From: Geliang Tang <tanggeliang@kylinos.cn>

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 <tanggeliang@kylinos.cn>
Reviewed-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
Notes:
 - v2: new patch.
---
 include/net/mptcp.h |  4 ++--
 net/core/filter.c   |  2 +-
 net/mptcp/bpf.c     | 10 ++++++++--
 3 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/include/net/mptcp.h b/include/net/mptcp.h
index 814b5f2e3ed5e3e474a2bac5e4cca5a89abcfe1c..94d5976f7b8d8eb8b82f298f7b33ecd653937dc0 100644
--- a/include/net/mptcp.h
+++ b/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)
diff --git a/net/core/filter.c b/net/core/filter.c
index 6625b3f563a4a3110a76b9c12a46340828e16b6e..40ed3854a899bf9d11847ec0e8aee174923f03d2 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -11833,7 +11833,7 @@ 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 = {
diff --git a/net/mptcp/bpf.c b/net/mptcp/bpf.c
index 8a16672b94e2384f5263e1432296cbca1236bb30..988b22a06331ac293b36f3c6f9bc29ff0f6db048 100644
--- a/net/mptcp/bpf.c
+++ b/net/mptcp/bpf.c
@@ -12,9 +12,15 @@
 #include <linux/bpf.h>
 #include "protocol.h"
 
-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;

-- 
2.47.1