linux-kernel - Re: [PATCH 1/9] Add a user_namespace as creator/owner of uts

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Date:	Fri, 18 Feb 2011 17:57:41 +0100
From:	Daniel Lezcano <daniel.lezcano@...e.fr>
To:	"Serge E. Hallyn" <serge@...lyn.com>
CC:	xemul@...allels.com, containers@...ts.linux-foundation.org,
	kernel list <linux-kernel@...r.kernel.org>,
	dhowells@...hat.com, LSM <linux-security-module@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Kees Cook <kees.cook@...onical.com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Michael Kerrisk <mtk.manpages@...il.com>
Subject: Re: [PATCH 1/9] Add a user_namespace as creator/owner of uts_namespace

On 02/17/2011 04:02 PM, Serge E. Hallyn wrote:
> copy_process() handles CLONE_NEWUSER before the rest of the
> namespaces.  So in the case of clone(CLONE_NEWUSER|CLONE_NEWUTS)
> the new uts namespace will have the new user namespace as its
> owner.  That is what we want, since we want root in that new
> userns to be able to have privilege over it.
>
> Changelog:
> 	Feb 15: don't set uts_ns->user_ns if we didn't create
> 		a new uts_ns.
>
> Signed-off-by: Serge E. Hallyn<serge.hallyn@...onical.com>

Acked-by: Daniel Lezcano <daniel.lezcano@...e.fr>

A couple of comments.

> ---
>   include/linux/utsname.h |    3 +++
>   init/version.c          |    2 ++
>   kernel/nsproxy.c        |    5 +++++
>   kernel/user.c           |    8 ++++++--
>   kernel/utsname.c        |    4 ++++
>   5 files changed, 20 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/utsname.h b/include/linux/utsname.h
> index 69f3997..85171be 100644
> --- a/include/linux/utsname.h
> +++ b/include/linux/utsname.h
> @@ -37,9 +37,12 @@ struct new_utsname {
>   #include<linux/nsproxy.h>
>   #include<linux/err.h>
>
> +struct user_namespace;
> +
>   struct uts_namespace {
>   	struct kref kref;
>   	struct new_utsname name;
> +	struct user_namespace *user_ns;
>   };
>   extern struct uts_namespace init_uts_ns;
>
> diff --git a/init/version.c b/init/version.c
> index adff586..97bb86f 100644
> --- a/init/version.c
> +++ b/init/version.c
> @@ -21,6 +21,7 @@ extern int version_string(LINUX_VERSION_CODE);
>   int version_string(LINUX_VERSION_CODE);
>   #endif
>
> +extern struct user_namespace init_user_ns;
>   struct uts_namespace init_uts_ns = {
>   	.kref = {
>   		.refcount	= ATOMIC_INIT(2),
> @@ -33,6 +34,7 @@ struct uts_namespace init_uts_ns = {
>   		.machine	= UTS_MACHINE,
>   		.domainname	= UTS_DOMAINNAME,
>   	},
> +	.user_ns =&init_user_ns,
>   };
>   EXPORT_SYMBOL_GPL(init_uts_ns);
>
> diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
> index f74e6c0..034dc2e 100644
> --- a/kernel/nsproxy.c
> +++ b/kernel/nsproxy.c
> @@ -74,6 +74,11 @@ static struct nsproxy *create_new_namespaces(unsigned long flags,
>   		err = PTR_ERR(new_nsp->uts_ns);
>   		goto out_uts;
>   	}
> +	if (new_nsp->uts_ns != tsk->nsproxy->uts_ns) {
> +		put_user_ns(new_nsp->uts_ns->user_ns);
> +		new_nsp->uts_ns->user_ns = task_cred_xxx(tsk, user)->user_ns;
> +		get_user_ns(new_nsp->uts_ns->user_ns);
> +	}

IMO you should add a comment telling this code assume create_user_ns was 
called before (via copy_cred).

>
>   	new_nsp->ipc_ns = copy_ipcs(flags, tsk->nsproxy->ipc_ns);
>   	if (IS_ERR(new_nsp->ipc_ns)) {

[ ... ]

>   static struct uts_namespace *create_uts_ns(void)
>   {
> @@ -40,6 +41,8 @@ static struct uts_namespace *clone_uts_ns(struct uts_namespace *old_ns)
>
>   	down_read(&uts_sem);
>   	memcpy(&ns->name,&old_ns->name, sizeof(ns->name));
> +	ns->user_ns = old_ns->user_ns;
> +	get_user_ns(ns->user_ns);

ns->user_ns = get_user_ns(old_ns->user_ns);

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