diff mbox series

[net-next,9/9] subflow: introduce and use mptcp_can_accept_new_subflow()

Message ID 721ab4f59d741086b68bf20504805be785d72648.1594401165.git.pabeni@redhat.com
State Accepted, archived
Delegated to: Matthieu Baerts
Headers show
Series mptcp: cope better with mp_join storm | expand

Commit Message

Paolo Abeni July 10, 2020, 5:22 p.m. UTC 
So that we can easily perform some basic PM-related
adimission checks before creating the child socket.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
---
Note: I initially used mptcp_can_accept_new_subflow() in
subflow_token_join_request(), too. The goal was add a follow-up
patch sending reset at rsk creation time in case of !can_accept
but I dismissed such patch because it feel "insecure"/potentially
dos prone send this early reset: an attacker could force an mptcp
server to send reset packets towards arbitrary IP/ports.

Additionally, after a quick look at mptcp.org, I could not find
trace of such early reset - looks like resets for bad MP_JOINs
are send only at syn_recv_sock() time.
---
 net/mptcp/subflow.c | 7 +++++++
 1 file changed, 7 insertions(+)
diff mbox series

Patch

diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index 1ea37c776777..07c6b3a65bb6 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -53,6 +53,12 @@  static void subflow_generate_hmac(u64 key1, u64 key2, u32 nonce1, u32 nonce2,
 	mptcp_crypto_hmac_sha(key1, key2, msg, 8, hmac);
 }
 
+static bool mptcp_can_accept_new_subflow(const struct mptcp_sock *msk)
+{
+	return inet_sk_state_load((struct sock *)msk) == TCP_ESTABLISHED &&
+	       READ_ONCE(msk->pm.accept_subflow);
+}
+
 /* validate received token and create truncated hmac and nonce for SYN-ACK */
 static struct mptcp_sock *subflow_token_join_request(struct request_sock *req,
 						     const struct sk_buff *skb)
@@ -445,6 +451,7 @@  static struct sock *subflow_syn_recv_sock(const struct sock *sk,
 	} else if (subflow_req->mp_join) {
 		mptcp_get_options(skb, &mp_opt);
 		if (!mp_opt.mp_join ||
+		    !mptcp_can_accept_new_subflow(subflow_req->msk) ||
 		    !subflow_hmac_valid(req, &mp_opt)) {
 			SUBFLOW_REQ_INC_STATS(req, MPTCP_MIB_JOINACKMAC);
 			fallback = true;