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ndhc/scriptd.c

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Support running an executable file when a new lease is acquired. If no 'script-file = SCRIPTFILE' is specified in the configuration file and if no '-X SCRIPTFILE' or '--script-file SCRIPTFILE' command argument is provided, then this functionality is entirely inactive and no associated subprocess is spawned. Otherwise, ndhc will spawn a subprocess that runs as root that has the sole job of forking off a subprocess that exec's the specified script in a sanitized and fixed-state environment whenever a new DHCPv4 lease is acquired. Note that this script is provided no information about ndhc or the DHCP state in the environment or in any argument fields; it is the responsibility of this script to gather whatever information it needs from either the filesystem or syscalls. This design is intended to avoid the historical problems that are associated with dhcp clients invoking scripts. The path of the scriptfile cannot be changed after ndhc is initially run; ndhc forks off the privsep script subprocess that executes scripts after it has read the configuration file and command arguments, but before it begins processing network data; thus, it is impossible for the network-handling process to modify or influence the script assuming proper OS memory protection. The privsep channel communicates that the script should be run by simply writing a newline; anything else will result in ndhc terminating itself. Before the recommended way to update system state after a change in lease information was to run the fcactus program and watch the associated leasefile for the interface for modification; now no external program is needed for this job.
2022-02-24 11:22:26 +05:30
// Copyright 2022 Nicholas J. Kain <njkain at gmail dot com>
// SPDX-License-Identifier: MIT
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <assert.h>
#include <poll.h>
#include <signal.h>
#include <sys/wait.h>
#include <sys/prctl.h>
#include <sys/stat.h>
Set FD_CLOEXEC on scriptd(Sock|Stream). These have no reason to be inherited by the script when it is run by posix_spawn().
2022-09-08 02:55:22 +05:30
#include <fcntl.h>
Support running an executable file when a new lease is acquired. If no 'script-file = SCRIPTFILE' is specified in the configuration file and if no '-X SCRIPTFILE' or '--script-file SCRIPTFILE' command argument is provided, then this functionality is entirely inactive and no associated subprocess is spawned. Otherwise, ndhc will spawn a subprocess that runs as root that has the sole job of forking off a subprocess that exec's the specified script in a sanitized and fixed-state environment whenever a new DHCPv4 lease is acquired. Note that this script is provided no information about ndhc or the DHCP state in the environment or in any argument fields; it is the responsibility of this script to gather whatever information it needs from either the filesystem or syscalls. This design is intended to avoid the historical problems that are associated with dhcp clients invoking scripts. The path of the scriptfile cannot be changed after ndhc is initially run; ndhc forks off the privsep script subprocess that executes scripts after it has read the configuration file and command arguments, but before it begins processing network data; thus, it is impossible for the network-handling process to modify or influence the script assuming proper OS memory protection. The privsep channel communicates that the script should be run by simply writing a newline; anything else will result in ndhc terminating itself. Before the recommended way to update system state after a change in lease information was to run the fcactus program and watch the associated leasefile for the interface for modification; now no external program is needed for this job.
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#include "nk/log.h"
#include "nk/io.h"
scriptd: Use posix_spawn rather than fork/exec. Also don't bother providing an artificial environment.
2022-08-09 23:10:10 +05:30
#include "nk/pspawn.h"
Support running an executable file when a new lease is acquired. If no 'script-file = SCRIPTFILE' is specified in the configuration file and if no '-X SCRIPTFILE' or '--script-file SCRIPTFILE' command argument is provided, then this functionality is entirely inactive and no associated subprocess is spawned. Otherwise, ndhc will spawn a subprocess that runs as root that has the sole job of forking off a subprocess that exec's the specified script in a sanitized and fixed-state environment whenever a new DHCPv4 lease is acquired. Note that this script is provided no information about ndhc or the DHCP state in the environment or in any argument fields; it is the responsibility of this script to gather whatever information it needs from either the filesystem or syscalls. This design is intended to avoid the historical problems that are associated with dhcp clients invoking scripts. The path of the scriptfile cannot be changed after ndhc is initially run; ndhc forks off the privsep script subprocess that executes scripts after it has read the configuration file and command arguments, but before it begins processing network data; thus, it is impossible for the network-handling process to modify or influence the script assuming proper OS memory protection. The privsep channel communicates that the script should be run by simply writing a newline; anything else will result in ndhc terminating itself. Before the recommended way to update system state after a change in lease information was to run the fcactus program and watch the associated leasefile for the interface for modification; now no external program is needed for this job.
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#include "scriptd.h"
#include "ndhc.h"
#include "sys.h"
scriptd: Use posix_spawn rather than fork/exec. Also don't bother providing an artificial environment.
2022-08-09 23:10:10 +05:30
extern char **environ;
Support running an executable file when a new lease is acquired. If no 'script-file = SCRIPTFILE' is specified in the configuration file and if no '-X SCRIPTFILE' or '--script-file SCRIPTFILE' command argument is provided, then this functionality is entirely inactive and no associated subprocess is spawned. Otherwise, ndhc will spawn a subprocess that runs as root that has the sole job of forking off a subprocess that exec's the specified script in a sanitized and fixed-state environment whenever a new DHCPv4 lease is acquired. Note that this script is provided no information about ndhc or the DHCP state in the environment or in any argument fields; it is the responsibility of this script to gather whatever information it needs from either the filesystem or syscalls. This design is intended to avoid the historical problems that are associated with dhcp clients invoking scripts. The path of the scriptfile cannot be changed after ndhc is initially run; ndhc forks off the privsep script subprocess that executes scripts after it has read the configuration file and command arguments, but before it begins processing network data; thus, it is impossible for the network-handling process to modify or influence the script assuming proper OS memory protection. The privsep channel communicates that the script should be run by simply writing a newline; anything else will result in ndhc terminating itself. Before the recommended way to update system state after a change in lease information was to run the fcactus program and watch the associated leasefile for the interface for modification; now no external program is needed for this job.
2022-02-24 11:22:26 +05:30
bool valid_script_file = false;
// Runs the 'script_file'-specified script. Called from ndhc process.
scriptd: Wait to notify s6 until script completes. The motivation here is to be safe in cases where the script is setting up firewall rules or tunnels and where subsequent tasks require these to be complete before starting. I expect that this is a common case where a script is used. The implementation behaves almost identically to how ifchd works.
2022-09-07 14:15:30 +05:30
// Blocks until the script finishes running.
Support running an executable file when a new lease is acquired. If no 'script-file = SCRIPTFILE' is specified in the configuration file and if no '-X SCRIPTFILE' or '--script-file SCRIPTFILE' command argument is provided, then this functionality is entirely inactive and no associated subprocess is spawned. Otherwise, ndhc will spawn a subprocess that runs as root that has the sole job of forking off a subprocess that exec's the specified script in a sanitized and fixed-state environment whenever a new DHCPv4 lease is acquired. Note that this script is provided no information about ndhc or the DHCP state in the environment or in any argument fields; it is the responsibility of this script to gather whatever information it needs from either the filesystem or syscalls. This design is intended to avoid the historical problems that are associated with dhcp clients invoking scripts. The path of the scriptfile cannot be changed after ndhc is initially run; ndhc forks off the privsep script subprocess that executes scripts after it has read the configuration file and command arguments, but before it begins processing network data; thus, it is impossible for the network-handling process to modify or influence the script assuming proper OS memory protection. The privsep channel communicates that the script should be run by simply writing a newline; anything else will result in ndhc terminating itself. Before the recommended way to update system state after a change in lease information was to run the fcactus program and watch the associated leasefile for the interface for modification; now no external program is needed for this job.
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void request_scriptd_run(void)
{
if (!valid_script_file) return;
scriptd: Wait to notify s6 until script completes. The motivation here is to be safe in cases where the script is setting up firewall rules or tunnels and where subsequent tasks require these to be complete before starting. I expect that this is a common case where a script is used. The implementation behaves almost identically to how ifchd works.
2022-09-07 14:15:30 +05:30
char nl = '\n';
ssize_t r = safe_write(scriptdSock[0], &nl, 1);
Support running an executable file when a new lease is acquired. If no 'script-file = SCRIPTFILE' is specified in the configuration file and if no '-X SCRIPTFILE' or '--script-file SCRIPTFILE' command argument is provided, then this functionality is entirely inactive and no associated subprocess is spawned. Otherwise, ndhc will spawn a subprocess that runs as root that has the sole job of forking off a subprocess that exec's the specified script in a sanitized and fixed-state environment whenever a new DHCPv4 lease is acquired. Note that this script is provided no information about ndhc or the DHCP state in the environment or in any argument fields; it is the responsibility of this script to gather whatever information it needs from either the filesystem or syscalls. This design is intended to avoid the historical problems that are associated with dhcp clients invoking scripts. The path of the scriptfile cannot be changed after ndhc is initially run; ndhc forks off the privsep script subprocess that executes scripts after it has read the configuration file and command arguments, but before it begins processing network data; thus, it is impossible for the network-handling process to modify or influence the script assuming proper OS memory protection. The privsep channel communicates that the script should be run by simply writing a newline; anything else will result in ndhc terminating itself. Before the recommended way to update system state after a change in lease information was to run the fcactus program and watch the associated leasefile for the interface for modification; now no external program is needed for this job.
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if (r < 0 || (size_t)r != 1)
suicide("%s: (%s) write failed: %zd", client_config.interface,
__func__, r);
scriptd: Wait to notify s6 until script completes. The motivation here is to be safe in cases where the script is setting up firewall rules or tunnels and where subsequent tasks require these to be complete before starting. I expect that this is a common case where a script is used. The implementation behaves almost identically to how ifchd works.
2022-09-07 14:15:30 +05:30
char buf[16];
Correct regression introduced by previous commit. safe_recv(..., len), when used on a blocking fd, will attempt to call recv and collect data until either EOF, a hard error, or len bytes are collected. The previous commit used safe_recv() in a blocking mode to read a single byte into a buffer that was larger than a byte. This would cause ndhc to stall as safe_recv() would try to fill that buffer when no more data would ever be sent. This issue would only happen if ndhc is supposed to run a script. Introduce and use safe_recv_once() that will correct this problem and fill the semantic gap for blocking fds. I add a new call because in some cases the above behavior might be required for a blocking fd, too. Note that the above issue is not a problem for nonblocking fds; the EAGAIN or EWOULDBLOCK path will return a short read.
2022-09-08 02:38:43 +05:30
r = safe_recv_once(scriptdSock[0], buf, sizeof buf, 0);
scriptd: Wait to notify s6 until script completes. The motivation here is to be safe in cases where the script is setting up firewall rules or tunnels and where subsequent tasks require these to be complete before starting. I expect that this is a common case where a script is used. The implementation behaves almost identically to how ifchd works.
2022-09-07 14:15:30 +05:30
if (r == 0) {
// Remote end hung up.
exit(EXIT_SUCCESS);
} else if (r < 0) {
suicide("%s: (%s) recvmsg failed: %s", client_config.interface,
__func__, strerror(errno));
}
if (r != 1 || buf[0] != '+')
suicide("%s: Bad response from recv", __func__);
Support running an executable file when a new lease is acquired. If no 'script-file = SCRIPTFILE' is specified in the configuration file and if no '-X SCRIPTFILE' or '--script-file SCRIPTFILE' command argument is provided, then this functionality is entirely inactive and no associated subprocess is spawned. Otherwise, ndhc will spawn a subprocess that runs as root that has the sole job of forking off a subprocess that exec's the specified script in a sanitized and fixed-state environment whenever a new DHCPv4 lease is acquired. Note that this script is provided no information about ndhc or the DHCP state in the environment or in any argument fields; it is the responsibility of this script to gather whatever information it needs from either the filesystem or syscalls. This design is intended to avoid the historical problems that are associated with dhcp clients invoking scripts. The path of the scriptfile cannot be changed after ndhc is initially run; ndhc forks off the privsep script subprocess that executes scripts after it has read the configuration file and command arguments, but before it begins processing network data; thus, it is impossible for the network-handling process to modify or influence the script assuming proper OS memory protection. The privsep channel communicates that the script should be run by simply writing a newline; anything else will result in ndhc terminating itself. Before the recommended way to update system state after a change in lease information was to run the fcactus program and watch the associated leasefile for the interface for modification; now no external program is needed for this job.
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}
static void process_client_socket(void)
{
static char buf[32];
static size_t buflen;
if (buflen == sizeof buf)
suicide("%s: (%s) receive buffer exhausted", client_config.interface,
__func__);
int r = safe_recv(scriptdSock[1], buf + buflen, sizeof buf - buflen,
MSG_DONTWAIT);
if (r == 0) {
// Remote end hung up.
exit(EXIT_SUCCESS);
} else if (r < 0) {
if (errno == EAGAIN || errno == EWOULDBLOCK)
return;
suicide("%s: (%s) error reading from ndhc -> scriptd socket: %s",
client_config.interface, __func__, strerror(errno));
}
buflen += (size_t)r;
if (buflen > 1 || buf[0] != '\n') exit(EXIT_SUCCESS);
buflen = 0;
scriptd: Wait to notify s6 until script completes. The motivation here is to be safe in cases where the script is setting up firewall rules or tunnels and where subsequent tasks require these to be complete before starting. I expect that this is a common case where a script is used. The implementation behaves almost identically to how ifchd works.
2022-09-07 14:15:30 +05:30
pid_t pid;
int ret = nk_pspawn(&pid, script_file, NULL, NULL, NULL, environ);
if (ret) log_line("posix_spawn failed for '%s': %s\n", script_file, strerror(ret));
int wstatus;
ret = waitpid(pid, &wstatus, 0);
if (ret == -1)
suicide("%s: (%s) waitpid failed: %s", client_config.interface,
__func__, strerror(errno));
char c = '+';
ssize_t rs = safe_write(scriptdSock[1], &c, 1);
if (rs == 0) {
// Remote end hung up.
exit(EXIT_SUCCESS);
} else if (rs < 0)
suicide("%s: (%s) error writing to scriptd -> ndhc socket: %s",
client_config.interface, __func__, strerror(errno));
Support running an executable file when a new lease is acquired. If no 'script-file = SCRIPTFILE' is specified in the configuration file and if no '-X SCRIPTFILE' or '--script-file SCRIPTFILE' command argument is provided, then this functionality is entirely inactive and no associated subprocess is spawned. Otherwise, ndhc will spawn a subprocess that runs as root that has the sole job of forking off a subprocess that exec's the specified script in a sanitized and fixed-state environment whenever a new DHCPv4 lease is acquired. Note that this script is provided no information about ndhc or the DHCP state in the environment or in any argument fields; it is the responsibility of this script to gather whatever information it needs from either the filesystem or syscalls. This design is intended to avoid the historical problems that are associated with dhcp clients invoking scripts. The path of the scriptfile cannot be changed after ndhc is initially run; ndhc forks off the privsep script subprocess that executes scripts after it has read the configuration file and command arguments, but before it begins processing network data; thus, it is impossible for the network-handling process to modify or influence the script assuming proper OS memory protection. The privsep channel communicates that the script should be run by simply writing a newline; anything else will result in ndhc terminating itself. Before the recommended way to update system state after a change in lease information was to run the fcactus program and watch the associated leasefile for the interface for modification; now no external program is needed for this job.
2022-02-24 11:22:26 +05:30
}
static void do_scriptd_work(void)
{
struct pollfd pfds[2] = {0};
pfds[0].fd = scriptdSock[1];
pfds[0].events = POLLIN|POLLHUP|POLLERR|POLLRDHUP;
pfds[1].fd = scriptdStream[1];
pfds[1].events = POLLHUP|POLLERR|POLLRDHUP;
for (;;) {
if (poll(pfds, 2, -1) < 0) {
if (errno != EINTR) suicide("poll failed");
}
if (pfds[0].revents & POLLIN) {
process_client_socket();
}
if (pfds[0].revents & (POLLHUP|POLLERR|POLLRDHUP)) {
suicide("scriptdSock closed unexpectedly");
}
if (pfds[1].revents & (POLLHUP|POLLERR|POLLRDHUP)) {
exit(EXIT_SUCCESS);
}
}
}
static void signal_handler(int signo)
{
Preserve errno across signals.
2022-02-24 15:36:12 +05:30
int serrno = errno;
scriptd: Wait to notify s6 until script completes. The motivation here is to be safe in cases where the script is setting up firewall rules or tunnels and where subsequent tasks require these to be complete before starting. I expect that this is a common case where a script is used. The implementation behaves almost identically to how ifchd works.
2022-09-07 14:15:30 +05:30
if (signo == SIGINT || signo == SIGTERM) {
Preserve errno across signals.
2022-02-24 15:36:12 +05:30
_exit(EXIT_FAILURE);
Support running an executable file when a new lease is acquired. If no 'script-file = SCRIPTFILE' is specified in the configuration file and if no '-X SCRIPTFILE' or '--script-file SCRIPTFILE' command argument is provided, then this functionality is entirely inactive and no associated subprocess is spawned. Otherwise, ndhc will spawn a subprocess that runs as root that has the sole job of forking off a subprocess that exec's the specified script in a sanitized and fixed-state environment whenever a new DHCPv4 lease is acquired. Note that this script is provided no information about ndhc or the DHCP state in the environment or in any argument fields; it is the responsibility of this script to gather whatever information it needs from either the filesystem or syscalls. This design is intended to avoid the historical problems that are associated with dhcp clients invoking scripts. The path of the scriptfile cannot be changed after ndhc is initially run; ndhc forks off the privsep script subprocess that executes scripts after it has read the configuration file and command arguments, but before it begins processing network data; thus, it is impossible for the network-handling process to modify or influence the script assuming proper OS memory protection. The privsep channel communicates that the script should be run by simply writing a newline; anything else will result in ndhc terminating itself. Before the recommended way to update system state after a change in lease information was to run the fcactus program and watch the associated leasefile for the interface for modification; now no external program is needed for this job.
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}
Preserve errno across signals.
2022-02-24 15:36:12 +05:30
errno = serrno;
Support running an executable file when a new lease is acquired. If no 'script-file = SCRIPTFILE' is specified in the configuration file and if no '-X SCRIPTFILE' or '--script-file SCRIPTFILE' command argument is provided, then this functionality is entirely inactive and no associated subprocess is spawned. Otherwise, ndhc will spawn a subprocess that runs as root that has the sole job of forking off a subprocess that exec's the specified script in a sanitized and fixed-state environment whenever a new DHCPv4 lease is acquired. Note that this script is provided no information about ndhc or the DHCP state in the environment or in any argument fields; it is the responsibility of this script to gather whatever information it needs from either the filesystem or syscalls. This design is intended to avoid the historical problems that are associated with dhcp clients invoking scripts. The path of the scriptfile cannot be changed after ndhc is initially run; ndhc forks off the privsep script subprocess that executes scripts after it has read the configuration file and command arguments, but before it begins processing network data; thus, it is impossible for the network-handling process to modify or influence the script assuming proper OS memory protection. The privsep channel communicates that the script should be run by simply writing a newline; anything else will result in ndhc terminating itself. Before the recommended way to update system state after a change in lease information was to run the fcactus program and watch the associated leasefile for the interface for modification; now no external program is needed for this job.
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}
static void setup_signals_scriptd(void)
{
static const int ss[] = {
scriptd: Wait to notify s6 until script completes. The motivation here is to be safe in cases where the script is setting up firewall rules or tunnels and where subsequent tasks require these to be complete before starting. I expect that this is a common case where a script is used. The implementation behaves almost identically to how ifchd works.
2022-09-07 14:15:30 +05:30
SIGINT, SIGTERM, SIGKILL
Support running an executable file when a new lease is acquired. If no 'script-file = SCRIPTFILE' is specified in the configuration file and if no '-X SCRIPTFILE' or '--script-file SCRIPTFILE' command argument is provided, then this functionality is entirely inactive and no associated subprocess is spawned. Otherwise, ndhc will spawn a subprocess that runs as root that has the sole job of forking off a subprocess that exec's the specified script in a sanitized and fixed-state environment whenever a new DHCPv4 lease is acquired. Note that this script is provided no information about ndhc or the DHCP state in the environment or in any argument fields; it is the responsibility of this script to gather whatever information it needs from either the filesystem or syscalls. This design is intended to avoid the historical problems that are associated with dhcp clients invoking scripts. The path of the scriptfile cannot be changed after ndhc is initially run; ndhc forks off the privsep script subprocess that executes scripts after it has read the configuration file and command arguments, but before it begins processing network data; thus, it is impossible for the network-handling process to modify or influence the script assuming proper OS memory protection. The privsep channel communicates that the script should be run by simply writing a newline; anything else will result in ndhc terminating itself. Before the recommended way to update system state after a change in lease information was to run the fcactus program and watch the associated leasefile for the interface for modification; now no external program is needed for this job.
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};
sigset_t mask;
if (sigprocmask(0, 0, &mask) < 0)
suicide("sigprocmask failed");
for (int i = 0; ss[i] != SIGKILL; ++i)
if (sigdelset(&mask, ss[i]))
suicide("sigdelset failed");
if (sigaddset(&mask, SIGPIPE))
suicide("sigaddset failed");
if (sigprocmask(SIG_SETMASK, &mask, (sigset_t *)0) < 0)
suicide("sigprocmask failed");
struct sigaction sa = {
.sa_handler = signal_handler,
scriptd: Signal handlers don't need SA_NOCLDWAIT set.
2022-09-08 16:47:11 +05:30
.sa_flags = SA_RESTART,
Support running an executable file when a new lease is acquired. If no 'script-file = SCRIPTFILE' is specified in the configuration file and if no '-X SCRIPTFILE' or '--script-file SCRIPTFILE' command argument is provided, then this functionality is entirely inactive and no associated subprocess is spawned. Otherwise, ndhc will spawn a subprocess that runs as root that has the sole job of forking off a subprocess that exec's the specified script in a sanitized and fixed-state environment whenever a new DHCPv4 lease is acquired. Note that this script is provided no information about ndhc or the DHCP state in the environment or in any argument fields; it is the responsibility of this script to gather whatever information it needs from either the filesystem or syscalls. This design is intended to avoid the historical problems that are associated with dhcp clients invoking scripts. The path of the scriptfile cannot be changed after ndhc is initially run; ndhc forks off the privsep script subprocess that executes scripts after it has read the configuration file and command arguments, but before it begins processing network data; thus, it is impossible for the network-handling process to modify or influence the script assuming proper OS memory protection. The privsep channel communicates that the script should be run by simply writing a newline; anything else will result in ndhc terminating itself. Before the recommended way to update system state after a change in lease information was to run the fcactus program and watch the associated leasefile for the interface for modification; now no external program is needed for this job.
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};
if (sigemptyset(&sa.sa_mask))
suicide("sigemptyset failed");
for (int i = 0; ss[i] != SIGKILL; ++i)
if (sigaction(ss[i], &sa, NULL))
suicide("sigaction failed");
}
void scriptd_main(void)
{
assert(valid_script_file);
prctl(PR_SET_NAME, "ndhc: scriptd");
umask(077);
setup_signals_scriptd();
Set FD_CLOEXEC on scriptd(Sock|Stream). These have no reason to be inherited by the script when it is run by posix_spawn().
2022-09-08 02:55:22 +05:30
fcntl(scriptdSock[1], F_SETFD, FD_CLOEXEC);
fcntl(scriptdStream[1], F_SETFD, FD_CLOEXEC);
Support running an executable file when a new lease is acquired. If no 'script-file = SCRIPTFILE' is specified in the configuration file and if no '-X SCRIPTFILE' or '--script-file SCRIPTFILE' command argument is provided, then this functionality is entirely inactive and no associated subprocess is spawned. Otherwise, ndhc will spawn a subprocess that runs as root that has the sole job of forking off a subprocess that exec's the specified script in a sanitized and fixed-state environment whenever a new DHCPv4 lease is acquired. Note that this script is provided no information about ndhc or the DHCP state in the environment or in any argument fields; it is the responsibility of this script to gather whatever information it needs from either the filesystem or syscalls. This design is intended to avoid the historical problems that are associated with dhcp clients invoking scripts. The path of the scriptfile cannot be changed after ndhc is initially run; ndhc forks off the privsep script subprocess that executes scripts after it has read the configuration file and command arguments, but before it begins processing network data; thus, it is impossible for the network-handling process to modify or influence the script assuming proper OS memory protection. The privsep channel communicates that the script should be run by simply writing a newline; anything else will result in ndhc terminating itself. Before the recommended way to update system state after a change in lease information was to run the fcactus program and watch the associated leasefile for the interface for modification; now no external program is needed for this job.
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do_scriptd_work();
}