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@xxxxxxxxxxxx> Acked-by: Yonghong Song <yonghong.song@xxxxxxxxx> Signed-off-by: Geliang Tang <geliang.tang@xxxxxxxx> --- net/mptcp/bpf.c | 15 +++++++++++++++ net/socket.c | 26 +++++++++++++++++++++++++- 2 files changed, 40 insertions(+), 1 deletion(-) diff --git a/net/mptcp/bpf.c b/net/mptcp/bpf.c index 5a0a84ad94af..8a16672b94e2 100644 --- a/net/mptcp/bpf.c +++ b/net/mptcp/bpf.c @@ -19,3 +19,18 @@ struct mptcp_sock *bpf_mptcp_sock_from_subflow(struct sock *sk) return NULL; } + +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); diff --git a/net/socket.c b/net/socket.c index 2b0e54b2405c..e9b2e754a103 100644 --- a/net/socket.c +++ b/net/socket.c @@ -1644,12 +1644,36 @@ 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", + "A fmod_ret entry point for 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; - sock = __sys_socket_create(family, type, protocol); + sock = __sys_socket_create(family, type, + update_socket_protocol(family, type, protocol)); if (IS_ERR(sock)) return PTR_ERR(sock); -- 2.35.3
