From 92f6078aeadec4dfd0e4e9e2ef14b0f7794141cc Mon Sep 17 00:00:00 2001

From: Andrey Ulanov <aulanov@gmail.com>

Date: Mon, 12 Dec 2016 17:38:18 -0800

Subject: [PATCH] nspawn: when getting SIGCHLD make sure it's from the first

 child (#4855)

When getting SIGCHLD we should not assume that it was the first

child forked from system-nspawn that has died as it may also be coming

from an orphan process. This change adds a signal handler that ignores

SIGCHLD unless it came from the first containerized child - the real

child.

Before this change the problem can be reproduced as follows:

$ sudo systemd-nspawn --directory=/container-root --share-system

Press ^] three times within 1s to kill container.

[root@andreyu-coreos ~]# { true & } &

[1] 22201

[root@andreyu-coreos ~]#

Container root-fedora-latest terminated by signal KILL

(cherry picked from commit 6916b164642d8bb4938878f4284f8ee5ccf3efd6)

---

 src/nspawn/nspawn.c | 25 +++++++++++++++++++++++--

 1 file changed, 23 insertions(+), 2 deletions(-)

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

index 81573be95a..503265545b 100644

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

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

@@ -38,6 +38,7 @@

 #include <sys/personality.h>

 #include <sys/prctl.h>

 #include <sys/types.h>

+#include <sys/wait.h>

 #include <unistd.h>

 #include "sd-daemon.h"

@@ -2538,6 +2539,26 @@ static int on_orderly_shutdown(sd_event_source *s, const struct signalfd_siginfo

         return 0;

 }

+static int on_sigchld(sd_event_source *s, const struct signalfd_siginfo *ssi, void *userdata) {

+        for (;;) {

+                siginfo_t si = {};

+                if (waitid(P_ALL, 0, &si, WNOHANG|WNOWAIT|WEXITED) < 0)

+                        return log_error_errno(errno, "Failed to waitid(): %m");

+                if (si.si_pid == 0) /* No pending children. */

+                        break;

+                if (si.si_pid == PTR_TO_PID(userdata)) {

+                        /* The main process we care for has exited. Return from

+                         * signal handler but leave the zombie. */

+                        sd_event_exit(sd_event_source_get_event(s), 0);

+                        break;

+                }

+                /* Reap all other children. */

+                (void) waitid(P_PID, si.si_pid, &si, WNOHANG|WEXITED);

+        }

+

+        return 0;

+}

+

 static int determine_names(void) {

         int r;

@@ -3952,8 +3973,8 @@ static int run(int master,

                 sd_event_add_signal(event, NULL, SIGTERM, NULL, NULL);

         }

-        /* simply exit on sigchld */

-        sd_event_add_signal(event, NULL, SIGCHLD, NULL, NULL);

+        /* Exit when the child exits */

+        sd_event_add_signal(event, NULL, SIGCHLD, on_sigchld, PID_TO_PTR(*pid));

         if (arg_expose_ports) {

                 r = expose_port_watch_rtnl(event, rtnl_socket_pair[0], on_address_change, exposed, &rtnl);