kern/120753: Zombie jails (jailed child process exits while
non-jailed parent is alive)
Piotr Koper
piotr.koper at gmail.com
Sun Feb 17 13:20:02 UTC 2008
>Number: 120753
>Category: kern
>Synopsis: Zombie jails (jailed child process exits while non-jailed parent is alive)
>Confidential: no
>Severity: non-critical
>Priority: low
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Sun Feb 17 13:20:02 UTC 2008
>Closed-Date:
>Last-Modified:
>Originator: Piotr Koper
>Release: 6.2-RELEASE, 6.3-RELEASE
>Organization:
>Environment:
FreeBSD node01 6.3-RELEASE FreeBSD 6.3-RELEASE #7: Sun Feb 3 03:56:47 CET 2008 root at node01:/usr/obj/usr/src/sys/NODE i386
>Description:
1. fork ()
2. child: jail (...)
3. child: execv (...)
4. parent: sleep (...)
So, when parent sleeps, child has already died, but:
$ ps auxw | grep J
root 21566 0.0 0.0 0 0 p2 ZJ 1:53PM 0:00.00 <defunct>
$ jls
JID IP Address Hostname Path
7 127.0.0.1 jail-fork /
$
When the parent exits, the jail disappears.
$ jls
$
But when you double fork the jail disappears as soon as the child process dies:
1. fork ()
2. child: fork ()
3. child: parent: exit ()
4. child: child: jail (...)
5. child: child: execv (...)
6. parent: sleep (10)
$ jls
$
See "How to repeat".
>How-To-Repeat:
Compile the code bellow and try two scenario:
1. $ ./jail-fork & sleep 1 ; jls ; ps auxw | grep J
2. $ ./jail-fork double-fork & sleep 1 ; jls ; ps auxw | grep J
For 1: you sees:
root 24113 0.0 0.0 0 0 p2 ZJ 2:06PM 0:00.00 <defunct>
For 2: everything is ok - no zombie process
<!-- file:jail-fork.c --!>
#include <arpa/inet.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/param.h>
#include <sys/types.h>
#include <sys/jail.h>
#include <unistd.h>
int
main (int argc, char *argv[])
{
struct in_addr in;
struct jail j;
char *j_argv[] = { "/bin/ls", "/COPYRIGHT" };
j.version = 0;
j.path = "/";
j.hostname = "jail-fork";
if (inet_aton ("127.0.0.1", &in) == 0)
perror ("inet_addr");
j.ip_number = ntohl (in.s_addr);
/* Just fork, we'd like to create a background jailed process. */
if (fork () == 0)
{
/* Fork again if additional arguments supplied */
if (argc > 1 && fork () > 0)
exit (0);
if (jail (&j) < 0)
perror ("jail");
execv (j_argv[0], j_argv);
perror ("execv");
}
sleep (3);
return 0;
}
>Fix:
>Release-Note:
>Audit-Trail:
>Unformatted:
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