Memfd Examples Save

Introduction

This is a small server and client application for prototyping the new memfd_create(2) Linux system call.

Memfd is a simple memory sharing mechanism, added by the systemd/kdbus developers, to share pages between processes in an anonymous, no global registry needed, no mount-point required, relatively secure, manner. Check the references at the bottom of this page for primary documentation.

Internal details

Server creates a classic Unix domain socket, and waits for clients to connect.

Upon a client connection, server creates a memfd region and fill it with a unique message. The file descriptor for this memory region is then sealed and passed to the client using Unix domain sockets file-descriptor passing mechanisms.

On the client side, upon connecting with the server, it recreives the passed memfd file descriptor. Afterwards, the client tries to break the SHRINK, WRITE, and SEAL memfd seals added by the server.

If everything goes as planned, the client can go and read the server-sent message by mmap()-ing the passed file descriptor. This form of communication is both zero-copy, and hopefully secure-enough, for zero-trust IPC applications.

Requirements

• Linux Kernel 3.17 or higher
• Header files for such a kernel
  • Debian/Ubuntu: sudo apt-get install linux-headers-$(uname -r)
  • Redhat/Fedora: sudo yum -y kernel-headers-$(uname -r)
  • Arch Linux: sudo pacman -S linux-headers

References:

• On memfd_create(2), David Herrman (memfd author)
• memfd_create(2) manpage
• The Linux Programming Interface, Section 61.13.3 "Passing File Descriptors"
• FD Passing for DRI.Next, Keith Packard (Xorg maintainer)