[SECURITY]: TCP/UDP getpeersec

This patch implements an application of the LSM-IPSec networking
controls whereby an application can determine the label of the
security association its TCP or UDP sockets are currently connected to
via getsockopt and the auxiliary data mechanism of recvmsg.

Patch purpose:

This patch enables a security-aware application to retrieve the
security context of an IPSec security association a particular TCP or
UDP socket is using.  The application can then use this security
context to determine the security context for processing on behalf of
the peer at the other end of this connection.  In the case of UDP, the
security context is for each individual packet.  An example
application is the inetd daemon, which could be modified to start
daemons running at security contexts dependent on the remote client.

Patch design approach:

- Design for TCP
The patch enables the SELinux LSM to set the peer security context for
a socket based on the security context of the IPSec security
association.  The application may retrieve this context using
getsockopt.  When called, the kernel determines if the socket is a
connected (TCP_ESTABLISHED) TCP socket and, if so, uses the dst_entry
cache on the socket to retrieve the security associations.  If a
security association has a security context, the context string is
returned, as for UNIX domain sockets.

- Design for UDP
Unlike TCP, UDP is connectionless.  This requires a somewhat different
API to retrieve the peer security context.  With TCP, the peer
security context stays the same throughout the connection, thus it can
be retrieved at any time between when the connection is established
and when it is torn down.  With UDP, each read/write can have
different peer and thus the security context might change every time.
As a result the security context retrieval must be done TOGETHER with
the packet retrieval.

The solution is to build upon the existing Unix domain socket API for
retrieving user credentials.  Linux offers the API for obtaining user
credentials via ancillary messages (i.e., out of band/control messages
that are bundled together with a normal message).

Patch implementation details:

- Implementation for TCP
The security context can be retrieved by applications using getsockopt
with the existing SO_PEERSEC flag.  As an example (ignoring error
checking):

getsockopt(sockfd, SOL_SOCKET, SO_PEERSEC, optbuf, &optlen);
printf("Socket peer context is: %s\n", optbuf);

The SELinux function, selinux_socket_getpeersec, is extended to check
for labeled security associations for connected (TCP_ESTABLISHED ==
sk->sk_state) TCP sockets only.  If so, the socket has a dst_cache of
struct dst_entry values that may refer to security associations.  If
these have security associations with security contexts, the security
context is returned.

getsockopt returns a buffer that contains a security context string or
the buffer is unmodified.

- Implementation for UDP
To retrieve the security context, the application first indicates to
the kernel such desire by setting the IP_PASSSEC option via
getsockopt.  Then the application retrieves the security context using
the auxiliary data mechanism.

An example server application for UDP should look like this:

toggle = 1;
toggle_len = sizeof(toggle);

setsockopt(sockfd, SOL_IP, IP_PASSSEC, &toggle, &toggle_len);
recvmsg(sockfd, &msg_hdr, 0);
if (msg_hdr.msg_controllen > sizeof(struct cmsghdr)) {
    cmsg_hdr = CMSG_FIRSTHDR(&msg_hdr);
    if (cmsg_hdr->cmsg_len <= CMSG_LEN(sizeof(scontext)) &&
        cmsg_hdr->cmsg_level == SOL_IP &&
        cmsg_hdr->cmsg_type == SCM_SECURITY) {
        memcpy(&scontext, CMSG_DATA(cmsg_hdr), sizeof(scontext));
    }
}

ip_setsockopt is enhanced with a new socket option IP_PASSSEC to allow
a server socket to receive security context of the peer.  A new
ancillary message type SCM_SECURITY.

When the packet is received we get the security context from the
sec_path pointer which is contained in the sk_buff, and copy it to the
ancillary message space.  An additional LSM hook,
selinux_socket_getpeersec_udp, is defined to retrieve the security
context from the SELinux space.  The existing function,
selinux_socket_getpeersec does not suit our purpose, because the
security context is copied directly to user space, rather than to
kernel space.

Testing:

We have tested the patch by setting up TCP and UDP connections between
applications on two machines using the IPSec policies that result in
labeled security associations being built.  For TCP, we can then
extract the peer security context using getsockopt on either end.  For
UDP, the receiving end can retrieve the security context using the
auxiliary data mechanism of recvmsg.

Signed-off-by: Catherine Zhang <cxzhang@watson.ibm.com>
Acked-by: James Morris <jmorris@namei.org>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/in.h

@@ -72,6 +72,7 @@ struct in_addr {
 #define IP_FREEBIND	15
 #define IP_IPSEC_POLICY	16
 #define IP_XFRM_POLICY	17
+#define IP_PASSSEC	18
 
 /* BSD compatibility */
 #define IP_RECVRETOPTS	IP_RETOPTS

include/linux/security.h

@@ -1286,7 +1286,8 @@ struct security_operations {
 	int (*socket_setsockopt) (struct socket * sock, int level, int optname);
 	int (*socket_shutdown) (struct socket * sock, int how);
 	int (*socket_sock_rcv_skb) (struct sock * sk, struct sk_buff * skb);
-	int (*socket_getpeersec) (struct socket *sock, char __user *optval, int __user *optlen, unsigned len);
+	int (*socket_getpeersec_stream) (struct socket *sock, char __user *optval, int __user *optlen, unsigned len);
+	int (*socket_getpeersec_dgram) (struct sk_buff *skb, char **secdata, u32 *seclen);
 	int (*sk_alloc_security) (struct sock *sk, int family, gfp_t priority);
 	void (*sk_free_security) (struct sock *sk);
 	unsigned int (*sk_getsid) (struct sock *sk, struct flowi *fl, u8 dir);
@@ -2741,10 +2742,16 @@ static inline int security_sock_rcv_skb (struct sock * sk,
 	return security_ops->socket_sock_rcv_skb (sk, skb);
 }
 
-static inline int security_socket_getpeersec(struct socket *sock, char __user *optval,
-					     int __user *optlen, unsigned len)
+static inline int security_socket_getpeersec_stream(struct socket *sock, char __user *optval,
+						    int __user *optlen, unsigned len)
 {
-	return security_ops->socket_getpeersec(sock, optval, optlen, len);
+	return security_ops->socket_getpeersec_stream(sock, optval, optlen, len);
+}
+
+static inline int security_socket_getpeersec_dgram(struct sk_buff *skb, char **secdata,
+						   u32 *seclen)
+{
+	return security_ops->socket_getpeersec_dgram(skb, secdata, seclen);
 }
 
 static inline int security_sk_alloc(struct sock *sk, int family, gfp_t priority)
@@ -2863,8 +2870,14 @@ static inline int security_sock_rcv_skb (struct sock * sk,
 	return 0;
 }
 
-static inline int security_socket_getpeersec(struct socket *sock, char __user *optval,
-					     int __user *optlen, unsigned len)
+static inline int security_socket_getpeersec_stream(struct socket *sock, char __user *optval,
+						    int __user *optlen, unsigned len)
+{
+	return -ENOPROTOOPT;
+}
+
+static inline int security_socket_getpeersec_dgram(struct sk_buff *skb, char **secdata,
+						   u32 *seclen)
 {
 	return -ENOPROTOOPT;
 }

include/linux/socket.h

@@ -150,6 +150,7 @@ __KINLINE struct cmsghdr * cmsg_nxthdr (struct msghdr *__msg, struct cmsghdr *__
 
 #define	SCM_RIGHTS	0x01		/* rw: access rights (array of int) */
 #define SCM_CREDENTIALS 0x02		/* rw: struct ucred		*/
+#define SCM_SECURITY	0x03		/* rw: security label		*/
 
 struct ucred {
 	__u32	pid;

net/core/sock.c

@@ -616,7 +616,7 @@ int sock_getsockopt(struct socket *sock, int level, int optname,
 			break;
 
 		case SO_PEERSEC:
-			return security_socket_getpeersec(sock, optval, optlen, len);
+			return security_socket_getpeersec_stream(sock, optval, optlen, len);
 
 		default:
 			return(-ENOPROTOOPT);

net/ipv4/ip_sockglue.c

@@ -50,6 +50,7 @@
 #define IP_CMSG_TOS		4
 #define IP_CMSG_RECVOPTS	8
 #define IP_CMSG_RETOPTS		16
+#define IP_CMSG_PASSSEC		32
 
 /*
  *	SOL_IP control messages.
@@ -109,6 +110,19 @@ static void ip_cmsg_recv_retopts(struct msghdr *msg, struct sk_buff *skb)
 	put_cmsg(msg, SOL_IP, IP_RETOPTS, opt->optlen, opt->__data);
 }
 
+static void ip_cmsg_recv_security(struct msghdr *msg, struct sk_buff *skb)
+{
+	char *secdata;
+	u32 seclen;
+	int err;
+
+	err = security_socket_getpeersec_dgram(skb, &secdata, &seclen);
+	if (err)
+		return;
+
+	put_cmsg(msg, SOL_IP, SCM_SECURITY, seclen, secdata);
+}
+
 
 void ip_cmsg_recv(struct msghdr *msg, struct sk_buff *skb)
 {
@@ -138,6 +152,11 @@ void ip_cmsg_recv(struct msghdr *msg, struct sk_buff *skb)
 
 	if (flags & 1)
 		ip_cmsg_recv_retopts(msg, skb);
+	if ((flags>>=1) == 0)
+		return;
+
+	if (flags & 1)
+		ip_cmsg_recv_security(msg, skb);
 }
 
 int ip_cmsg_send(struct msghdr *msg, struct ipcm_cookie *ipc)
@@ -393,7 +412,8 @@ int ip_setsockopt(struct sock *sk, int level, int optname, char __user *optval,
 			    (1<<IP_RETOPTS) | (1<<IP_TOS) | 
 			    (1<<IP_TTL) | (1<<IP_HDRINCL) | 
 			    (1<<IP_MTU_DISCOVER) | (1<<IP_RECVERR) | 
-			    (1<<IP_ROUTER_ALERT) | (1<<IP_FREEBIND))) || 
+			    (1<<IP_ROUTER_ALERT) | (1<<IP_FREEBIND) |
+			    (1<<IP_PASSSEC))) ||
 				optname == IP_MULTICAST_TTL || 
 				optname == IP_MULTICAST_LOOP) { 
 		if (optlen >= sizeof(int)) {
@@ -478,6 +498,12 @@ int ip_setsockopt(struct sock *sk, int level, int optname, char __user *optval,
 			else
 				inet->cmsg_flags &= ~IP_CMSG_RETOPTS;
 			break;
+		case IP_PASSSEC:
+			if (val)
+				inet->cmsg_flags |= IP_CMSG_PASSSEC;
+			else
+				inet->cmsg_flags &= ~IP_CMSG_PASSSEC;
+			break;
 		case IP_TOS:	/* This sets both TOS and Precedence */
 			if (sk->sk_type == SOCK_STREAM) {
 				val &= ~3;
@@ -932,6 +958,9 @@ int ip_getsockopt(struct sock *sk, int level, int optname, char __user *optval,
 		case IP_RETOPTS:
 			val = (inet->cmsg_flags & IP_CMSG_RETOPTS) != 0;
 			break;
+		case IP_PASSSEC:
+			val = (inet->cmsg_flags & IP_CMSG_PASSSEC) != 0;
+			break;
 		case IP_TOS:
 			val = inet->tos;
 			break;

security/dummy.c

@@ -763,8 +763,14 @@ static int dummy_socket_sock_rcv_skb (struct sock *sk, struct sk_buff *skb)
 	return 0;
 }
 
-static int dummy_socket_getpeersec(struct socket *sock, char __user *optval,
-				   int __user *optlen, unsigned len)
+static int dummy_socket_getpeersec_stream(struct socket *sock, char __user *optval,
+					  int __user *optlen, unsigned len)
+{
+	return -ENOPROTOOPT;
+}
+
+static int dummy_socket_getpeersec_dgram(struct sk_buff *skb, char **secdata,
+					 u32 *seclen)
 {
 	return -ENOPROTOOPT;
 }

security/selinux/hooks.c

@@ -3318,24 +3318,38 @@ static int selinux_socket_sock_rcv_skb(struct sock *sk, struct sk_buff *skb)
 	return err;
 }
 
-static int selinux_socket_getpeersec(struct socket *sock, char __user *optval,
-				     int __user *optlen, unsigned len)
+static int selinux_socket_getpeersec_stream(struct socket *sock, char __user *optval,
+					    int __user *optlen, unsigned len)
 {
 	int err = 0;
 	char *scontext;
 	u32 scontext_len;
 	struct sk_security_struct *ssec;
 	struct inode_security_struct *isec;
+	u32 peer_sid = 0;
 
 	isec = SOCK_INODE(sock)->i_security;
-	if (isec->sclass != SECCLASS_UNIX_STREAM_SOCKET) {
+
+	/* if UNIX_STREAM check peer_sid, if TCP check dst for labelled sa */
+	if (isec->sclass == SECCLASS_UNIX_STREAM_SOCKET) {
+		ssec = sock->sk->sk_security;
+		peer_sid = ssec->peer_sid;
+	}
+	else if (isec->sclass == SECCLASS_TCP_SOCKET) {
+		peer_sid = selinux_socket_getpeer_stream(sock->sk);
+
+		if (peer_sid == SECSID_NULL) {
+			err = -ENOPROTOOPT;
+			goto out;
+		}
+	}
+	else {
 		err = -ENOPROTOOPT;
 		goto out;
 	}
 
-	ssec = sock->sk->sk_security;
-	
-	err = security_sid_to_context(ssec->peer_sid, &scontext, &scontext_len);
+	err = security_sid_to_context(peer_sid, &scontext, &scontext_len);
+
 	if (err)
 		goto out;
 
@@ -3356,6 +3370,23 @@ static int selinux_socket_getpeersec(struct socket *sock, char __user *optval,
 	return err;
 }
 
+static int selinux_socket_getpeersec_dgram(struct sk_buff *skb, char **secdata, u32 *seclen)
+{
+	int err = 0;
+	u32 peer_sid = selinux_socket_getpeer_dgram(skb);
+
+	if (peer_sid == SECSID_NULL)
+		return -EINVAL;
+
+	err = security_sid_to_context(peer_sid, secdata, seclen);
+	if (err)
+		return err;
+
+	return 0;
+}
+
+
+
 static int selinux_sk_alloc_security(struct sock *sk, int family, gfp_t priority)
 {
 	return sk_alloc_security(sk, family, priority);
@@ -4344,7 +4375,8 @@ static struct security_operations selinux_ops = {
 	.socket_setsockopt =		selinux_socket_setsockopt,
 	.socket_shutdown =		selinux_socket_shutdown,
 	.socket_sock_rcv_skb =		selinux_socket_sock_rcv_skb,
-	.socket_getpeersec =		selinux_socket_getpeersec,
+	.socket_getpeersec_stream =	selinux_socket_getpeersec_stream,
+	.socket_getpeersec_dgram =	selinux_socket_getpeersec_dgram,
 	.sk_alloc_security =		selinux_sk_alloc_security,
 	.sk_free_security =		selinux_sk_free_security,
 	.sk_getsid = 			selinux_sk_getsid_security,

security/selinux/include/xfrm.h

@@ -39,6 +39,8 @@ static inline u32 selinux_no_sk_sid(struct flowi *fl)
 #ifdef CONFIG_SECURITY_NETWORK_XFRM
 int selinux_xfrm_sock_rcv_skb(u32 sid, struct sk_buff *skb);
 int selinux_xfrm_postroute_last(u32 isec_sid, struct sk_buff *skb);
+u32 selinux_socket_getpeer_stream(struct sock *sk);
+u32 selinux_socket_getpeer_dgram(struct sk_buff *skb);
 #else
 static inline int selinux_xfrm_sock_rcv_skb(u32 isec_sid, struct sk_buff *skb)
 {

security/selinux/xfrm.c

@@ -224,6 +224,74 @@ void selinux_xfrm_state_free(struct xfrm_state *x)
 		kfree(ctx);
 }
 
+/*
+ * SELinux internal function to retrieve the context of a connected
+ * (sk->sk_state == TCP_ESTABLISHED) TCP socket based on its security
+ * association used to connect to the remote socket.
+ *
+ * Retrieve via getsockopt SO_PEERSEC.
+ */
+u32 selinux_socket_getpeer_stream(struct sock *sk)
+{
+	struct dst_entry *dst, *dst_test;
+	u32 peer_sid = SECSID_NULL;
+
+	if (sk->sk_state != TCP_ESTABLISHED)
+		goto out;
+
+	dst = sk_dst_get(sk);
+	if (!dst)
+		goto out;
+
+ 	for (dst_test = dst; dst_test != 0;
+      	     dst_test = dst_test->child) {
+		struct xfrm_state *x = dst_test->xfrm;
+
+ 		if (x && selinux_authorizable_xfrm(x)) {
+	 	 	struct xfrm_sec_ctx *ctx = x->security;
+			peer_sid = ctx->ctx_sid;
+			break;
+		}
+	}
+	dst_release(dst);
+
+out:
+	return peer_sid;
+}
+
+/*
+ * SELinux internal function to retrieve the context of a UDP packet
+ * based on its security association used to connect to the remote socket.
+ *
+ * Retrieve via setsockopt IP_PASSSEC and recvmsg with control message
+ * type SCM_SECURITY.
+ */
+u32 selinux_socket_getpeer_dgram(struct sk_buff *skb)
+{
+	struct sec_path *sp;
+
+	if (skb == NULL)
+		return SECSID_NULL;
+
+	if (skb->sk->sk_protocol != IPPROTO_UDP)
+		return SECSID_NULL;
+
+	sp = skb->sp;
+	if (sp) {
+		int i;
+
+		for (i = sp->len-1; i >= 0; i--) {
+			struct xfrm_state *x = sp->x[i].xvec;
+			if (selinux_authorizable_xfrm(x)) {
+				struct xfrm_sec_ctx *ctx = x->security;
+				return ctx->ctx_sid;
+			}
+		}
+	}
+
+	return SECSID_NULL;
+}
+
 /*
  * LSM hook that controls access to unlabelled packets.  If
  * a xfrm_state is authorizable (defined by macro) then it was