> On 24 Feb 2016, at 05:06, Tom Herbert <t...@herbertland.com> wrote:
>
> On Tue, Feb 23, 2016 at 7:27 AM, Gilberto Bertin
> <gilberto.ber...@gmail.com> wrote:
>> This series introduces support for the SO_BINDTOSUBNET socket option, which
>> allows a listener socket to bind to a subnet instead of * or a single
>> address.
>>
>> Motivation:
>> consider a set of servers, each one with thousands and thousands of IP
>> addresses. Since assigning /32 or /128 IP individual addresses would be
>> inefficient, one solution can be assigning subnets using local routes
>> (with 'ip route add local').
>>
> Hi Gilberto,
>
> The concept is certainly relevant, but allowing binds by subnet seems
> arbitrary. I can imagine that someone might want to bind to a list of
> addresses, list of interfaces, list of subnets, or complex
> combinations like a subnet on one interface, and list of addresses on
> another. So I wonder if this is another use case for a BPF program on
> a listener socket, like a program for a scoring function. Maybe this
> could even combined with BPF SO_REUSERPORT somehow?
>
> Tom
Hi Tom,
I have a working POC of the patch that adds support for BPF into the
compute_score function, and I would like to share some thoughts about
advantages and disadvantages of both solutions.
First, setup.
SO_BINDTOSUBET:
- add this to some_server.c:
subnet.net = addr.s_addr;
subnet.plen = 24
setsockopt(sock, SOL_SOCKET, SO_BINDTOSUBNET, &subnet, sizeof(subnet));
and you are done. Your server will accept all connections from the
specified subnet.
BPF_LISTENER_FILTER:
- write a bpf filter like this:
SEC("socket_bpf")
int bpf_prog1(struct __sk_buff *skb)
{
unsigned int daddr;
daddr = load_word(skb, ETH_HLEN + offsetof(struct iphdr, daddr));
if (/* daddr matches subnet */) {
return -1; //accept
}
return 0; // reject
}
- compile it:
$ clang -target bpf -c -o socket_bpf.o socket_bpf.c
- add this to your server.c:
bpf_load_file("/path/to/socket_bpf.o");
setsockopt(sock, SOL_SOCKET, SO_ATTACH_BPF, prog_fd,
sizeof(prog_fd[0]));
- link your server with a couple of libbpf libraries (I'm
using the kernel ones from samples/bpf) and -lelf
And this is still simplified (since instead of hardcoding the subnet
into the bpf filter it would be preferable to use maps).
thoughts:
- SO_BINDTOSUBNET is much simpler to configure than BPF
- BPF requires some external C libraries and I think it would not be
trivial to get it working with other languages than C/C++.
As an example, I have two working servers for SO_BINDTOSUBNET written
in Ruby and Go (since both these languages expose setsockopt), but it
would be necessary to write something that wrap the C libbpf to use
BPF
- I (personally) do not think SO_BINDTOSUBNET is that much arbitrary, I
see it more as the logical missing piece between * and a single
address when calling bind() (otherwise I think we should consider
arbitrary even SO_BINDTODEVICE)
That said, do you believe it could be an option to maybe have both these
options? I think that the ability to run BPF in the listening path is
really interesting, but it's probably an overkill for the bind-to-subnet
use case.
Thank you,
gilberto
