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

[Dmitry Torokhov]

On Mon, Aug 8, 2016 at 2:08 PM, Eric W. Biederman <ebiederm@xxxxxxxxxxxx> wrote:
> Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx> 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@xxxxxxxxxxxx>
>
> Overall this seems reasonable.  However I am not a fan of your error
> handling.
>
>> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>
>> ---
>>
>> 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).

Thanks.

-- 
Dmitry