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, 108 insertions, 0 deletions

diff --git a/src/privsep-bsd.c b/src/privsep-bsd.c
new file mode 100644
index 00000000..76085dd4
--- /dev/null
+++ b/src/privsep-bsd.c
@@ -0,0 +1,108 @@
+/* SPDX-License-Identifier: BSD-2-Clause */
+/*
+ * Priviledge Separation for dhcpcd, BSD driver
+ * 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/ioctl.h>
+
+#include <errno.h>
+#include <unistd.h>
+
+#include "dhcpcd.h"
+#include "logerr.h"
+#include "privsep.h"
+
+static ssize_t
+ps_root_doioctl6(unsigned long req, void *data, size_t len)
+{
+	int s, err;
+
+	s = socket(PF_INET6, SOCK_DGRAM, 0);
+	if (s != -1)
+		err = ioctl(s, req, data, len);
+	else
+		err = -1;
+	if (err == -1)
+		logerr(__func__);
+	if (s != -1)
+		close(s);
+	return err;
+}
+
+static ssize_t
+ps_root_doroute(void *data, size_t len)
+{
+	int s;
+	ssize_t err;
+
+	s = socket(PF_ROUTE, SOCK_RAW, 0);
+	if (s != -1)
+		err = write(s, data, len);
+	else
+		err = -1;
+	if (err == -1)
+		logerr(__func__);
+	if (s != -1)
+		close(s);
+	return err;
+}
+
+ssize_t
+ps_root_os(struct ps_msghdr *psm, struct msghdr *msg)
+{
+	struct iovec *iov = msg->msg_iov;
+	void *data = iov->iov_base;
+	size_t len = iov->iov_len;
+
+	switch (psm->ps_cmd) {
+	case PS_IOCTL6:
+		return ps_root_doioctl6(psm->ps_flags, data, len);
+	case PS_ROUTE:
+		return ps_root_doroute(data, len);
+	default:
+		errno = ENOTSUP;
+		return -1;
+	}
+}
+
+ssize_t
+ps_root_ioctl6(struct dhcpcd_ctx *ctx, unsigned long request, void *data, size_t len)
+{
+
+	if (ps_sendcmd(ctx, ctx->ps_root_fd, PS_IOCTL6,
+	    request, data, len) == -1)
+		return -1;
+	return ps_root_readerror(ctx);
+}
+
+ssize_t
+ps_root_route(struct dhcpcd_ctx *ctx, void *data, size_t len)
+{
+
+	if (ps_sendcmd(ctx, ctx->ps_root_fd, PS_ROUTE, 0, data, len) == -1)
+		return -1;
+	return ps_root_readerror(ctx);
+}