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 and in the future, other kinds of anonymous-inode-based file descriptor. SELinux policy authors can apply policy types to anonymous inodes by providing name-based transition rules keyed off the anonymous inode internal name ( "[userfaultfd]" in the case of userfaultfd(2) file descriptors) and applying policy to the new SIDs thus produced. Inside the kernel, a pair of new anon_inodes interface, anon_inode_getfile_secure and anon_inode_getfd_secure, allow callers to opt into this SELinux management. In this new "secure" mode, anon_inodes creates new ephemeral inodes for anonymous file objects instead of reusing the normal anon_inodes singleton dummy inode. A new LSM hook gives security modules an opportunity to configure and veto these ephemeral inodes. This patch series is one of two fork of [1] and is an alternative to [2]. The primary difference between the two patch series is that this partch series creates a unique inode for each "secure" anonymous inode, while the other patch series ([2]) continues using the singleton dummy anonymous inode and adds a way to attach SELinux security information directly to file objects. I prefer the approach in this patch series because 1) it's a smaller patch than [2], and 2) it produces a more regular security architecture: in this patch series, secure anonymous inodes aren't S_PRIVATE and they maintain the SELinux property that the label for a file is in its inode. We do need an additional inode per anonymous file, but per-struct-file inode creation doesn't seem to be a problem for pipes and sockets. The previous version of this feature ([1]) created a new SELinux security class for userfaultfd file descriptors. This version adopts the generic transition-based approach of [2]. This patch series also differs from [2] in that it doesn't affect all anonymous inodes right away --- instead requiring anon_inodes callers to opt in --- but this difference isn't one of basic approach. The important question to resolve is whether we should be creating new inodes or enhancing per-file data. [1] https://lore.kernel.org/lkml/20200211225547.235083-1-dancol@xxxxxxxxxx/ [2] https://lore.kernel.org/linux-fsdevel/20200213194157.5877-1-sds@xxxxxxxxxxxxx/ Daniel Colascione (3): Add a new LSM-supporting anonymous inode interface Teach SELinux about anonymous inodes Wire UFFD up to SELinux fs/anon_inodes.c | 196 ++++++++++++++++++++++++++++-------- fs/userfaultfd.c | 34 +++++-- include/linux/anon_inodes.h | 13 +++ include/linux/lsm_hooks.h | 9 ++ include/linux/security.h | 4 + security/security.c | 10 ++ security/selinux/hooks.c | 57 +++++++++++ 7 files changed, 274 insertions(+), 49 deletions(-) -- 2.25.0.265.gbab2e86ba0-goog
