netdev - Re: [PATCH bpf-next v3 1/2] bpf: allow rewriting to ports under ip_unprivileged_port

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Date:   Tue, 26 Jan 2021 10:05:32 -0800
From:   Stanislav Fomichev <sdf@...gle.com>
To:     Martin KaFai Lau <kafai@...com>
Cc:     Netdev <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrey Ignatov <rdna@...com>
Subject: Re: [PATCH bpf-next v3 1/2] bpf: allow rewriting to ports under ip_unprivileged_port_start

On Tue, Jan 26, 2021 at 10:01 AM Martin KaFai Lau <kafai@...com> wrote:
>
> On Tue, Jan 26, 2021 at 08:51:03AM -0800, Stanislav Fomichev wrote:
> > At the moment, BPF_CGROUP_INET{4,6}_BIND hooks can rewrite user_port
> > to the privileged ones (< ip_unprivileged_port_start), but it will
> > be rejected later on in the __inet_bind or __inet6_bind.
> >
> > Let's add another return value to indicate that CAP_NET_BIND_SERVICE
> > check should be ignored. Use the same idea as we currently use
> > in cgroup/egress where bit #1 indicates CN. Instead, for
> > cgroup/bind{4,6}, bit #1 indicates that CAP_NET_BIND_SERVICE should
> > be bypassed.
> >
> > v3:
> > - Update description (Martin KaFai Lau)
> > - Fix capability restore in selftest (Martin KaFai Lau)
> >
> > v2:
> > - Switch to explicit return code (Martin KaFai Lau)
> >
>
> [ ... ]
>
> > @@ -499,7 +501,8 @@ int __inet_bind(struct sock *sk, struct sockaddr *uaddr, int addr_len,
> >
> >       snum = ntohs(addr->sin_port);
> >       err = -EACCES;
> > -     if (snum && inet_port_requires_bind_service(net, snum) &&
> > +     if (!(flags & BIND_NO_CAP_NET_BIND_SERVICE) &&
> > +         snum && inet_port_requires_bind_service(net, snum) &&
> The same change needs to be done on __inet6_bind()
> and also adds a test for IPv6 in patch 2.
Oh, damn, I did add the flag but forgot to handle it. Thanks for
catching this, will do!