dotnet 4 (or 5) but our software is built on dotnet core 3.1.
Would it be possible to add this feature, which it seems some of your dotnet engineers already have an implementation of, please?
@JeremyKuhne @carlossanlop

Or could anyone suggest a workaround if not?

Cheers,
Chris

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[reejk]

I ran into the same problem and found a hacky workaround using the MutexSecurity api from System.Threading.AccessControl (Mutex and MemoryMappedFile are both kernel objects).

static void AllowReadWriteAccessToMemoryMappedFile(MemoryMappedFile memoryMappedFile)
{
   const int FILE_MAP_WRITE = 0x0002;
   const int FILE_MAP_READ = 0x0004;

   using var mutex = new Mutex();
   mutex.SafeWaitHandle.Close();
   mutex.SafeWaitHandle = new SafeWaitHandle(memoryMappedFile.SafeMemoryMappedFileHandle.DangerousGetHandle(), false);

   var security = mutex.GetAccessControl();
   security.AddAccessRule(new MutexAccessRule(new SecurityIdentifier(WellKnownSidType.InteractiveSid, null),
      (MutexRights)(FILE_MAP_WRITE | FILE_MAP_READ), AccessControlType.Allow));
   mutex.SetAccessControl(security);
}

Tested on .NET 6 and Windows 11

[ChrisUnityArto]

Thanks Reejk. Good to know!

Unfortunately the product I was working on has been discontinued and I'm working on something else... !

The version of dotnet we were on is quite old now too so I will close this.