[PATCH v2 bpf-next 6/8] bpf: mptcp: Don't support BPF_SOCK_OPS_RCVQ_CB_FLAG.

[Kuniyuki Iwashima <kuniyu@google.com>]

The next patch exposes a new kfunc calling __tcp_set_rcvlowat()
to bpf_tcp_ops.

MPTCP has its own sock->ops->set_rcvlowat() / mptcp_set_rcvlowat(),
so we should not allow calling __tcp_set_rcvlowat() on MPTCP
subflows.

Let's disable BPF_SOCK_OPS_RCVQ_CB_FLAG for MPTCP for now.

If needed in the future, bpf_tcp_ops_set_rcvlowat() could be
extended to properly support MPTCP.

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
---
 include/net/tcp.h      | 15 +++++++++++++++
 net/core/filter.c      | 10 ++++++----
 net/ipv4/bpf_tcp_ops.c |  5 ++++-
 3 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 07426e8641b7..d3cf655da9ec 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -2932,6 +2932,16 @@ static inline int tcp_call_bpf_3arg(struct sock *sk, int op, u32 arg1, u32 arg2,
 	return tcp_call_bpf(sk, op, 3, args);
 }
 
+static inline int tcp_set_sock_ops_cb_flags(struct sock *sk, int val)
+{
+	if (sk_is_mptcp(sk) &&
+	    (val & BPF_SOCK_OPS_RCVQ_CB_FLAG))
+		return -EOPNOTSUPP;
+
+	tcp_sk(sk)->bpf_sock_ops_cb_flags = val;
+	return 0;
+}
+
 static inline void tcp_clear_sock_ops_cb_flags(struct sock *sk)
 {
 	tcp_sk(sk)->bpf_sock_ops_cb_flags = 0;
@@ -2954,6 +2964,11 @@ static inline int tcp_call_bpf_3arg(struct sock *sk, int op, u32 arg1, u32 arg2,
 	return -EPERM;
 }
 
+static inline int tcp_set_sock_ops_cb_flags(struct sock *sk, int val)
+{
+	return -EOPNOTSUPP;
+}
+
 static inline void tcp_clear_sock_ops_cb_flags(struct sock *sk)
 {
 }
diff --git a/net/core/filter.c b/net/core/filter.c
index 5feb99884682..f29c061bb066 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -5588,8 +5588,7 @@ static int bpf_sol_tcp_setsockopt(struct sock *sk, int optname,
 	case TCP_BPF_SOCK_OPS_CB_FLAGS:
 		if (val & ~(BPF_SOCK_OPS_ALL_CB_FLAGS))
 			return -EINVAL;
-		tp->bpf_sock_ops_cb_flags = val;
-		break;
+		return tcp_set_sock_ops_cb_flags(sk, val);
 	default:
 		return -EINVAL;
 	}
@@ -6178,8 +6177,9 @@ static const struct bpf_func_proto bpf_sock_ops_getsockopt_proto = {
 BPF_CALL_2(bpf_sock_ops_cb_flags_set, struct bpf_sock_ops_kern *, bpf_sock,
 	   int, argval)
 {
-	struct sock *sk = bpf_sock->sk;
 	int val = argval & BPF_SOCK_OPS_ALL_CB_FLAGS;
+	struct sock *sk = bpf_sock->sk;
+	int err;
 
 	if (!is_locked_tcp_sock_ops(bpf_sock))
 		return -EOPNOTSUPP;
@@ -6187,7 +6187,9 @@ BPF_CALL_2(bpf_sock_ops_cb_flags_set, struct bpf_sock_ops_kern *, bpf_sock,
 	if (!IS_ENABLED(CONFIG_INET) || !sk_fullsock(sk))
 		return -EINVAL;
 
-	tcp_sk(sk)->bpf_sock_ops_cb_flags = val;
+	err = tcp_set_sock_ops_cb_flags(sk, val);
+	if (err)
+		return err;
 
 	return argval & (~BPF_SOCK_OPS_ALL_CB_FLAGS);
 }
diff --git a/net/ipv4/bpf_tcp_ops.c b/net/ipv4/bpf_tcp_ops.c
index 4b48711d92a2..b0cade34cce6 100644
--- a/net/ipv4/bpf_tcp_ops.c
+++ b/net/ipv4/bpf_tcp_ops.c
@@ -223,8 +223,11 @@ const struct bpf_func_proto bpf_tcp_ops_get_retval_proto = {
 BPF_CALL_2(bpf_tcp_ops_cb_flags_set, struct sock *, sk, int, argval)
 {
 	int val = argval & BPF_SOCK_OPS_ALL_CB_FLAGS;
+	int err;
 
-	tcp_sk(sk)->bpf_sock_ops_cb_flags = val;
+	err = tcp_set_sock_ops_cb_flags(sk, val);
+	if (err)
+		return err;
 
 	return argval & ~BPF_SOCK_OPS_ALL_CB_FLAGS;
 }
-- 
2.56.0.rc1.315.gc6ed9934b7-goog