[RFC bpf-next v5] bpf: Force to MPTCP

[Paul Moore]

On Tue, Jul 18, 2023 at 11:21 AM Geliang Tang <geliang.tang at suse.com> wrote:
>
> As is described in the "How to use MPTCP?" section in MPTCP wiki [1]:
>
> "Your app can create sockets with IPPROTO_MPTCP as the proto:
> ( socket(AF_INET, SOCK_STREAM, IPPROTO_MPTCP); ). Legacy apps can be
> forced to create and use MPTCP sockets instead of TCP ones via the
> mptcpize command bundled with the mptcpd daemon."
>
> But the mptcpize (LD_PRELOAD technique) command has some limitations
> [2]:
>
>  - it doesn't work if the application is not using libc (e.g. GoLang
> apps)
>  - in some envs, it might not be easy to set env vars / change the way
> apps are launched, e.g. on Android
>  - mptcpize needs to be launched with all apps that want MPTCP: we could
> have more control from BPF to enable MPTCP only for some apps or all the
> ones of a netns or a cgroup, etc.
>  - it is not in BPF, we cannot talk about it at netdev conf.
>
> So this patchset attempts to use BPF to implement functions similer to
> mptcpize.
>
> The main idea is add a hook in sys_socket() to change the protocol id
> from IPPROTO_TCP (or 0) to IPPROTO_MPTCP.
>
> [1]
> https://github.com/multipath-tcp/mptcp_net-next/wiki
> [2]
> https://github.com/multipath-tcp/mptcp_net-next/issues/79
>
> v5:
>  - add bpf_mptcpify helper.
>
> v4:
>  - use lsm_cgroup/socket_create
>
> v3:
>  - patch 8: char cmd[128]; -> char cmd[256];
>
> v2:
>  - Fix build selftests errors reported by CI
>
> Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/79
> Signed-off-by: Geliang Tang <geliang.tang at suse.com>
> ---
>  include/linux/bpf.h                           |   1 +
>  include/linux/lsm_hook_defs.h                 |   2 +-
>  include/linux/security.h                      |   6 +-
>  include/uapi/linux/bpf.h                      |   7 +
>  kernel/bpf/bpf_lsm.c                          |   2 +
>  net/mptcp/bpf.c                               |  20 +++
>  net/socket.c                                  |   4 +-
>  security/apparmor/lsm.c                       |   8 +-
>  security/security.c                           |   2 +-
>  security/selinux/hooks.c                      |   6 +-
>  tools/include/uapi/linux/bpf.h                |   7 +
>  .../testing/selftests/bpf/prog_tests/mptcp.c  | 128 ++++++++++++++++--
>  tools/testing/selftests/bpf/progs/mptcpify.c  |  17 +++
>  13 files changed, 187 insertions(+), 23 deletions(-)
>  create mode 100644 tools/testing/selftests/bpf/progs/mptcpify.c

...

> diff --git a/security/security.c b/security/security.c
> index b720424ca37d..bbebcddce420 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -4078,7 +4078,7 @@ EXPORT_SYMBOL(security_unix_may_send);
>   *
>   * Return: Returns 0 if permission is granted.
>   */
> -int security_socket_create(int family, int type, int protocol, int kern)
> +int security_socket_create(int *family, int *type, int *protocol, int kern)
>  {
>         return call_int_hook(socket_create, 0, family, type, protocol, kern);
>  }

Using the LSM to change the protocol family is not something we want
to allow.  I'm sorry, but you will need to take a different approach.

-- 
paul-moore.com