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

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Date:   Fri, 25 Mar 2022 08:29:25 -0500
From:   "Eric W. Biederman" <ebiederm@...ssion.com>
To:     Petr Vorel <pvorel@...e.cz>
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?

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);