linux-kernel - Re: [PATCH 1/1] ns: Move MAX_PID_NS_LEVEL to ns

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Date:   Fri, 25 Mar 2022 17:04:13 +0100
From:   Petr Vorel <pvorel@...e.cz>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     linux-kernel@...r.kernel.org,
        Christian Brauner <christian@...uner.io>,
        Alexey Gladkov <legion@...nel.org>,
        "Serge E . Hallyn" <serge@...lyn.com>,
        Vasily Averin <vvs@...tuozzo.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 1/1] ns: Move MAX_PID_NS_LEVEL to ns_common.h, reuse it

> Petr Vorel <pvorel@...e.cz> writes:

> > Move MAX_PID_NS_LEVEL to ns_common.h and reuse it in check in
> > user_namespace.c.

> What is the motivation for this change?

> Is it just that there is a bare number in create_user_ns and that is a
> little ugly?  Or is there something more motivating this?

Well, nothing more than to have constant which gives some description.

Kind regards,
Petr

> Eric


> > Signed-off-by: Petr Vorel <pvorel@...e.cz>
> > ---
> > Hi Christian, all,

> > I don't see putting MAX_PID_NS_LEVEL into ns_common.h as an elegant
> > solution but IMHO better than use a hardwired number or redefinition in
> > user_namespace.h.

> > Kind regards,
> > Petr

> >  include/linux/ns_common.h     | 3 +++
> >  include/linux/pid_namespace.h | 3 ---
> >  kernel/user_namespace.c       | 2 +-
> >  3 files changed, 4 insertions(+), 4 deletions(-)

> > diff --git a/include/linux/ns_common.h b/include/linux/ns_common.h
> > index 0f1d024bd958..173fab9dadf7 100644
> > --- a/include/linux/ns_common.h
> > +++ b/include/linux/ns_common.h
> > @@ -4,6 +4,9 @@

> >  #include <linux/refcount.h>

> > +/* MAX_PID_NS_LEVEL is needed for limiting size of 'struct pid' */
> > +#define MAX_PID_NS_LEVEL 32
> > +
> >  struct proc_ns_operations;

> >  struct ns_common {
> > diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
> > index 07481bb87d4e..f814068012d0 100644
> > --- a/include/linux/pid_namespace.h
> > +++ b/include/linux/pid_namespace.h
> > @@ -11,9 +11,6 @@
> >  #include <linux/ns_common.h>
> >  #include <linux/idr.h>

> > -/* MAX_PID_NS_LEVEL is needed for limiting size of 'struct pid' */
> > -#define MAX_PID_NS_LEVEL 32
> > -
> >  struct fs_pin;

> >  struct pid_namespace {
> > diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c
> > index 5481ba44a8d6..6ea6e263403d 100644
> > --- a/kernel/user_namespace.c
> > +++ b/kernel/user_namespace.c
> > @@ -87,7 +87,7 @@ int create_user_ns(struct cred *new)
> >  	int ret, i;

> >  	ret = -ENOSPC;
> > -	if (parent_ns->level > 32)
> > +	if (parent_ns->level > MAX_PID_NS_LEVEL)
> >  		goto fail;

> >  	ucounts = inc_user_namespaces(parent_ns, owner);