From 41e91ccdf9fa3097d7b90718cc83e743f4dc8d6b Mon Sep 17 00:00:00 2001

From: Jan Rybar <jrybar@redhat.com>

Date: Thu, 17 Aug 2017 18:01:42 +0200

Subject: [PATCH] nspawn: new option to start as PID2

Cherry-picked from: 7732f92

Resolves: #1417387

---

 Makefile.am                   |   2 +

 man/systemd-nspawn.xml        |  65 +++++++++--

 src/nspawn/nspawn-stub-pid1.c | 196 ++++++++++++++++++++++++++++++++++

 src/nspawn/nspawn-stub-pid1.h |  22 ++++

 src/nspawn/nspawn.c           |  56 ++++++++--

 5 files changed, 328 insertions(+), 13 deletions(-)

 create mode 100644 src/nspawn/nspawn-stub-pid1.c

 create mode 100644 src/nspawn/nspawn-stub-pid1.h

diff --git a/Makefile.am b/Makefile.am

index 7c58fd0504..0e2f8d561c 100644

--- a/Makefile.am

+++ b/Makefile.am

@@ -2658,6 +2658,8 @@ systemd_cgtop_LDADD = \

 # ------------------------------------------------------------------------------

 systemd_nspawn_SOURCES = \

 	src/nspawn/nspawn.c \

+	src/nspawn/nspawn-stub-pid1.c \

+	src/nspawn/nspawn-stub-pid1.h \

 	src/core/mount-setup.c \

 	src/core/mount-setup.h \

 	src/core/loopback-setup.c \

diff --git a/man/systemd-nspawn.xml b/man/systemd-nspawn.xml

index cbd44d4aba..d0eddaacc3 100644

--- a/man/systemd-nspawn.xml

+++ b/man/systemd-nspawn.xml

@@ -241,16 +241,69 @@

         <option>--ephemeral</option>.</para></listitem>

       </varlistentry>

+      <varlistentry>

+      <term><option>-a</option></term>

+        <term><option>--as-pid2</option></term>

+

+        <listitem><para>Invoke the shell or specified program as process ID (PID) 2 instead of PID 1 (init). By

+        default, if neither this option nor <option>--boot</option> is used, the selected binary is run as process with

+        PID 1, a mode only suitable for programs that are aware of the special semantics that the process with PID 1

+        has on UNIX. For example, it needs to reap all processes reparented to it, and should implement

+        <command>sysvinit</command> compatible signal handling (specifically: it needs to reboot on SIGINT, reexecute

+        on SIGTERM, reload configuration on SIGHUP, and so on). With <option>--as-pid2</option> a minimal stub init

+        process is run as PID 1 and the selected binary is executed as PID 2 (and hence does not need to implement any

+        special semantics). The stub init process will reap processes as necessary and react appropriately to

+        signals. It is recommended to use this mode to invoke arbitrary commands in containers, unless they have been

+        modified to run correctly as PID 1. Or in other words: this switch should be used for pretty much all commands,

+        except when the command refers to an init or shell implementation, as these are generally capable of running

+        correctly as PID 1). This option may not be combined with <option>--boot</option> or

+        <option>--share-system</option>.</para>

+        </listitem>

+      </varlistentry>

+

       <varlistentry>

         <term><option>-b</option></term>

         <term><option>--boot</option></term>

-        <listitem><para>Automatically search for an init binary and

-        invoke it instead of a shell or a user supplied program. If

-        this option is used, arguments specified on the command line

-        are used as arguments for the init binary. This option may not

-        be combined with <option>--share-system</option>.

-        </para></listitem>

+        <listitem><para>Automatically search for an init binary and invoke it as PID 1, instead of a shell or a user

+        supplied program. If this option is used, arguments specified on the command line are used as arguments for the

+        init binary. This option may not be combined with <option>--as-pid2</option> or

+        <option>--share-system</option>.</para>

+

+        <para>The following table explains the different modes of invocation and relationship to

+        <option>--as-pid2</option> (see above):</para>

+

+        

+          <title>Invocation Mode</title>

+          <tgroup cols='2' align='left' colsep='1' rowsep='1'>

+            <colspec colname="switch" />

+            <colspec colname="explanation" />

+            

+              <row>

+                <entry>Switch</entry>

+                <entry>Explanation</entry>

+              </row>

+            

+            

+              <row>

+                <entry>Neither <option>--as-pid2</option> nor <option>--boot</option> specified</entry>

+                <entry>The passed parameters are interpreted as command line, which is executed as PID 1 in the container.</entry>

+              </row>

+

+              <row>

+                <entry><option>--as-pid2</option> specified</entry>

+                <entry>The passed parameters are interpreted as command line, which are executed as PID 2 in the container. A stub init process is run as PID 1.</entry>

+              </row>

+

+              <row>

+                <entry><option>--boot</option> specified</entry>

+                <entry>An init binary as automatically searched and run as PID 1 in the container. The passed parameters are used as invocation parameters for this process.</entry>

+              </row>

+

+            

+          </tgroup>

+        

+        </listitem>

       </varlistentry>

       <varlistentry>

diff --git a/src/nspawn/nspawn-stub-pid1.c b/src/nspawn/nspawn-stub-pid1.c

new file mode 100644

index 0000000000..11c11560c4

--- /dev/null

+++ b/src/nspawn/nspawn-stub-pid1.c

@@ -0,0 +1,196 @@

+/***

+  This file is part of systemd.

+

+  Copyright 2016 Lennart Poettering

+

+  systemd is free software; you can redistribute it and/or modify it

+  under the terms of the GNU Lesser General Public License as published by

+  the Free Software Foundation; either version 2.1 of the License, or

+  (at your option) any later version.

+

+  systemd is distributed in the hope that it will be useful, but

+  WITHOUT ANY WARRANTY; without even the implied warranty of

+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU

+  Lesser General Public License for more details.

+

+  You should have received a copy of the GNU Lesser General Public License

+  along with systemd; If not, see <http://www.gnu.org/licenses/>.

+***/

+

+#include <sys/reboot.h>

+#include <sys/unistd.h>

+#include <sys/wait.h>

+#include <sys/prctl.h>

+

+#include "log.h"

+#include "nspawn-stub-pid1.h"

+#include "util.h"

+#include "time-util.h"

+#include "def.h"

+

+static int reset_environ(const char *new_environment, size_t length) {

+        unsigned long start, end;

+

+        start = (unsigned long) new_environment;

+        end = start + length;

+

+        if (prctl(PR_SET_MM, PR_SET_MM_ENV_START, start, 0, 0) < 0)

+                return -errno;

+

+        if (prctl(PR_SET_MM, PR_SET_MM_ENV_END, end, 0, 0) < 0)

+                return -errno;

+

+        return 0;

+}

+

+int stub_pid1(sd_id128_t uuid) {

+        enum {

+                STATE_RUNNING,

+                STATE_REBOOT,

+                STATE_POWEROFF,

+        } state = STATE_RUNNING;

+

+        sigset_t fullmask, oldmask, waitmask;

+        usec_t quit_usec = USEC_INFINITY;

+        pid_t pid;

+        int r;

+

+        /* The new environment we set up, on the stack. */

+        char new_environment[] =

+                "container=systemd-nspawn\0"

+                "container_uuid=XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX";

+

+        /* Implements a stub PID 1, that reaps all processes and processes a couple of standard signals. This is useful

+         * for allowing arbitrary processes run in a container, and still have all zombies reaped. */

+

+        assert_se(sigfillset(&fullmask) >= 0);

+        assert_se(sigprocmask(SIG_BLOCK, &fullmask, &oldmask) >= 0);

+

+        pid = fork();

+        if (pid < 0)

+                return log_error_errno(errno, "Failed to fork child pid: %m");

+

+        if (pid == 0) {

+                /* Return in the child */

+                assert_se(sigprocmask(SIG_SETMASK, &oldmask, NULL) >= 0);

+                setsid();

+                return 0;

+        }

+

+        reset_all_signal_handlers();

+

+        log_close();

+        close_all_fds(NULL, 0);

+        log_open();

+

+        /* Flush out /proc/self/environ, so that we don't leak the environment from the host into the container. Also,

+         * set $container= and $container_uuid= so that clients in the container that query it from /proc/1/environ

+         * find them set. */

+        sd_id128_to_string(uuid, new_environment + sizeof(new_environment) - SD_ID128_STRING_MAX);

+        reset_environ(new_environment, sizeof(new_environment));

+

+        rename_process("STUBINIT");

+

+        assert_se(sigemptyset(&waitmask) >= 0);

+

+        sigset_add_many(&waitmask,

+                        SIGCHLD,          /* posix: process died */

+                        SIGINT,           /* sysv: ctrl-alt-del */

+                        SIGRTMIN+3,       /* systemd: halt */

+                        SIGRTMIN+4,       /* systemd: poweroff */

+                        SIGRTMIN+5,       /* systemd: reboot */

+                        SIGRTMIN+6,       /* systemd: kexec */

+                        SIGRTMIN+13,      /* systemd: halt */

+                        SIGRTMIN+14,      /* systemd: poweroff */

+                        SIGRTMIN+15,      /* systemd: reboot */

+                        SIGRTMIN+16,      /* systemd: kexec */

+                        -1);

+

+        /* Note that we ignore SIGTERM (sysv's reexec), SIGHUP (reload), and all other signals here, since we don't

+         * support reexec/reloading in this stub process. */

+

+        for (;;) {

+                siginfo_t si;

+                usec_t current_usec;

+

+                si.si_pid = 0;

+                r = waitid(P_ALL, 0, &si, WEXITED|WNOHANG);

+                if (r < 0) {

+                        r = log_error_errno(errno, "Failed to reap children: %m");

+                        goto finish;

+                }

+

+                current_usec = now(CLOCK_MONOTONIC);

+

+                if (si.si_pid == pid || current_usec >= quit_usec) {

+

+                        /* The child we started ourselves died or we reached a timeout. */

+

+                        if (state == STATE_REBOOT) { /* dispatch a queued reboot */

+                                (void) reboot(RB_AUTOBOOT);

+                                r = log_error_errno(errno, "Failed to reboot: %m");

+                                goto finish;

+

+                        } else if (state == STATE_POWEROFF)

+                                (void) reboot(RB_POWER_OFF); /* if this fails, fall back to normal exit. */

+

+                        if (si.si_pid == pid && si.si_code == CLD_EXITED)

+                                r = si.si_status; /* pass on exit code */

+                        else

+                                r = 255; /* signal, coredump, timeout, … */

+

+                        goto finish;

+                }

+                if (si.si_pid != 0)

+                        /* We reaped something. Retry until there's nothing more to reap. */

+                        continue;

+

+                if (quit_usec == USEC_INFINITY)

+                        r = sigwaitinfo(&waitmask, &si);

+                else {

+                        struct timespec ts;

+                        r = sigtimedwait(&waitmask, &si, timespec_store(&ts, quit_usec - current_usec));

+                }

+                if (r < 0) {

+                        if (errno == EINTR) /* strace -p attach can result in EINTR, let's handle this nicely. */

+                                continue;

+                        if (errno == EAGAIN) /* timeout reached */

+                                continue;

+

+                        r = log_error_errno(errno, "Failed to wait for signal: %m");

+                        goto finish;

+                }

+

+                if (si.si_signo == SIGCHLD)

+                        continue; /* Let's reap this */

+

+                if (state != STATE_RUNNING)

+                        continue;

+

+                /* Would love to use a switch() statement here, but SIGRTMIN is actually a function call, not a

+                 * constant… */

+

+                if (si.si_signo == SIGRTMIN+3 ||

+                    si.si_signo == SIGRTMIN+4 ||

+                    si.si_signo == SIGRTMIN+13 ||

+                    si.si_signo == SIGRTMIN+14)

+

+                        state = STATE_POWEROFF;

+

+                else if (si.si_signo == SIGINT ||

+                         si.si_signo == SIGRTMIN+5 ||

+                         si.si_signo == SIGRTMIN+6 ||

+                         si.si_signo == SIGRTMIN+15 ||

+                         si.si_signo == SIGRTMIN+16)

+

+                        state = STATE_REBOOT;

+                else

+                        assert_not_reached("Got unexpected signal");

+

+                /* (void) kill_and_sigcont(pid, SIGTERM); */

+                quit_usec = now(CLOCK_MONOTONIC) + DEFAULT_TIMEOUT_USEC;

+        }

+

+finish:

+        _exit(r < 0 ? EXIT_FAILURE : r);

+}

diff --git a/src/nspawn/nspawn-stub-pid1.h b/src/nspawn/nspawn-stub-pid1.h

new file mode 100644

index 0000000000..be0f1af4cb

--- /dev/null

+++ b/src/nspawn/nspawn-stub-pid1.h

@@ -0,0 +1,22 @@

+#pragma once

+

+/***

+  This file is part of systemd.

+

+  Copyright 2016 Lennart Poettering

+

+  systemd is free software; you can redistribute it and/or modify it

+  under the terms of the GNU Lesser General Public License as published by

+  the Free Software Foundation; either version 2.1 of the License, or

+  (at your option) any later version.

+

+  systemd is distributed in the hope that it will be useful, but

+  WITHOUT ANY WARRANTY; without even the implied warranty of

+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU

+  Lesser General Public License for more details.

+

+  You should have received a copy of the GNU Lesser General Public License

+  along with systemd; If not, see <http://www.gnu.org/licenses/>.

+***/

+

+int stub_pid1(sd_id128_t uuid);

diff --git a/src/nspawn/nspawn.c b/src/nspawn/nspawn.c

index d0003d3790..ea365b3f9b 100644

--- a/src/nspawn/nspawn.c

+++ b/src/nspawn/nspawn.c

@@ -99,6 +99,7 @@

 #include "in-addr-util.h"

 #include "fw-util.h"

 #include "local-addresses.h"

+#include "nspawn-stub-pid1.h"

 #ifdef HAVE_SECCOMP

 #include "seccomp-util.h"

@@ -129,6 +130,14 @@ typedef enum Volatile {

         VOLATILE_STATE,

 } Volatile;

+typedef enum StartMode {

+        START_PID1, /* Run parameters as command line as process 1 */

+        START_PID2, /* Use stub init process as PID 1, run parameters as command line as process 2 */

+        START_BOOT, /* Search for init system, pass arguments as parameters */

+        _START_MODE_MAX,

+        _START_MODE_INVALID = -1

+} StartMode;

+

 static char *arg_directory = NULL;

 static char *arg_template = NULL;

 static char *arg_user = NULL;

@@ -139,7 +148,7 @@ static const char *arg_selinux_apifs_context = NULL;

 static const char *arg_slice = NULL;

 static bool arg_private_network = false;

 static bool arg_read_only = false;

-static bool arg_boot = false;

+static StartMode arg_start_mode = START_PID1;

 static bool arg_ephemeral = false;

 static LinkJournal arg_link_journal = LINK_AUTO;

 static bool arg_link_journal_try = false;

@@ -200,6 +209,7 @@ static void help(void) {

                "  -x --ephemeral            Run container with snapshot of root directory, and\n"

                "                            remove it after exit\n"

                "  -i --image=PATH           File system device or disk image for the container\n"

+               "  -a --as-pid2              Maintain a stub init as PID1, invoke binary as PID2\n"

                "  -b --boot                 Boot up full system (i.e. invoke init)\n"

                "  -u --user=USER            Run the command under specified user or uid\n"

                "  -M --machine=NAME         Set the machine name for the container\n"

@@ -304,6 +314,7 @@ static int parse_argv(int argc, char *argv[]) {

                 { "ephemeral",             no_argument,       NULL, 'x'                   },

                 { "user",                  required_argument, NULL, 'u'                   },

                 { "private-network",       no_argument,       NULL, ARG_PRIVATE_NETWORK   },

+                { "as-pid2",               no_argument,       NULL, 'a'                   },

                 { "boot",                  no_argument,       NULL, 'b'                   },

                 { "uuid",                  required_argument, NULL, ARG_UUID              },

                 { "read-only",             no_argument,       NULL, ARG_READ_ONLY         },

@@ -340,7 +351,7 @@ static int parse_argv(int argc, char *argv[]) {

         assert(argc >= 0);

         assert(argv);

-        while ((c = getopt_long(argc, argv, "+hD:u:bL:M:jS:Z:qi:xp:n", options, NULL)) >= 0)

+        while ((c = getopt_long(argc, argv, "+hD:u:abL:M:jS:Z:qi:xp:n", options, NULL)) >= 0)

                 switch (c) {

@@ -421,7 +432,21 @@ static int parse_argv(int argc, char *argv[]) {

                         break;

                 case 'b':

-                        arg_boot = true;

+                        if (arg_start_mode == START_PID2) {

+                                log_error("--boot and --as-pid2 may not be combined.");

+                                return -EINVAL;

+                        }

+

+                        arg_start_mode = START_BOOT;

+                        break;

+

+                case 'a':

+                        if (arg_start_mode == START_BOOT) {

+                                log_error("--boot and --as-pid2 may not be combined.");

+                                return -EINVAL;

+                        }

+

+                        arg_start_mode = START_PID2;

                         break;

                 case ARG_UUID:

@@ -741,7 +766,7 @@ static int parse_argv(int argc, char *argv[]) {

         if (arg_share_system)

                 arg_register = false;

-        if (arg_boot && arg_share_system) {

+        if (arg_start_mode != START_PID1 && arg_share_system) {

                 log_error("--boot and --share-system may not be combined.");

                 return -EINVAL;

         }

@@ -3586,6 +3611,10 @@ int main(int argc, char *argv[]) {

         log_parse_environment();

         log_open();

+        /* Make sure rename_process() in the stub init process can work */

+        saved_argv = argv;

+        saved_argc = argc;

+

         r = parse_argv(argc, argv);

         if (r <= 0)

                 goto finish;

@@ -3694,7 +3723,7 @@ int main(int argc, char *argv[]) {

                         }

                 }

-                if (arg_boot) {

+                if (arg_start_mode == START_BOOT) {

                         if (path_is_os_tree(arg_directory) <= 0) {

                                 log_error("Directory %s doesn't look like an OS root directory (os-release file is missing). Refusing.", arg_directory);

                                 r = -EINVAL;

@@ -4109,7 +4138,19 @@ int main(int argc, char *argv[]) {

                         if (!barrier_place_and_sync(&barrier))

                                 _exit(EXIT_FAILURE);

-                        if (arg_boot) {

+                        if (arg_start_mode == START_PID2) {

+                                r = stub_pid1(arg_uuid);

+                                if (r < 0)

+                                {

+                                        log_error_errno(r, "Failed to start as PID2: %m");

+                                        _exit(EXIT_FAILURE);

+                                }

+                        }

+

+                        log_close();

+                        (void) fdset_close_others(fds);

+

+                        if (arg_start_mode == START_BOOT) {

                                 char **a;

                                 size_t l;

@@ -4135,6 +4176,7 @@ int main(int argc, char *argv[]) {

                                 execle("/bin/sh", "-sh", NULL, env_use);

                         }

+                        log_open();

                         log_error_errno(errno, "execv() failed: %m");

                         _exit(EXIT_FAILURE);

                 }

@@ -4210,7 +4252,7 @@ int main(int argc, char *argv[]) {

                                         goto finish;

                                 }

-                                if (arg_boot) {

+                                if (arg_start_mode == START_BOOT) {

                                         /* Try to kill the init system on SIGINT or SIGTERM */

                                         sd_event_add_signal(event, NULL, SIGINT, on_orderly_shutdown, UINT32_TO_PTR(pid));

                                         sd_event_add_signal(event, NULL, SIGTERM, on_orderly_shutdown, UINT32_TO_PTR(pid));