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From: Christian Brauner <christian.brauner@canonical.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: davem@davemloft.net, netdev@vger.kernel.org,
	linux-kernel@vger.kernel.org, avagin@virtuozzo.com,
	ktkhai@virtuozzo.com, serge@hallyn.com,
	gregkh@linuxfoundation.org
Subject: Re: [PATCH net-next 2/2 v3] netns: restrict uevents
Date: Sat, 28 Apr 2018 21:13:05 +0200	[thread overview]
Message-ID: <20180428191304.GB13787@gmail.com> (raw)
In-Reply-To: <87po2k7gt9.fsf@xmission.com>

On Fri, Apr 27, 2018 at 11:30:26AM -0500, Eric W. Biederman wrote:
> Christian Brauner <christian.brauner@ubuntu.com> writes:
> > ---
> >  lib/kobject_uevent.c | 140 ++++++++++++++++++++++++++++++-------------
> >  1 file changed, 99 insertions(+), 41 deletions(-)
> >
> > diff --git a/lib/kobject_uevent.c b/lib/kobject_uevent.c
> > index c3cb110f663b..d8ce5e6d83af 100644
> > --- a/lib/kobject_uevent.c
> > +++ b/lib/kobject_uevent.c
> >  
> > +static int uevent_net_broadcast_tagged(struct sock *usk,
> > +				       struct kobj_uevent_env *env,
> > +				       const char *action_string,
> > +				       const char *devpath)
> > +{
> > +	struct user_namespace *owning_user_ns = sock_net(usk)->user_ns;
> > +	struct sk_buff *skb = NULL;
> > +	int ret;
> > +
> > +	skb = alloc_uevent_skb(env, action_string, devpath);
> > +	if (!skb)
> > +		return -ENOMEM;
> > +
> > +	/* fix credentials */
> > +	if (owning_user_ns != &init_user_ns) {
> 
> Nit: This test is just a performance optimization as such is not
>       necessary.  That is we can safely unconditionally set the
>       credentials this way.

alloc_uevent_skb() will now set

	parms = &NETLINK_CB(skb);
	parms->creds.uid = GLOBAL_ROOT_UID;
	parms->creds.gid = GLOBAL_ROOT_GID;
	parms->dst_group = 1;
	parms->portid = 0;

explicitly. So repeating that initialization unconditionally here does
not make sense to me. Also, this hits map_uid_down() in user_namespace.c
which is a known-hotpath (Remember the extensive testing we did back for
uidmap limit bumping from 5 to 340.). And even though it might not
matter much in this case there's no need to hit this code. The condition
also make it obvious that only non-initial user namespace uevent sockets
need fixing.

Christian

> 
> > +		struct netlink_skb_parms *parms = &NETLINK_CB(skb);
> > +		kuid_t root_uid;
> > +		kgid_t root_gid;
> > +
> > +		/* fix uid */
> > +		root_uid = make_kuid(owning_user_ns, 0);
> > +		if (!uid_valid(root_uid))
> > +			root_uid = GLOBAL_ROOT_UID;
> > +		parms->creds.uid = root_uid;
> > +
> > +		/* fix gid */
> > +		root_gid = make_kgid(owning_user_ns, 0);
> > +		if (!gid_valid(root_gid))
> > +			root_gid = GLOBAL_ROOT_GID;
> > +		parms->creds.gid = root_gid;
> > +	}
> > +
> > +	ret = netlink_broadcast(usk, skb, 0, 1, GFP_KERNEL);
> > +	/* ENOBUFS should be handled in userspace */
> > +	if (ret == -ENOBUFS || ret == -ESRCH)
> > +		ret = 0;
> > +
> > +	return ret;
> > +}
> > +#endif

  reply	other threads:[~2018-04-28 19:13 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-27 10:23 [PATCH net-next 0/2] netns: uevent filtering Christian Brauner
2018-04-27 10:23 ` [PATCH net-next 1/2 v3] uevent: add alloc_uevent_skb() helper Christian Brauner
2018-04-27 16:39   ` Eric W. Biederman
2018-04-28 19:09     ` Christian Brauner
2018-04-27 10:23 ` [PATCH net-next 2/2 v3] netns: restrict uevents Christian Brauner
2018-04-27 16:30   ` Eric W. Biederman
2018-04-28 19:13     ` Christian Brauner [this message]
2018-04-27 16:27 ` [PATCH net-next 0/2] netns: uevent filtering Eric W. Biederman

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