[PATCH mptcp-next 2/5] mptcp: reject sockopt requiring ssks' lock in BPF context

[Gang Yan <gang.yan@linux.dev>]

From: Gang Yan <yangang@kylinos.cn>

Several MPTCP setsockopt handlers need to acquire the subflow lock
via lock_sock(ssk) to propagate settings to each subflow.  This lock
can sleep and is therefore not usable in BPF context where sleeping
is forbidden.

The short-term solution is to make any sockopt operation that requires
subflow-level lock fail with -EOPNOTSUPP when called from BPF context.

Signed-off-by: Gang Yan <yangang@kylinos.cn>
---
 net/mptcp/sockopt.c | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/net/mptcp/sockopt.c b/net/mptcp/sockopt.c
index 342aec7f9086..0c391247eb4c 100644
--- a/net/mptcp/sockopt.c
+++ b/net/mptcp/sockopt.c
@@ -185,6 +185,9 @@ static int mptcp_setsockopt_sol_socket_int(struct mptcp_sock *msk, int optname,
 	if (ret)
 		return ret;
 
+	if (has_current_bpf_ctx())
+		return -EOPNOTSUPP;
+
 	switch (optname) {
 	case SO_KEEPALIVE:
 	case SO_DEBUG:
@@ -218,6 +221,9 @@ static int mptcp_setsockopt_sol_socket_timestamping(struct mptcp_sock *msk,
 	struct so_timestamping timestamping;
 	int ret;
 
+	if (has_current_bpf_ctx())
+		return -EOPNOTSUPP;
+
 	if (optlen == sizeof(timestamping)) {
 		if (copy_from_sockptr(&timestamping, optval,
 				      sizeof(timestamping)))
@@ -265,6 +271,9 @@ static int mptcp_setsockopt_sol_socket_linger(struct mptcp_sock *msk, sockptr_t
 	sockptr_t kopt;
 	int ret;
 
+	if (has_current_bpf_ctx())
+		return -EOPNOTSUPP;
+
 	if (optlen < sizeof(ling))
 		return -EINVAL;
 
@@ -598,6 +607,9 @@ static int mptcp_setsockopt_sol_tcp_congestion(struct mptcp_sock *msk, sockptr_t
 	bool cap_net_admin;
 	int ret;
 
+	if (has_current_bpf_ctx())
+		return -EOPNOTSUPP;
+
 	if (optlen < 1)
 		return -EINVAL;
 
@@ -639,6 +651,9 @@ static int __mptcp_setsockopt_set_val(struct mptcp_sock *msk, int max,
 	struct mptcp_subflow_context *subflow;
 	int err = 0;
 
+	if (has_current_bpf_ctx())
+		return -EOPNOTSUPP;
+
 	mptcp_for_each_subflow(msk, subflow) {
 		struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
 		int ret;
@@ -662,6 +677,9 @@ static int __mptcp_setsockopt_sol_tcp_cork(struct mptcp_sock *msk, int val)
 	struct mptcp_subflow_context *subflow;
 	struct sock *sk = (struct sock *)msk;
 
+	if (has_current_bpf_ctx())
+		return -EOPNOTSUPP;
+
 	sockopt_seq_inc(msk);
 	msk->cork = !!val;
 	mptcp_for_each_subflow(msk, subflow) {
@@ -682,6 +700,9 @@ static int __mptcp_setsockopt_sol_tcp_nodelay(struct mptcp_sock *msk, int val)
 	struct mptcp_subflow_context *subflow;
 	struct sock *sk = (struct sock *)msk;
 
+	if (has_current_bpf_ctx())
+		return -EOPNOTSUPP;
+
 	sockopt_seq_inc(msk);
 	msk->nodelay = !!val;
 	mptcp_for_each_subflow(msk, subflow) {
@@ -749,6 +770,9 @@ static int mptcp_setsockopt_v4_set_tos(struct mptcp_sock *msk, int optname,
 	struct sock *sk = (struct sock *)msk;
 	int err, val;
 
+	if (has_current_bpf_ctx())
+		return -EOPNOTSUPP;
+
 	err = ip_setsockopt(sk, SOL_IP, optname, optval, optlen);
 
 	if (err != 0)
@@ -1654,6 +1678,9 @@ int mptcp_set_rcvlowat(struct sock *sk, int val)
 	if (space <= sk->sk_rcvbuf)
 		return 0;
 
+	if (has_current_bpf_ctx())
+		return -EOPNOTSUPP;
+
 	/* propagate the rcvbuf changes to all the subflows */
 	WRITE_ONCE(sk->sk_rcvbuf, space);
 	mptcp_for_each_subflow(mptcp_sk(sk), subflow) {
-- 
2.43.0