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Date:      Wed, 21 Feb 2024 11:55:25 +0000
From:      bugzilla-noreply@freebsd.org
To:        bugs@FreeBSD.org
Subject:   [Bug 277210] jail(8): exec.clean retrieves PWD from user info (can cause services to crash on jail start-up)
Message-ID:  <bug-277210-227@https.bugs.freebsd.org/bugzilla/>
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D277210

            Bug ID: 277210
           Summary: jail(8): exec.clean retrieves PWD from user info (can
                    cause services to crash on jail start-up)
           Product: Base System
           Version: Unspecified
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Many People
          Priority: ---
         Component: bin
          Assignee: bugs@FreeBSD.org
          Reporter: johannes.kunde@gmail.com

I recently ran into a problem where one of my services, configured via rc(8=
),=20
failed to start, but only if the corresponding jail was (re)started as a wh=
ole.
The same service (re)started without problems when running 'service foo sta=
rt'.
Digging into the problem, I found out that in case 'exec.clean' has been se=
t in=20
jail.conf(5), PWD is set to '/root' (only root:wheel can read here) when
(re)starting the jail,=20
but is set to '/' when running 'service foo start' from within the running
jail.=20
I think this behavior is caused by the following lines:
https://github.com/freebsd/freebsd-src/blob/main/usr.sbin/jail/command.c#L7=
27-L797.

It is also not documented in the manpage that a chdir(2) happens with
'exec.clean'.

So far, I've found two ways to overcome this behavior. One is to omit
'exec.clean' in=20
jail.conf(5), the other is to set '${name}_chdir=3D"/"' in the corresponding
rc(8) script.

However, I wanted to file this bug and discuss the problem, as I'm uncertai=
n if
this behavior=20
is intended. When running the very same service on a FreeBSD host system (n=
ot
in a jail)=20
it starts up normally, because PWD will be "/" in any case. It's also quite
hard to trace=20
that issue down to the above lines, as there is no obvious error message ot=
her
than what=20
is printed out by the affected service itself.

The problem can be easily reproduced with the below C program and rc(8) scr=
ipt:

Compile the program with 'cc -o getcwd getcwd.c' and copy it to
'/usr/local/sbin'.



#include <unistd.h>
#include <limits.h>
#include <syslog.h>

int main() {
        char cwd[PATH_MAX];
                if (getcwd(cwd, sizeof(cwd)) !=3D NULL) {
                        syslog(LOG_DEBUG, "Current working dir: %s\n", cwd);
                } else {
                        syslog(LOG_DEBUG, "getcwd() error");
                        return 1;
                }
        return 0;
}



Copy the following script to '/usr/local/etc/rc.d/getcwd' and run 'chmod +x
/usr/local/etc/rc.d/getcwd'.



#!/bin/sh
#
# PROVIDE: getcwd

. /etc/rc.subr

name=3D"getcwd"
rcvar=3D"getcwd_enable"
command=3D"/usr/local/sbin/${name}"

load_rc_config $name
: ${getcwd_enable:=3DNO}

run_rc_command "$1"



Run 'sysrc getcwd_enable=3D"YES"'

Now do the following:
1. Restart the jail
2. Run 'service getcwd start'
3. Take a look at '/var/log/debug.log'


NOTE: This behavior is not bound to or related to any specific Jail-Manager.

--=20
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