Re: [PATCH bpf-next v9 1/4] bpf: Add update_socket_protocol hook

On 8/3/23 6:41 AM, Geliang Tang wrote:

Add a hook named update_socket_protocol in __sys_socket(), for bpf progs to attach to and update socket protocol. One user case is to force legacy TCP apps to create and use MPTCP sockets instead of TCP ones.

Define a mod_ret set named bpf_mptcp_fmodret_ids, add the hook update_socket_protocol into this set, and register it in bpf_mptcp_kfunc_init().

Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/79 Acked-by: Matthieu Baerts matthieu.baerts@tessares.net Signed-off-by: Geliang Tang geliang.tang@suse.com

---

net/mptcp/bpf.c | 17 +++++++++++++++++ net/socket.c | 24 ++++++++++++++++++++++++ 2 files changed, 41 insertions(+)

diff --git a/net/mptcp/bpf.c b/net/mptcp/bpf.c index 5a0a84ad94af..c43aee31014d 100644 --- a/net/mptcp/bpf.c +++ b/net/mptcp/bpf.c @@ -12,6 +12,23 @@ #include <linux/bpf.h> #include "protocol.h" +#ifdef CONFIG_BPF_JIT

Is this necessary? Most other register_btf_* functions do not have a config like this.

+BTF_SET8_START(bpf_mptcp_fmodret_ids) +BTF_ID_FLAGS(func, update_socket_protocol) +BTF_SET8_END(bpf_mptcp_fmodret_ids)

+static const struct btf_kfunc_id_set bpf_mptcp_fmodret_set = {

• .owner = THIS_MODULE,
• .set = &bpf_mptcp_fmodret_ids,

+};

+static int __init bpf_mptcp_kfunc_init(void) +{

• return register_btf_fmodret_id_set(&bpf_mptcp_fmodret_set);

+} +late_initcall(bpf_mptcp_kfunc_init); +#endif /* CONFIG_BPF_JIT */

• struct mptcp_sock *bpf_mptcp_sock_from_subflow(struct sock *sk) { if (sk && sk_fullsock(sk) && sk->sk_protocol == IPPROTO_TCP && sk_is_mptcp(sk))

diff --git a/net/socket.c b/net/socket.c index 2b0e54b2405c..9f98ced88ac5 100644 --- a/net/socket.c +++ b/net/socket.c @@ -1644,11 +1644,35 @@ struct file *__sys_socket_file(int family, int type, int protocol) return sock_alloc_file(sock, flags, NULL); } +/* A hook for bpf progs to attach to and update socket protocol.

• • A static noinline declaration here could cause the compiler to
• • optimize away the function. A global noinline declaration will
• • keep the definition, but may optimize away the callsite.
• • Therefore, __weak is needed to ensure that the call is still
• • emitted, by telling the compiler that we don't know what the
• • function might eventually be.
• • __diag_* below are needed to dismiss the missing prototype warning.
• */

+__diag_push(); +__diag_ignore_all("-Wmissing-prototypes",

•   "kfuncs which will be used in BPF programs");
  

+__weak noinline int update_socket_protocol(int family, int type, int protocol) +{

• return protocol;

+}

+__diag_pop();

• int __sys_socket(int family, int type, int protocol) { struct socket *sock; int flags;

• protocol = update_socket_protocol(family, type, protocol); sock = __sys_socket_create(family, type, protocol); if (IS_ERR(sock)) return PTR_ERR(sock);