bpf: Extend bpf_skc_to_mptcp_sock to MPTCP sock

Currently, bpf_skc_to_mptcp_sock() can only be used with sockets that
are MPTCP subflows: TCP sockets with tp->is_mptcp, created by the kernel
from an MPTCP socket (IPPROTO_MPTCP). Typically used with BPF sock_ops
operators.

Here, this helper is extended to support MPTCP sockets, the ones created
by the userspace (IPPROTO_MPTCP). This is useful for BPF hooks involving
these sockets, e.g. [gs]etsocktopt.

bpf_skc_to_mptcp_sock() uses bpf_mptcp_sock_from_subflow(). The former
suggests any MPTCP type/subtype can be used, but the latter only accepts
subflow ones. So bpf_mptcp_sock_from_subflow is modified here to support
MPTCP socket, and renamed to avoid confusions.

Signed-off-by: Geliang Tang <[email protected]>

Author: Geliang Tang

include/net/mptcp.h

@@ -322,9 +322,9 @@ static inline void mptcpv6_handle_mapped(struct sock *sk, bool mapped) { }
 #endif
 
 #if defined(CONFIG_MPTCP) && defined(CONFIG_BPF_SYSCALL)
-struct mptcp_sock *bpf_mptcp_sock_from_subflow(struct sock *sk);
+struct mptcp_sock *bpf_mptcp_sock_from_sock(struct sock *sk);
 #else
-static inline struct mptcp_sock *bpf_mptcp_sock_from_subflow(struct sock *sk) { return NULL; }
+static inline struct mptcp_sock *bpf_mptcp_sock_from_sock(struct sock *sk) { return NULL; }
 #endif
 
 #if !IS_ENABLED(CONFIG_MPTCP)

net/core/filter.c

@@ -11836,7 +11836,7 @@ const struct bpf_func_proto bpf_skc_to_unix_sock_proto = {
 BPF_CALL_1(bpf_skc_to_mptcp_sock, struct sock *, sk)
 {
 	BTF_TYPE_EMIT(struct mptcp_sock);
-	return (unsigned long)bpf_mptcp_sock_from_subflow(sk);
+	return (unsigned long)bpf_mptcp_sock_from_sock(sk);
 }
 
 const struct bpf_func_proto bpf_skc_to_mptcp_sock_proto = {

net/mptcp/bpf.c

@@ -188,9 +188,15 @@ static struct bpf_struct_ops bpf_mptcp_sched_ops = {
 };
 #endif /* CONFIG_BPF_JIT */
 
-struct mptcp_sock *bpf_mptcp_sock_from_subflow(struct sock *sk)
+struct mptcp_sock *bpf_mptcp_sock_from_sock(struct sock *sk)
 {
-	if (sk && sk_fullsock(sk) && sk->sk_protocol == IPPROTO_TCP && sk_is_mptcp(sk))
+	if (unlikely(!sk || !sk_fullsock(sk)))
+		return NULL;
+
+	if (sk->sk_protocol == IPPROTO_MPTCP)
+		return mptcp_sk(sk);
+
+	if (sk->sk_protocol == IPPROTO_TCP && sk_is_mptcp(sk))
 		return mptcp_sk(mptcp_subflow_ctx(sk)->conn);
 
 	return NULL;