netdev - Re: CAP_NET_ADMIN check in tc_ctl_action() makes it not allowed for user ns root

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Message-ID: <CAM_iQpUpQ_b5UbKRA+crSmhYeDN8PFE-KaBOp9je-zOkhg=3Kg@mail.gmail.com>
Date:   Mon, 7 Jun 2021 21:22:51 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     tianyu zhou <tyjoe.linux@...il.com>
Cc:     Jamal Hadi Salim <jhs@...atatu.com>, Jiri Pirko <jiri@...nulli.us>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: CAP_NET_ADMIN check in tc_ctl_action() makes it not allowed for
 user ns root

On Tue, Jun 1, 2021 at 1:17 AM tianyu zhou <tyjoe.linux@...il.com> wrote:
>
> Hi, from commit "net: Allow tc changes in user
> namespaces"(SHA:4e8bbb819d1594a01f91b1de83321f68d3e6e245) I learned
> that "root in a user namespace may set tc rules inside that
> namespace".
>
> I do see the CAP_NET_ADMIN check in tc_* functions has changed from
> capable() to ns_capable() (which is now in term of
> netlink_ns_capable())
>
> However, in function tc_ctl_action(), the check for CAP_NET_ADMIN is
> still netlink_capable which does not allow user ns root to pass this
> check.
>
> static int tc_ctl_action(struct sk_buff *skb, struct nlmsghdr *n,
>              struct netlink_ext_ack *extack)
> {
>     ...
>     if ((n->nlmsg_type != RTM_GETACTION) &&
>         !netlink_capable(skb, CAP_NET_ADMIN))
>         return -EPERM;
>     ...
> }
>
> So is this a check missing changing for user ns?

It seems so, I do not see TC action is any different with other
TC objects here. So feel free to send a patch.

Thanks.