A cute yet small MAC policy that provides a simple ACL mechanism to

permit users and groups to bind ports for TCP or UDP, and is intended
to be combined with the recently committed support for
net.inet.ip.portrange.reservedhigh.  The policy is twiddled using
sysctl(8).  To use this module, you will need to compile in MAC
support, and probably set reservedhigh to 0, then twiddle
security.mac.portacl.rules to set things as desired.  This policy
module only restricts ports explicitly bound using bind(), not
implicitly bound ports where the port number is selected by the
IP stack.  It appears to work properly in my local configuration,
but needs more broad testing.

A sample policy might be:

  # sysctl security.mac.portacl.rules="uid:425:tcp:80,uid:425:tcp:79"

This permits uid 425 to bind TCP sockets to ports 79 and 80.  Currently
no distinction is made for incoming vs. outgoing ports with TCP,
although that would probably be easy to add.

Obtained from:	TrustedBSD Project
Sponsored by:	DARPA, Network Associates Laboratories

1 files changed, 485 insertions, 0 deletions

diff --git a/sys/security/mac_portacl/mac_portacl.c b/sys/security/mac_portacl/mac_portacl.c
new file mode 100644
index 0000000..64fa2ad
--- /dev/null
+++ b/sys/security/mac_portacl/mac_portacl.c
@@ -0,0 +1,485 @@
+/*-
+ * Copyright (c) 2003 Networks Associates Technology, Inc.
+ * All rights reserved.
+ *
+ * This software was developed for the FreeBSD Project by Network
+ * Associates Laboratories, the Security Research Division of Network
+ * Associates, Inc. under DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"),
+ * as part of the DARPA CHATS research program.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * $FreeBSD$
+ */
+
+/*
+ * Developed by the TrustedBSD Project.
+ *
+ * Administratively limit access to local UDP/TCP ports for binding purposes.
+ * Intended to be combined with net.inet.ip.portrange.reservedhigh to allow
+ * specific uids and gids to bind specific ports for specific purposes,
+ * while not opening the door to any user replacing an "official" service
+ * while you're restarting it.  This only affects ports explicitly bound by
+ * the user process (either for listen/outgoing socket for TCP, or send/
+ * receive for UDP).  This module will not limit ports bound implicitly for
+ * out-going connections where the process hasn't explicitly selected a port:
+ * these are automatically selected by the IP stack.
+ *
+ * To use this module, security.mac.enforce_socket must be enabled, and
+ * you will probably want to twiddle the net.inet sysctl listed above.
+ * Then use sysctl(8) to modify the rules string:
+ *
+ * # sysctl security.mac.portacl.rules="uid:425:tcp:80,uid:425:tcp:79"
+ *
+ * This ruleset, for example, permits uid 425 to bind TCP ports 80 (http)
+ * and 79 (finger).  User names and group names can't be used directly
+ * because the kernel only knows about uids and gids.
+ */
+
+#include <sys/types.h>
+#include <sys/param.h>
+#include <sys/conf.h>
+#include <sys/domain.h>
+#include <sys/kernel.h>
+#include <sys/libkern.h>
+#include <sys/mac.h>
+#include <sys/malloc.h>
+#include <sys/mount.h>
+#include <sys/proc.h>
+#include <sys/protosw.h>
+#include <sys/queue.h>
+#include <sys/systm.h>
+#include <sys/sysproto.h>
+#include <sys/sysent.h>
+#include <sys/vnode.h>
+#include <sys/file.h>
+#include <sys/sbuf.h>
+#include <sys/socket.h>
+#include <sys/socketvar.h>
+#include <sys/stdint.h>
+#include <sys/sysctl.h>
+
+#include <netinet/in.h>
+
+#include <vm/vm.h>
+
+#include <sys/mac_policy.h>
+
+SYSCTL_DECL(_security_mac);
+
+SYSCTL_NODE(_security_mac, OID_AUTO, portacl, CTLFLAG_RW, 0,
+    "TrustedBSD mac_portacl policy controls");
+
+static int	mac_portacl_enabled = 1;
+SYSCTL_INT(_security_mac_portacl, OID_AUTO, enabled, CTLFLAG_RW,
+    &mac_portacl_enabled, 0, "Enforce portacl policy");
+TUNABLE_INT("security.mac.portacl.enabled", &mac_portacl_enabled);
+
+static int	mac_portacl_suser_exempt = 1;
+SYSCTL_INT(_security_mac_portacl, OID_AUTO, suser_exempt, CTLFLAG_RW,
+    &mac_portacl_suser_exempt, 0, "Privilege permits binding of any port");
+TUNABLE_INT("security.mac.portacl.suser_exempt",
+    &mac_portacl_suser_exempt);
+
+static int	mac_portacl_port_high = 1023;
+SYSCTL_INT(_security_mac_portacl, OID_AUTO, port_high, CTLFLAG_RW,
+    &mac_portacl_port_high, 0, "Highest port to enforce for");
+TUNABLE_INT("security.mac.portacl.port_high", &mac_portacl_port_high);
+
+MALLOC_DEFINE(M_PORTACL, "portacl rule", "Rules for mac_portacl");
+
+#define	MAC_RULE_STRING_LEN	1024
+
+#define	RULE_GID	1
+#define	RULE_UID	2
+#define	RULE_PROTO_TCP	1
+#define	RULE_PROTO_UDP	2
+struct rule {
+	id_t			r_id;
+	int			r_idtype;
+	u_int16_t		r_port;
+	int			r_protocol;
+
+	TAILQ_ENTRY(rule)	r_entries;
+};
+
+#define	GID_STRING	"gid"
+#define	TCP_STRING	"tcp"
+#define	UID_STRING	"uid"
+#define	UDP_STRING	"udp"
+
+/*
+ * Text format for the rule string is that a rule consists of a
+ * comma-seperated list of elements.  Each element is in the form
+ * idtype:id:protocol:portnumber, and constitutes granting of permission
+ * for the specified binding.
+ */
+
+static struct sx			rule_sx;
+static TAILQ_HEAD(rulehead, rule)	rule_head;
+static char				rule_string[MAC_RULE_STRING_LEN];
+
+static void
+toast_rules(struct rulehead *head)
+{
+	struct rule *rule;
+	int i;
+
+	i = 0;
+	for (rule = TAILQ_FIRST(head);
+	     rule != NULL;
+	     rule = TAILQ_NEXT(rule, r_entries))
+		i++;
+
+	while ((rule = TAILQ_FIRST(head)) != NULL) {
+		TAILQ_REMOVE(head, rule, r_entries);
+		free(rule, M_PORTACL);
+	}
+}
+
+/*
+ * Note that there is an inherent race condition in the unload of modules
+ * and access via sysctl.
+ */
+static void
+destroy(struct mac_policy_conf *mpc)
+{
+
+	sx_destroy(&rule_sx);
+	toast_rules(&rule_head);
+}
+
+static void
+init(struct mac_policy_conf *mpc)
+{
+
+	sx_init(&rule_sx, "rule_sx");
+	TAILQ_INIT(&rule_head);
+}
+
+/*
+ * Note: parsing routines are destructive on the passed string.
+ */
+static int
+parse_rule_element(char *element, struct rule **rule)
+{
+	char *idtype, *id, *protocol, *portnumber, *p;
+	struct rule *new;
+	int error;
+
+	error = 0;
+	new = malloc(sizeof(*new), M_PORTACL, M_ZERO | M_WAITOK);
+
+	idtype = strsep(&element, ":");
+	if (idtype == NULL) {
+		error = EINVAL;
+		goto out;
+	}
+	id = strsep(&element, ":");
+	if (id == NULL) {
+		error = EINVAL;
+		goto out;
+	}
+	new->r_id = strtol(id, &p, 10);
+	if (*p != '\0') {
+		error = EINVAL;
+		goto out;
+	}
+	if (strcmp(idtype, UID_STRING) == 0)
+		new->r_idtype = RULE_UID;
+	else if (strcmp(idtype, GID_STRING) == 0)
+		new->r_idtype = RULE_GID;
+	else {
+		error = EINVAL;
+		goto out;
+	}
+	protocol = strsep(&element, ":");
+	if (protocol == NULL) {
+		error = EINVAL;
+		goto out;
+	}
+	if (strcmp(protocol, TCP_STRING) == 0)
+		new->r_protocol = RULE_PROTO_TCP;
+	else if (strcmp(protocol, UDP_STRING) == 0)
+		new->r_protocol = RULE_PROTO_UDP;
+	else {
+		error = EINVAL;
+		goto out;
+	}
+	portnumber = element;
+	if (portnumber == NULL) {
+		error = EINVAL;
+		goto out;
+	}
+	new->r_port = strtol(portnumber, &p, 10);
+	if (*p != '\0') {
+		error = EINVAL;
+		goto out;
+	}
+
+out:
+	if (error != 0) {
+		free(new, M_PORTACL);
+		*rule = NULL;
+	} else
+		*rule = new;
+	return (error);
+}
+
+static int
+parse_rules(char *string, struct rulehead *head)
+{
+	struct rule *new;
+	char *element;
+	int error;
+
+	error = 0;
+	while ((element = strsep(&string, ",")) != NULL) {
+		if (strlen(element) == 0)
+			continue;
+		error = parse_rule_element(element, &new);
+		if (error)
+			goto out;
+		TAILQ_INSERT_TAIL(head, new, r_entries);
+	}
+out:
+	if (error != 0)
+		toast_rules(head);
+	return (error);
+}
+
+#if 0
+static void
+rule_printf(struct sbuf *sb, struct rule *rule)
+{
+	const char *idtype, *protocol;
+
+	switch(rule->r_idtype) {
+	case RULE_GID:
+		idtype = GID_STRING;
+		break;
+	case RULE_UID:
+		idtype = UID_STRING;
+		break;
+	default:
+		panic("rule_printf: unknown idtype (%d)\n", rule->r_idtype);
+	}
+
+	switch (rule->r_protocol) {
+	case RULE_PROTO_TCP:
+		protocol = TCP_STRING;
+		break;
+	case RULE_PROTO_UDP:
+		protocol = UDP_STRING;
+		break;
+	default:
+		panic("rule_printf: unknown protocol (%d)\n",
+		    rule->r_protocol);
+	}
+	sbuf_printf(sb, "%s:%jd:%s:%d", idtype, (intmax_t)rule->r_id,
+	    protocol, rule->r_port);
+}
+
+static char *
+rules_to_string(void)
+{
+	struct rule *rule;
+	struct sbuf *sb;
+	int needcomma;
+	char *temp;
+
+	sb = sbuf_new(NULL, NULL, 0, SBUF_AUTOEXTEND);
+	needcomma = 0;
+	sx_slock(&rule_sx);
+	for (rule = TAILQ_FIRST(&rule_head); rule != NULL;
+	    rule = TAILQ_NEXT(rule, r_entries)) {
+		if (!needcomma)
+			needcomma = 1;
+		else
+			sbuf_printf(sb, ",");
+		rule_printf(sb, rule);
+	}
+	sx_sunlock(&rule_sx);
+	sbuf_finish(sb);
+	temp = strdup(sbuf_data(sb), M_PORTACL);
+	sbuf_delete(sb);
+	return (temp);
+}
+#endif
+
+/*
+ * Note: due to races, there is not a single serializable order
+ * between parallel calls to the sysctl.
+ */
+static int
+sysctl_rules(SYSCTL_HANDLER_ARGS)
+{
+	char *string, *copy_string, *new_string;
+	struct rulehead head, save_head;
+	struct rule *rule;
+	int error;
+
+	new_string = NULL;
+	if (req->newptr == NULL) {
+		new_string = malloc(MAC_RULE_STRING_LEN, M_PORTACL,
+		    M_WAITOK | M_ZERO);
+		strcpy(new_string, rule_string);
+		string = new_string;
+	} else
+		string = rule_string;
+
+	error = sysctl_handle_string(oidp, string, MAC_RULE_STRING_LEN, req);
+	if (error)
+		goto out;
+
+	if (req->newptr != NULL) {
+		copy_string = strdup(string, M_PORTACL);
+		TAILQ_INIT(&head);
+		error = parse_rules(copy_string, &head);
+		free(copy_string, M_PORTACL);
+		if (error)
+			goto out;
+
+		TAILQ_INIT(&save_head);
+		sx_xlock(&rule_sx);
+		/*
+		 * XXX: Unfortunately, TAILQ doesn't yet have a supported
+		 * assignment operator to copy one queue to another, due
+	 	 * to a self-referential pointer in the tailq header.
+		 * For now, do it the old-fashioned way.
+		 */
+		while ((rule = TAILQ_FIRST(&rule_head)) != NULL) {
+			TAILQ_REMOVE(&rule_head, rule, r_entries);
+			TAILQ_INSERT_HEAD(&save_head, rule, r_entries);
+		}
+		while ((rule = TAILQ_FIRST(&head)) != NULL) {
+			TAILQ_REMOVE(&head, rule, r_entries);
+			TAILQ_INSERT_HEAD(&rule_head, rule, r_entries);
+		}
+		strcpy(rule_string, string);
+		sx_xunlock(&rule_sx);
+		toast_rules(&save_head);
+	}
+out:
+	if (new_string != NULL)
+		free(new_string, M_PORTACL);
+	return (error);
+}
+
+SYSCTL_PROC(_security_mac_portacl, OID_AUTO, rules,
+       CTLTYPE_STRING|CTLFLAG_RW, 0, 0, sysctl_rules, "A", "Rules");
+
+static int
+rules_check(struct ucred *cred, int family, int type, u_int16_t port)
+{
+	struct rule *rule;
+	int error;
+
+#if 0
+	printf("Check requested for euid %d, family %d, type %d, port %d\n",
+	    cred->cr_uid, family, type, port);
+#endif
+
+	if (port > mac_portacl_port_high)
+		return (0);
+
+	error = EPERM;
+	sx_slock(&rule_sx);
+	for (rule = TAILQ_FIRST(&rule_head);
+	    rule != NULL;
+	    rule = TAILQ_NEXT(rule, r_entries)) {
+		if (type == SOCK_DGRAM && rule->r_protocol != RULE_PROTO_UDP)
+			continue;
+		if (type == SOCK_STREAM && rule->r_protocol != RULE_PROTO_TCP)
+			continue;
+		if (port != rule->r_port)
+			continue;
+		if (rule->r_idtype == RULE_UID) {
+			if (cred->cr_uid == rule->r_id) {
+				error = 0;
+				break;
+			}
+		} else if (rule->r_idtype == RULE_GID) {
+			if (cred->cr_gid == rule->r_id) {
+				error = 0;
+				break;
+			} else if (groupmember(rule->r_id, cred)) {
+				error = 0;
+				break;
+			}
+		} else
+			panic("rules_check: unknown rule type %d",
+			    rule->r_idtype);
+	}
+	sx_sunlock(&rule_sx);
+
+	if (error != 0 && mac_portacl_suser_exempt != 0)
+		error = suser_cred(cred, 0);
+
+	return (error);
+}
+
+/*
+ * Note, this only limits the ability to explicitly bind a port, it
+ * doesn't limit implicitly bound ports for outgoing connections where
+ * the source port is left up to the IP stack to determine automatically.
+ */
+static int
+check_socket_bind(struct ucred *cred, struct socket *so,
+    struct label *socketlabel, struct sockaddr *sockaddr)
+{
+	struct sockaddr_in *sin;
+	int family, type;
+	u_int16_t port;
+
+	/* Only interested in IPv4 and IPv6 sockets. */
+	if (so->so_proto->pr_domain->dom_family != PF_INET &&
+	    so->so_proto->pr_domain->dom_family != PF_INET6)
+		return (0);
+
+	/* Currently, we don't attempt to deal with SOCK_RAW, etc. */
+	if (so->so_type != SOCK_DGRAM &&
+	    so->so_type != SOCK_STREAM)
+		return (0);
+
+	/* Reject addresses we don't understand; fail closed. */
+	if (sockaddr->sa_family != AF_INET &&
+	    sockaddr->sa_family != AF_INET6)
+		return (EINVAL);
+
+	family = so->so_proto->pr_domain->dom_family;
+	type = so->so_type;
+	sin = (struct sockaddr_in *) sockaddr;
+	port = ntohs(sin->sin_port);
+
+	return (rules_check(cred, family, type, port));
+}
+
+static struct mac_policy_ops mac_portacl_ops =
+{
+	.mpo_destroy = destroy,
+	.mpo_init = init,
+	.mpo_check_socket_bind = check_socket_bind,
+};
+
+MAC_POLICY_SET(&mac_portacl_ops, trustedbsd_mac_portacl,
+    "TrustedBSD MAC/portacl", MPC_LOADTIME_FLAG_UNLOADOK, NULL);