2019-11-20 13:03:36

by Christian Brauner

[permalink] [raw]
Subject: [PATCH] clone.2: Mention that CLONE_PARENT is off-limits for inits

From: Christian Brauner <[email protected]>

The CLONE_PARENT flag cannot but used by init processes. Let's mention
this in the manpages to prevent suprises.

Signed-off-by: Christian Brauner <[email protected]>
---
man2/clone.2 | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/man2/clone.2 b/man2/clone.2
index f0f29d6f1..aa98ab79b 100644
--- a/man2/clone.2
+++ b/man2/clone.2
@@ -646,6 +646,13 @@ if
.B CLONE_PARENT
is set, then the parent of the calling process, rather than the
calling process itself, will be signaled.
+.IP
+The kernel will not allow global init and init processes in pid
+namespaces to use the
+.B CLONE_PARENT
+flag. This is done to prevent the creation of multi-rooted process
+trees. It also avoids unreapable zombies in the initial pid
+namespace.
.TP
.BR CLONE_PARENT_SETTID " (since Linux 2.5.49)"
Store the child thread ID at the location pointed to by
--
2.24.0



Subject: Re: [PATCH] clone.2: Mention that CLONE_PARENT is off-limits for inits

Hello Christian,

On 11/20/19 11:45 AM, Christian Brauner wrote:
> From: Christian Brauner <[email protected]>
>
> The CLONE_PARENT flag cannot but used by init processes. Let's mention
> this in the manpages to prevent suprises.
>
> Signed-off-by: Christian Brauner <[email protected]>
> ---
> man2/clone.2 | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/man2/clone.2 b/man2/clone.2
> index f0f29d6f1..aa98ab79b 100644
> --- a/man2/clone.2
> +++ b/man2/clone.2
> @@ -646,6 +646,13 @@ if
> .B CLONE_PARENT
> is set, then the parent of the calling process, rather than the
> calling process itself, will be signaled.
> +.IP
> +The kernel will not allow global init and init processes in pid
> +namespaces to use the
> +.B CLONE_PARENT
> +flag. This is done to prevent the creation of multi-rooted process
> +trees. It also avoids unreapable zombies in the initial pid
> +namespace.
> .TP
> .BR CLONE_PARENT_SETTID " (since Linux 2.5.49)"
> Store the child thread ID at the location pointed to by

Thank. I applied, and then tweaked the text a little,
and noted the associated EINVAL error. In the end, the
change is as below.

Cheers,

Michael

index 60e746151..382f6b791 100644
--- a/man2/clone.2
+++ b/man2/clone.2
@@ -648,6 +648,14 @@ if
.B CLONE_PARENT
is set, then the parent of the calling process, rather than the
calling process itself, will be signaled.
+.IP
+The
+.B CLONE_PARENT
+flag can't be used in clone calls by the
+global init process (PID 1 in the initial PID namespace)
+and init processes in other PID namespaces.
+This restriction prevents the creation of multi-rooted process trees
+as well as the creation of unreapable zombies in the initial PID namespace.
.TP
.BR CLONE_PARENT_SETTID " (since Linux 2.5.49)"
Store the child thread ID at the location pointed to by
@@ -1273,6 +1281,11 @@ were specified in the
.IR flags
mask.
.TP
+.BR EINVAL " (since Linux 2.6.32)"
+.\" commit 123be07b0b399670a7cc3d82fef0cb4f93ef885c
+.BR CLONE_PARENT
+was specified, and the caller is an init process.
+.TP
.B EINVAL
Returned by the glibc
.BR clone ()



--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/

2019-11-21 11:28:56

by Christian Brauner

[permalink] [raw]
Subject: Re: [PATCH] clone.2: Mention that CLONE_PARENT is off-limits for inits

On Thu, Nov 21, 2019 at 10:53:50AM +0100, Michael Kerrisk (man-pages) wrote:
> Hello Christian,
>
> On 11/20/19 11:45 AM, Christian Brauner wrote:
> > From: Christian Brauner <[email protected]>
> >
> > The CLONE_PARENT flag cannot but used by init processes. Let's mention
> > this in the manpages to prevent suprises.
> >
> > Signed-off-by: Christian Brauner <[email protected]>
> > ---
> > man2/clone.2 | 7 +++++++
> > 1 file changed, 7 insertions(+)
> >
> > diff --git a/man2/clone.2 b/man2/clone.2
> > index f0f29d6f1..aa98ab79b 100644
> > --- a/man2/clone.2
> > +++ b/man2/clone.2
> > @@ -646,6 +646,13 @@ if
> > .B CLONE_PARENT
> > is set, then the parent of the calling process, rather than the
> > calling process itself, will be signaled.
> > +.IP
> > +The kernel will not allow global init and init processes in pid
> > +namespaces to use the
> > +.B CLONE_PARENT
> > +flag. This is done to prevent the creation of multi-rooted process
> > +trees. It also avoids unreapable zombies in the initial pid
> > +namespace.
> > .TP
> > .BR CLONE_PARENT_SETTID " (since Linux 2.5.49)"
> > Store the child thread ID at the location pointed to by
>
> Thank. I applied, and then tweaked the text a little,
> and noted the associated EINVAL error. In the end, the
> change is as below.

Thanks!
Christian