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.
> !ns_capable(net->user_ns, CAP_NET_BIND_SERVICE))
> goto out;
>
