On Tue, 2004-11-09 at 05:58, Park Lee wrote:
> In flask, as we know, sockets effectively serve as communication
> proxies for processes in the Flask control model. Consequently,
> sockets are labeled with the label of the creating process by default.
> Messages are associated with both the label of their sending socket
> and a separate message label. By default, this message label is the
> same as the sending socket label.
> Then how can we get the security context of socket and message
> respectively in linux kernel space and user space respectively (i.e.
> what functions and commands could we use to achieve our goal)?
> And is messages here refer to packages in network?

In the kernel, you can obtain the security context of a socket via the security field of its associated inode. Look at socket_has_perm() and selinux_socket_sock_rcv_skb() in security/selinux/hooks.c for examples. Unix domain sockets can also use the sk_security field in the struct sock for security state (e.g. peer SID), but INET sockets cannot safely do so at present. Remember that most of the LSM networking security fields and hooks were rejected by the mainline kernel, so only limited support exists in the current SELinux and there is no message labeling at all.

Since sys_security was rejected by the mainline kernel, the extended socket API of SELinux is not presently supported; we will ultimately have to revisit it in the future when we have better motivating examples of real applications that use it. While fgetfilecon()->fgetxattr() could conceivably export the security context of a local socket, that would require implementing a fake xattr handler for the socket code; alternative would be to implement it via getsockopt(). There is a getpeercon(3) function in libselinux that allows you to get the context of a peer for a Unix domain stream socket; this is internally implemented via getsockopt().

-- 
Stephen Smalley <sds@epoch.ncsc.mil>
National Security Agency


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