linux-kernel - Re: [PATCH] net: make net namespace sysctls belong to container's owner

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Date:	Mon, 08 Aug 2016 16:48:40 -0500
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Al Viro <viro@...iv.linux.org.uk>,
	lkml <linux-kernel@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] net: make net namespace sysctls belong to container's owner

Dmitry Torokhov <dmitry.torokhov@...il.com> writes:

> On Mon, Aug 8, 2016 at 2:08 PM, Eric W. Biederman <ebiederm@...ssion.com> wrote:
>> Dmitry Torokhov <dmitry.torokhov@...il.com> writes:
>>
>>> If net namespace is attached to a user namespace let's make container's
>>> root owner of sysctls affecting said network namespace instead of global
>>> root.
>>>
>>> This also allows us to clean up net_ctl_permissions() because we do not
>>> need to fudge permissions anymore for the container's owner since it now
>>> owns the objects in question.
>>
>> Acked-by: "Eric W. Biederman" <ebiederm@...ssion.com>
>>
>> Overall this seems reasonable.  However I am not a fan of your error
>> handling.
>>
>>> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
>>> ---
>>>
>>> This helps when running Android CTS in a container, but I think it makes
>>> sense regardless.
>>
>>> +static void net_ctl_set_ownership(struct ctl_table_header *head,
>>> +                               struct ctl_table *table,
>>> +                               kuid_t *uid, kgid_t *gid)
>>> +{
>>> +     struct net *net = container_of(head->set, struct net, sysctls);
>>> +
>>> +     *uid = make_kuid(net->user_ns, 0);
>>> +     if (!uid_valid(*uid))
>>> +             *uid = GLOBAL_ROOT_UID;
>>> +
>>> +     *gid = make_kgid(net->user_ns, 0);
>>> +     if (!gid_valid(*gid))
>>> +             *gid = GLOBAL_ROOT_GID;
>>
>> This code should eiter be:
>>         *uid = make_kuid(net->user_ns, 0);
>>         *gid = make_kgid(net->user_ns, 0);
>>
>> Or it should be:
>>         tmp_uid = make_kuid(net->user_ns, 0);
>>         if (uid_valid(tmp_uid))
>>                 *uid = tmp_uid;
>>
>>         tmp_gid = make_kgid(net->user_ns, 0);
>>         if (gid_valid(tmp_gid))
>>                 *gid = tmp_gid;
>>
>> It is just very fragile to assume to know what uid and gid
>> would be if this code fails.
>>
>> As of v4.8-rc1 INVALID_UID and INVALID_GID can be set in inode->i_uid
>> and inode->i_gid without causing horrible vfs confusion (making the
>> first option viable), but I expect with the mention of Android you want
>> to backport this so I will ask that you ask to implement the error
>> handling that doesn't assume you know better than the generic code.
>>
>> If you don't have a better value to set something to it really should be
>> left alone.
>
> OK, fair enough. I will adopt the 2nd option and will resubmit. I need
> to also test without net namespaces support (my other change blows up
> because we are getting half-initialized init_net structure when
> namespaces are disabled).

No rush.  I will be out on vacation for the next couple of weeks.

Eric