[PATCH] selinux: enhance selinux to always ignore private inodes

Hmmm...turns out to not be quite enough, as the /proc/sys inodes aren't truly
private to the fs, so we can run into them in a variety of security hooks
beyond just the inode hooks, such as security_file_permission (when reading
and writing them via the vfs helpers), security_sb_mount (when mounting other
filesystems on directories in proc like binfmt_misc), and deeper within the
security module itself (as in flush_unauthorized_files upon inheritance across
execve).  So I think we have to add an IS_PRIVATE() guard within SELinux, as
below.  Note however that the use of the private flag here could be confusing,
as these inodes are _not_ private to the fs, are exposed to userspace, and
security modules must implement the sysctl hook to get any access control over
them.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

security/selinux/hooks.c

@@ -1077,6 +1077,9 @@ static int inode_has_perm(struct task_struct *tsk,
 	struct inode_security_struct *isec;
 	struct avc_audit_data ad;
 
+	if (unlikely (IS_PRIVATE (inode)))
+		return 0;
+
 	tsec = tsk->security;
 	isec = inode->i_security;