Userfaultfd in unprivileged contexts could be potentially very useful. We'd like to harden userfaultfd to make such unprivileged use less risky. This patch series allows SELinux to manage userfaultfd file descriptors (via a new flag, for compatibility with existing code) and allows administrators to limit userfaultfd to servicing user-mode faults, increasing the difficulty of using userfaultfd in exploit chains invoking delaying kernel faults. A new anon_inodes interface allows callers to opt into SELinux management of anonymous file objects. In this mode, anon_inodes creates new ephemeral inodes for anonymous file objects instead of reusing a singleton dummy inode. A new LSM hook gives security modules an opportunity to configure and veto these ephemeral inodes. Existing anon_inodes users must opt into the new functionality. Daniel Colascione (7): Add a new flags-accepting interface for anonymous inodes Add a concept of a "secure" anonymous file Add a UFFD_SECURE flag to the userfaultfd API. Teach SELinux about a new userfaultfd class Let userfaultfd opt out of handling kernel-mode faults Allow users to require UFFD_SECURE Add a new sysctl for limiting userfaultfd to user mode faults Documentation/admin-guide/sysctl/vm.rst | 19 +++++- fs/anon_inodes.c | 89 +++++++++++++++++-------- fs/userfaultfd.c | 47 +++++++++++-- include/linux/anon_inodes.h | 27 ++++++-- include/linux/lsm_hooks.h | 8 +++ include/linux/security.h | 2 + include/linux/userfaultfd_k.h | 3 + include/uapi/linux/userfaultfd.h | 14 ++++ kernel/sysctl.c | 9 +++ security/security.c | 8 +++ security/selinux/hooks.c | 68 +++++++++++++++++++ security/selinux/include/classmap.h | 2 + 12 files changed, 256 insertions(+), 40 deletions(-) -- 2.23.0.700.g56cf767bdb-goog
