Re: [PATCH v14 3/4] selinux: teach SELinux about anonymous inodes

From: Daniel Colascione <redacted>

This change uses the anon_inodes and LSM infrastructure introduced in
the previous patches to give SELinux the ability to control
anonymous-inode files that are created using the new
anon_inode_getfd_secure() function.

A SELinux policy author detects and controls these anonymous inodes by
adding a name-based type_transition rule that assigns a new security
type to anonymous-inode files created in some domain. The name used
for the name-based transition is the name associated with the
anonymous inode for file listings --- e.g., "[userfaultfd]" or
"[perf_event]".

Example:

type uffd_t;
type_transition sysadm_t sysadm_t : anon_inode uffd_t "[userfaultfd]";
allow sysadm_t uffd_t:anon_inode { create };

(The next patch in this series is necessary for making userfaultfd
support this new interface.  The example above is just
for exposition.)

Signed-off-by: Daniel Colascione <redacted>
Signed-off-by: Lokesh Gidra <redacted>
---
 security/selinux/hooks.c            | 59 +++++++++++++++++++++++++++++
 security/selinux/include/classmap.h |  2 +
 2 files changed, 61 insertions(+)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 644b17ec9e63..8b4e155b2930 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c

@@ -2934,6 +2933,63 @@ static int selinux_inode_init_security(struct inode *inode, struct inode *dir,
        return 0;
 }

+static int selinux_inode_init_security_anon(struct inode *inode,
+                                           const struct qstr *name,
+                                           const struct inode *context_inode)
+{
+       const struct task_security_struct *tsec = selinux_cred(current_cred());
+       struct common_audit_data ad;
+       struct inode_security_struct *isec;
+       int rc;
+
+       if (unlikely(!selinux_initialized(&selinux_state)))
+               return 0;
+
+       isec = selinux_inode(inode);
+
+       /*
+        * We only get here once per ephemeral inode.  The inode has
+        * been initialized via inode_alloc_security but is otherwise
+        * untouched.
+        */
+       isec->initialized = LABEL_INITIALIZED;
+       isec->sclass = SECCLASS_ANON_INODE;
+
+       if (context_inode) {
+               struct inode_security_struct *context_isec =
+                       selinux_inode(context_inode);
+               if (context_isec->initialized != LABEL_INITIALIZED)
+                       return -EACCES;
+               if (context_isec->sclass != SECCLASS_ANON_INODE) {
+                       pr_err("SELinux:  initializing anonymous inode with non-anonymous inode");
+                       return -EACCES;
+               }