privsep: Add support for priviledge separation

Not enabled by default - enable with ./configure --enable-privsep
Requires a user added to the system - default _dhcpcd

Several processes will be spawned off the main state engine:
a privileged actioneer and a generic network proxy.
Only the privileged actioneer process will retain root permissions.

When required, the privileged actioneer will also spawn
BPF listeners for BOOTP (DHCP) and ARP.
The BOOTP BPF listener should be a short lived process.
On kernels with RFC 5227 support, the ARP BPF listener will only
be used for ARPing and announcing a preferred address and will
also be a short lived process.

When not running in master mode, an address listener will be
spawned for each address (with the exception of RA dervived addresses)
dhcpcd cares about.

TODO:
 * Solaris support.
 * ARP BPF address filtering.

1 files changed, 567 insertions, 0 deletions

diff --git a/src/privsep-inet.c b/src/privsep-inet.c
new file mode 100644
index 00000000..1b107889
--- /dev/null
+++ b/src/privsep-inet.c
@@ -0,0 +1,567 @@
+/* SPDX-License-Identifier: BSD-2-Clause */
+/*
+ * Priviledge Separation for dhcpcd, network proxy
+ * Copyright (c) 2006-2019 Roy Marples <roy@marples.name>
+ * All rights reserved
+
+ * 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.
+ */
+
+#include <sys/socket.h>
+#include <sys/types.h>
+
+#include <assert.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include "arp.h"
+#include "bpf.h"
+#include "dhcp.h"
+#include "dhcp6.h"
+#include "eloop.h"
+#include "ipv6nd.h"
+#include "logerr.h"
+#include "privsep.h"
+
+#ifdef INET
+static void
+ps_inet_recvbootp(void *arg)
+{
+	struct dhcpcd_ctx *ctx = arg;
+
+	if (ps_recvmsg(ctx, ctx->udp_fd, PS_BOOTP, ctx->ps_inet_fd) == -1)
+		logerr(__func__);
+}
+#endif
+
+#ifdef INET6
+static void
+ps_inet_recvra(void *arg)
+{
+	struct dhcpcd_ctx *ctx = arg;
+
+	if (ps_recvmsg(ctx, ctx->nd_fd, PS_ND, ctx->ps_inet_fd) == -1)
+		logerr(__func__);
+}
+#endif
+
+#ifdef DHCP6
+static void
+ps_inet_recvdhcp6(void *arg)
+{
+	struct dhcpcd_ctx *ctx = arg;
+
+	if (ps_recvmsg(ctx, ctx->dhcp6_fd, PS_DHCP6, ctx->ps_inet_fd) == -1)
+		logerr(__func__);
+}
+#endif
+
+static int
+ps_inet_startcb(void *arg)
+{
+	struct dhcpcd_ctx *ctx = arg;
+	int ret = 0;
+
+	setproctitle("[network proxy]");
+
+	/* This end is the main engine, so it's useless for us. */
+	close(ctx->ps_data_fd);
+	ctx->ps_data_fd = -1;
+
+#ifdef INET
+	if ((ctx->options & (DHCPCD_IPV4 | DHCPCD_MASTER)) ==
+	    (DHCPCD_IPV4 | DHCPCD_MASTER))
+	{
+		ctx->udp_fd = dhcp_openudp(NULL);
+		if (ctx->udp_fd == -1) {
+			logerr("%s: dhcp_open", __func__);
+			return -1;
+		}
+		if (eloop_event_add(ctx->eloop, ctx->udp_fd,
+		    ps_inet_recvbootp, ctx) == -1)
+		{
+			logerr("%s: eloop_event_add DHCP", __func__);
+			return -1;
+		}
+		ret++;
+	}
+#endif
+#if defined(INET6) && !defined(_sun)
+	if (ctx->options & DHCPCD_IPV6) {
+		if (ipv6nd_open(ctx) == -1) {
+			logerr("%s: ipv6nd_open", __func__);
+			return -1;
+		}
+		if (eloop_event_add(ctx->eloop, ctx->nd_fd,
+		    ps_inet_recvra, ctx) == -1)
+		{
+			logerr("%s: eloop_event_add RA", __func__);
+			return -1;
+		}
+		ret++;
+	}
+#endif
+#ifdef DHCP6
+	if ((ctx->options & (DHCPCD_DHCP6 | DHCPCD_MASTER)) ==
+	    (DHCPCD_DHCP6 | DHCPCD_MASTER))
+	{
+		ctx->dhcp6_fd = dhcp6_openudp(0, NULL);
+		if (ctx->dhcp6_fd == -1) {
+			logerr("%s: dhcp6_open", __func__);
+			return -1;
+		}
+		if (eloop_event_add(ctx->eloop, ctx->dhcp6_fd,
+		    ps_inet_recvdhcp6, ctx) == -1)
+		{
+			logerr("%s: eloop_event_add DHCP6", __func__);
+			return -1;
+		}
+		ret++;
+	}
+#endif
+
+	if (ret == 0) {
+		errno = ENXIO;
+		return -1;
+	}
+	return ret;
+}
+
+static ssize_t
+ps_inet_recvmsg_cb(void *arg, struct ps_msghdr *psm, struct msghdr *msg)
+{
+	struct dhcpcd_ctx *ctx = arg;
+	struct ps_process *psp;
+	int s;
+
+	psp = ps_findprocess(ctx, &psm->ps_id);
+	if (psp != NULL) {
+		s = psp->psp_work_fd;
+		logerrx("psp found fd %d", s);
+		goto dosend;
+	}
+
+	switch (psm->ps_cmd) {
+#ifdef INET
+	case PS_BOOTP:
+		s = ctx->udp_fd;
+		break;
+#endif
+#ifdef INET6
+	case PS_ND:
+		s = ctx->nd_fd;
+		break;
+#endif
+#ifdef DHCP6
+	case PS_DHCP6:
+		s = ctx->dhcp6_fd;
+		break;
+#endif
+	default:
+		errno = EINVAL;
+		return -1;
+	}
+
+dosend:
+
+	return sendmsg(s, msg, 0);
+}
+
+/* Receive from state engine, send message on wire. */
+static void
+ps_inet_recvmsg(void *arg)
+{
+	struct dhcpcd_ctx *ctx = arg;
+
+	if (ps_recvpsmsg(ctx, ctx->ps_inet_fd, ps_inet_recvmsg_cb, ctx) == -1)
+		logerr(__func__);
+}
+
+static void
+ps_inet_signalcb(int sig, void *arg)
+{
+	struct dhcpcd_ctx *ctx = arg;
+
+	/* Ignore SIGINT, respect PS_STOP command or SIGTERM. */
+	if (sig == SIGINT)
+		return;
+
+	shutdown(ctx->ps_inet_fd, SHUT_RDWR);
+	eloop_exit(ctx->eloop, sig == SIGTERM ? EXIT_SUCCESS : EXIT_FAILURE);
+}
+
+ssize_t
+ps_inet_dispatch(void *arg, struct ps_msghdr *psm, struct msghdr *msg)
+{
+	struct dhcpcd_ctx *ctx = arg;
+
+	switch (psm->ps_cmd) {
+#ifdef INET
+	case PS_BOOTP:
+		dhcp_recvmsg(ctx, msg);
+		break;
+#endif
+#ifdef INET6
+	case PS_ND:
+		ipv6nd_recvmsg(ctx, msg);
+		break;
+#endif
+#ifdef DHCP6
+	case PS_DHCP6:
+		dhcp6_recvmsg(ctx, msg, NULL);
+		break;
+#endif
+	default:
+		errno = ENOTSUP;
+		return -1;
+	}
+	return 1;
+}
+
+static void
+ps_inet_dodispatch(void *arg)
+{
+	struct dhcpcd_ctx *ctx = arg;
+
+	if (ps_recvpsmsg(ctx, ctx->ps_inet_fd, ps_inet_dispatch, ctx) == -1)
+		logerr(__func__);
+}
+
+pid_t
+ps_inet_start(struct dhcpcd_ctx *ctx)
+{
+
+	return ps_dostart(ctx, &ctx->ps_inet_pid, &ctx->ps_inet_fd,
+	    ps_inet_recvmsg, ps_inet_dodispatch, ctx,
+	    ps_inet_startcb, ps_inet_signalcb, PSF_DROPPRIVS);
+}
+
+int
+ps_inet_stop(struct dhcpcd_ctx *ctx)
+{
+
+	return ps_dostop(ctx, &ctx->ps_inet_pid, &ctx->ps_inet_fd);
+}
+
+ssize_t
+ps_inet_sendmsg(struct dhcpcd_ctx *ctx, uint8_t cmd, struct msghdr *msg)
+{
+
+	return ps_sendmsg(ctx, ctx->ps_inet_fd, cmd, 0, msg);
+}
+
+#ifdef INET
+static void
+ps_inet_recvinbootp(void *arg)
+{
+	struct ps_process *psp = arg;
+
+	if (ps_recvmsg(psp->psp_ctx, psp->psp_work_fd,
+	    PS_BOOTP, psp->psp_ctx->ps_data_fd) == -1)
+		logerr(__func__);
+}
+
+static int
+ps_inet_listenin(void *arg)
+{
+	struct ps_process *psp = arg;
+	struct in_addr *ia = &psp->psp_id.psi_addr.psa_in_addr;
+	char buf[INET_ADDRSTRLEN];
+
+	inet_ntop(AF_INET, ia, buf, sizeof(buf));
+	setproctitle("[network proxy] %s", buf);
+
+	psp->psp_work_fd = dhcp_openudp(ia);
+	if (psp->psp_work_fd == -1) {
+		logerr(__func__);
+		return -1;
+	}
+
+	if (eloop_event_add(psp->psp_ctx->eloop, psp->psp_work_fd,
+	    ps_inet_recvinbootp, psp) == -1)
+	{
+		logerr("%s: eloop_event_add DHCP", __func__);
+		return -1;
+	}
+
+	logdebugx("spawned listener %s on PID %d", buf, getpid());
+	return 0;
+}
+#endif
+
+#ifdef DHCP6
+static void
+ps_inet_recvin6dhcp6(void *arg)
+{
+	struct ps_process *psp = arg;
+
+	if (ps_recvmsg(psp->psp_ctx, psp->psp_work_fd,
+	    PS_DHCP6, psp->psp_ctx->ps_data_fd) == -1)
+		logerr(__func__);
+}
+
+static int
+ps_inet_listenin6(void *arg)
+{
+	struct ps_process *psp = arg;
+	struct in6_addr *ia = &psp->psp_id.psi_addr.psa_in6_addr;
+	char buf[INET6_ADDRSTRLEN];
+
+	inet_ntop(AF_INET6, ia, buf, sizeof(buf));
+	setproctitle("[network proxy] %s", buf);
+
+	psp->psp_work_fd = dhcp6_openudp(psp->psp_id.psi_ifindex, ia);
+	if (psp->psp_work_fd == -1) {
+		logerr(__func__);
+		return -1;
+	}
+
+	if (eloop_event_add(psp->psp_ctx->eloop, psp->psp_work_fd,
+	    ps_inet_recvin6dhcp6, psp) == -1)
+	{
+		logerr("%s: eloop_event_add DHCP", __func__);
+		return -1;
+	}
+
+	logdebugx("spawned listener %s on PID %d", buf, getpid());
+	return 0;
+}
+#endif
+
+static ssize_t
+ps_inet_recvmsgpsp_cb(void *arg, __unused struct ps_msghdr *psm,
+    struct msghdr *msg)
+{
+	struct ps_process *psp = arg;
+
+	return sendmsg(psp->psp_work_fd, msg, 0);
+}
+
+static void
+ps_inet_recvmsgpsp(void *arg)
+{
+	struct ps_process *psp = arg;
+
+	if (ps_recvpsmsg(psp->psp_ctx, psp->psp_fd,
+	    ps_inet_recvmsgpsp_cb, psp) == -1)
+		logerr(__func__);
+}
+
+ssize_t
+ps_inet_cmd(struct dhcpcd_ctx *ctx, struct ps_msghdr *psm,
+    __unused struct msghdr *msg)
+{
+	uint8_t cmd;
+	struct ps_process *psp;
+	int (*start_func)(void *);
+	pid_t start;
+
+	cmd = (uint8_t)(psm->ps_cmd & ~(PS_START | PS_STOP));
+	psp = ps_findprocess(ctx, &psm->ps_id);
+
+#ifdef PRIVSEP_DEBUG
+	logerrx("%s: IN cmd %x, psp %p", __func__, psm->ps_cmd, psp);
+#endif
+
+	if (psm->ps_cmd & PS_STOP) {
+		assert(psp == NULL);
+		return 0;
+	}
+
+	switch (cmd) {
+#ifdef INET
+	case PS_BOOTP:
+		start_func = ps_inet_listenin;
+		break;
+#endif
+#ifdef INET6
+#ifdef __sun
+	case PS_ND:
+		start_func = ps_inet_listennd;
+		break;
+#endif
+#ifdef DHCP6
+	case PS_DHCP6:
+		start_func = ps_inet_listenin6;
+		break;
+#endif
+#endif
+	default:
+		logerrx("%s: unknown command %x", __func__, psm->ps_cmd);
+		errno = ENOTSUP;
+		return -1;
+	}
+
+	if (!(psm->ps_cmd & PS_START)) {
+		errno = EINVAL;
+		return -1;
+	}
+
+	if (psp != NULL)
+		return 1;
+
+	psp = ps_newprocess(ctx, &psm->ps_id);
+	if (psp == NULL)
+		return -1;
+
+	start = ps_dostart(ctx,
+	    &psp->psp_pid, &psp->psp_fd,
+	    ps_inet_recvmsgpsp, NULL, psp,
+	    start_func, ps_inet_signalcb, PSF_DROPPRIVS);
+	switch (start) {
+	case -1:
+		ps_freeprocess(psp);
+		return -1;
+	case 0:
+		break;
+	default:
+		break;
+	}
+	return start;
+}
+
+#ifdef INET
+static ssize_t
+ps_inet_in_docmd(struct ipv4_addr *ia, uint8_t cmd, const struct msghdr *msg)
+{
+	assert(ia != NULL);
+	struct dhcpcd_ctx *ctx = ia->iface->ctx;
+	struct ps_msghdr psm = {
+		.ps_cmd = cmd,
+		.ps_id = {
+			.psi_cmd = (uint8_t)(cmd & ~(PS_START | PS_STOP)),
+			.psi_ifindex = ia->iface->index,
+			.psi_addr.psa_in_addr = ia->addr,
+		},
+	};
+
+	return ps_sendpsmmsg(ctx, ctx->ps_root_fd, &psm, msg);
+}
+
+ssize_t
+ps_inet_openbootp(struct ipv4_addr *ia)
+{
+
+	return ps_inet_in_docmd(ia, PS_START | PS_BOOTP, NULL);
+}
+
+ssize_t
+ps_inet_closebootp(struct ipv4_addr *ia)
+{
+
+	return ps_inet_in_docmd(ia, PS_STOP | PS_BOOTP, NULL);
+}
+
+ssize_t
+ps_inet_sendbootp(struct ipv4_addr *ia, const struct msghdr *msg)
+{
+	struct dhcpcd_ctx *ctx = ia->iface->ctx;
+
+	if (ctx->options & DHCPCD_MASTER)
+		return ps_sendmsg(ctx, ctx->ps_inet_fd, PS_BOOTP, 0, msg);
+	return ps_inet_in_docmd(ia, PS_BOOTP, msg);
+}
+#endif /* INET */
+
+#ifdef INET6
+#ifdef __sun
+static ssize_t
+ps_inet_ifp_docmd(struct interface *ifp, uint8_t cmd, const struct msghdr *msg)
+{
+	struct dhcpcd_ctx *ctx = ia->iface->ctx;
+	struct ps_msghdr psm = {
+		.ps_cmd = cmd,
+		.ps_id = {
+			.psi_cmd = (uint8_t)(cmd & ~(PS_START | PS_STOP)),
+			.psi_ifindex = ifp->index,
+		},
+	};
+
+	return ps_sendpsmmsg(ctx, ctx->ps_root_fd, &psm, msg);
+}
+
+ssize_t
+ps_inet_opennd(struct interface *ifp)
+{
+
+	return ps_inet_ifp_docmd(ifp, PS_ND | PS_START, NULL);
+}
+
+ssize_t
+ps_inet_closend(struct interface *ifp)
+{
+
+	return ps_inet_ifp_docmd(ia, PS_ND | PS_STOP, NULL);
+}
+
+ssize_t
+ps_inet_sendnd(struct interface *ifp, const struct msghdr *msg)
+{
+
+	return ps_inet_ifp_docmd(ifp, PS_ND, msg);
+}
+#endif /* __sun */
+
+#ifdef DHCP6
+static ssize_t
+ps_inet_in6_docmd(struct ipv6_addr *ia, uint8_t cmd, const struct msghdr *msg)
+{
+	struct dhcpcd_ctx *ctx = ia->iface->ctx;
+	struct ps_msghdr psm = {
+		.ps_cmd = cmd,
+		.ps_id = {
+			.psi_cmd = (uint8_t)(cmd & ~(PS_START | PS_STOP)),
+			.psi_ifindex = ia->iface->index,
+			.psi_addr.psa_in6_addr = ia->addr,
+		},
+	};
+
+	return ps_sendpsmmsg(ctx, ctx->ps_root_fd, &psm, msg);
+}
+
+ssize_t
+ps_inet_opendhcp6(struct ipv6_addr *ia)
+{
+
+	return ps_inet_in6_docmd(ia, PS_DHCP6 | PS_START, NULL);
+}
+
+ssize_t
+ps_inet_closedhcp6(struct ipv6_addr *ia)
+{
+
+	return ps_inet_in6_docmd(ia, PS_DHCP6 | PS_STOP, NULL);
+}
+
+ssize_t
+ps_inet_senddhcp6(struct ipv6_addr *ia, const struct msghdr *msg)
+{
+	struct dhcpcd_ctx *ctx = ia->iface->ctx;
+
+	if (ctx->options & DHCPCD_MASTER)
+		return ps_sendmsg(ctx, ctx->ps_inet_fd, PS_DHCP6, 0, msg);
+	return ps_inet_in6_docmd(ia, PS_DHCP6, msg);
+}
+#endif /* DHCP6 */
+#endif /* INET6 */