Documenting reboot(2) changes for PID namespace in 3.9

Documenting reboot(2) changes for PID namespace in 3.9

[Michael Kerrisk (man-pages)]

Li,

Regarding your commit 923c7538236564c46ee80c253a416705321f13e3 , I
plan to apply the following patch to the reboot(2) manual page. Does
it look okay to you?

Thanks,

Michael

diff --git a/man2/reboot.2 b/man2/reboot.2
index 8347870..1c17b85 100644
--- a/man2/reboot.2
+++ b/man2/reboot.2
@@ -24,7 +24,7 @@
 .\" Modified, 27 May 2004, Michael Kerrisk <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
 .\"     Added notes on capability requirements
 .\"
-.TH REBOOT 2 2010-10-31 "Linux" "Linux Programmer's Manual"
+.TH REBOOT 2 2013-03-12 "Linux" "Linux Programmer's Manual"
 .SH NAME
 reboot \- reboot or enable/disable Ctrl-Alt-Del
 .SH SYNOPSIS
@@ -147,6 +147,26 @@ For the i386 architecture, the additional
argument does not do
 anything at present (2.1.122), but the type of reboot can be
 determined by kernel command-line arguments ("reboot=...") to be
 either warm or cold, and either hard or through the BIOS.
+.SS Behavior inside PID namespaces
+.\" commit commit 923c7538236564c46ee80c253a416705321f13e3
+Since Linux 3.9, when
+.BR reboot ()
+is called from a PID namespace (see
+.BR pid_namespaces (7))
+other than the initial PID namespace,
+the effect of the call is to send a signal to the namespace "init" process.
+.BR LINUX_REBOOT_CMD_RESTART
+and
+.BR LINUX_REBOOT_CMD_RESTART2
+cause a
+.BR SIGHUP
+signal to be sent.
+.BR LINUX_REBOOT_CMD_POWER_OFF
+and
+.BR LINUX_REBOOT_CMD_HALT
+cause a
+.B SIGINT
+signal to be sent.
 .SH RETURN VALUE
 For the values of
 .I cmd

Re: Documenting reboot(2) changes for PID namespace in 3.9

[Eric W. Biederman]

"Michael Kerrisk (man-pages)" <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> writes:

> Li,
>
> Regarding your commit 923c7538236564c46ee80c253a416705321f13e3 , I
> plan to apply the following patch to the reboot(2) manual page. Does
> it look okay to you?

You have documented the behavior as of 3.4.

The change in 3.9 is to allow that same behavior in a pid_namespace
created with a user namespace.  Aka in 3.9 the permission
check changed from capable(CAP_SYS_BOOT)  to ns_capable(pid_ns->user_ns, CAP_SYS_BOOT);

Eric

> Thanks,
>
> Michael
>
> diff --git a/man2/reboot.2 b/man2/reboot.2
> index 8347870..1c17b85 100644
> --- a/man2/reboot.2
> +++ b/man2/reboot.2
> @@ -24,7 +24,7 @@
>  .\" Modified, 27 May 2004, Michael Kerrisk <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
>  .\"     Added notes on capability requirements
>  .\"
> -.TH REBOOT 2 2010-10-31 "Linux" "Linux Programmer's Manual"
> +.TH REBOOT 2 2013-03-12 "Linux" "Linux Programmer's Manual"
>  .SH NAME
>  reboot \- reboot or enable/disable Ctrl-Alt-Del
>  .SH SYNOPSIS
> @@ -147,6 +147,26 @@ For the i386 architecture, the additional
> argument does not do
>  anything at present (2.1.122), but the type of reboot can be
>  determined by kernel command-line arguments ("reboot=...") to be
>  either warm or cold, and either hard or through the BIOS.
> +.SS Behavior inside PID namespaces
> +.\" commit commit 923c7538236564c46ee80c253a416705321f13e3
> +Since Linux 3.9, when
               ^^^ 3.4
> +.BR reboot ()
> +is called from a PID namespace (see
> +.BR pid_namespaces (7))
> +other than the initial PID namespace,
> +the effect of the call is to send a signal to the namespace "init" process.
> +.BR LINUX_REBOOT_CMD_RESTART
> +and
> +.BR LINUX_REBOOT_CMD_RESTART2
> +cause a
> +.BR SIGHUP
> +signal to be sent.
> +.BR LINUX_REBOOT_CMD_POWER_OFF
> +and
> +.BR LINUX_REBOOT_CMD_HALT
> +cause a
> +.B SIGINT
> +signal to be sent.
>  .SH RETURN VALUE
>  For the values of
>  .I cmd

Re: Documenting reboot(2) changes for PID namespace in 3.9

[Michael Kerrisk (man-pages)]

On Tue, Mar 12, 2013 at 8:20 AM, Eric W. Biederman
<ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org> wrote:
> "Michael Kerrisk (man-pages)" <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> writes:
>
>> Li,
>>
>> Regarding your commit 923c7538236564c46ee80c253a416705321f13e3 , I
>> plan to apply the following patch to the reboot(2) manual page. Does
>> it look okay to you?
>
> You have documented the behavior as of 3.4.

Thanks Eric. I tweaked the version number.

> The change in 3.9 is to allow that same behavior in a pid_namespace
> created with a user namespace.  Aka in 3.9 the permission
> check changed from capable(CAP_SYS_BOOT)  to ns_capable(pid_ns->user_ns, CAP_SYS_BOOT);

Does anything need to be detailed about this in the man page then?

Thanks,

Michael



>
> Eric
>
>> Thanks,
>>
>> Michael
>>
>> diff --git a/man2/reboot.2 b/man2/reboot.2
>> index 8347870..1c17b85 100644
>> --- a/man2/reboot.2
>> +++ b/man2/reboot.2
>> @@ -24,7 +24,7 @@
>>  .\" Modified, 27 May 2004, Michael Kerrisk <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
>>  .\"     Added notes on capability requirements
>>  .\"
>> -.TH REBOOT 2 2010-10-31 "Linux" "Linux Programmer's Manual"
>> +.TH REBOOT 2 2013-03-12 "Linux" "Linux Programmer's Manual"
>>  .SH NAME
>>  reboot \- reboot or enable/disable Ctrl-Alt-Del
>>  .SH SYNOPSIS
>> @@ -147,6 +147,26 @@ For the i386 architecture, the additional
>> argument does not do
>>  anything at present (2.1.122), but the type of reboot can be
>>  determined by kernel command-line arguments ("reboot=...") to be
>>  either warm or cold, and either hard or through the BIOS.
>> +.SS Behavior inside PID namespaces
>> +.\" commit commit 923c7538236564c46ee80c253a416705321f13e3
>> +Since Linux 3.9, when
>                ^^^ 3.4
>> +.BR reboot ()
>> +is called from a PID namespace (see
>> +.BR pid_namespaces (7))
>> +other than the initial PID namespace,
>> +the effect of the call is to send a signal to the namespace "init" process.
>> +.BR LINUX_REBOOT_CMD_RESTART
>> +and
>> +.BR LINUX_REBOOT_CMD_RESTART2
>> +cause a
>> +.BR SIGHUP
>> +signal to be sent.
>> +.BR LINUX_REBOOT_CMD_POWER_OFF
>> +and
>> +.BR LINUX_REBOOT_CMD_HALT
>> +cause a
>> +.B SIGINT
>> +signal to be sent.
>>  .SH RETURN VALUE
>>  For the values of
>>  .I cmd



-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Author of "The Linux Programming Interface"; http://man7.org/tlpi/