[PATCH 4/5] selinux: Enhance selinux to always ignore private inodes.

[ebiederm@xmission.com (Eric W. Biederman)]

From: Stephen Smalley <sds@tycho.nsa.gov>

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>

---
 security/selinux/hooks.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index de16b9f..ff9fccc 100644
--- a/security/selinux/hooks.c
+++ b/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;
 
--