mptcp: corner case locking for rx path fields initialization

Most MPTCP-level related fields are under the mptcp data lock
protection, but are written one-off without such lock at MPC
complete time, both for the client and the server

Leverage the mptcp_propagate_state() infrastructure to move such
initialization under the proper lock client-wise.

The server side critical init steps are done by
mptcp_subflow_fully_established(): ensure the caller properly held the
relevant lock, and avoid acquiring the same lock in the nested scopes.

There are no real potential races, as write access to such fields
is implicitly serialized by the MPTCP state machine; the primary
goal is consistency.

Fixes: d22f4988ffec ("mptcp: process MP_CAPABLE data option")
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 32 insertions, 24 deletions

diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index c2df34ebcf28..c34ecadee120 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -441,20 +441,6 @@ void __mptcp_sync_state(struct sock *sk, int state)
 	}
 }
 
-static void mptcp_propagate_state(struct sock *sk, struct sock *ssk)
-{
-	struct mptcp_sock *msk = mptcp_sk(sk);
-
-	mptcp_data_lock(sk);
-	if (!sock_owned_by_user(sk)) {
-		__mptcp_sync_state(sk, ssk->sk_state);
-	} else {
-		msk->pending_state = ssk->sk_state;
-		__set_bit(MPTCP_SYNC_STATE, &msk->cb_flags);
-	}
-	mptcp_data_unlock(sk);
-}
-
 static void subflow_set_remote_key(struct mptcp_sock *msk,
 				   struct mptcp_subflow_context *subflow,
 				   const struct mptcp_options_received *mp_opt)
@@ -476,6 +462,31 @@ static void subflow_set_remote_key(struct mptcp_sock *msk,
 	atomic64_set(&msk->rcv_wnd_sent, subflow->iasn);
 }
 
+static void mptcp_propagate_state(struct sock *sk, struct sock *ssk,
+				  struct mptcp_subflow_context *subflow,
+				  const struct mptcp_options_received *mp_opt)
+{
+	struct mptcp_sock *msk = mptcp_sk(sk);
+
+	mptcp_data_lock(sk);
+	if (mp_opt) {
+		/* Options are available only in the non fallback cases
+		 * avoid updating rx path fields otherwise
+		 */
+		WRITE_ONCE(msk->snd_una, subflow->idsn + 1);
+		WRITE_ONCE(msk->wnd_end, subflow->idsn + 1 + tcp_sk(ssk)->snd_wnd);
+		subflow_set_remote_key(msk, subflow, mp_opt);
+	}
+
+	if (!sock_owned_by_user(sk)) {
+		__mptcp_sync_state(sk, ssk->sk_state);
+	} else {
+		msk->pending_state = ssk->sk_state;
+		__set_bit(MPTCP_SYNC_STATE, &msk->cb_flags);
+	}
+	mptcp_data_unlock(sk);
+}
+
 static void subflow_finish_connect(struct sock *sk, const struct sk_buff *skb)
 {
 	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
@@ -510,10 +521,9 @@ static void subflow_finish_connect(struct sock *sk, const struct sk_buff *skb)
 		if (mp_opt.deny_join_id0)
 			WRITE_ONCE(msk->pm.remote_deny_join_id0, true);
 		subflow->mp_capable = 1;
-		subflow_set_remote_key(msk, subflow, &mp_opt);
 		MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_MPCAPABLEACTIVEACK);
 		mptcp_finish_connect(sk);
-		mptcp_propagate_state(parent, sk);
+		mptcp_propagate_state(parent, sk, subflow, &mp_opt);
 	} else if (subflow->request_join) {
 		u8 hmac[SHA256_DIGEST_SIZE];
 
@@ -556,7 +566,7 @@ static void subflow_finish_connect(struct sock *sk, const struct sk_buff *skb)
 		}
 	} else if (mptcp_check_fallback(sk)) {
 fallback:
-		mptcp_propagate_state(parent, sk);
+		mptcp_propagate_state(parent, sk, subflow, NULL);
 	}
 	return;
 
@@ -741,17 +751,16 @@ void mptcp_subflow_drop_ctx(struct sock *ssk)
 	kfree_rcu(ctx, rcu);
 }
 
-void mptcp_subflow_fully_established(struct mptcp_subflow_context *subflow,
-				     const struct mptcp_options_received *mp_opt)
+void __mptcp_subflow_fully_established(struct mptcp_sock *msk,
+				       struct mptcp_subflow_context *subflow,
+				       const struct mptcp_options_received *mp_opt)
 {
-	struct mptcp_sock *msk = mptcp_sk(subflow->conn);
-
 	subflow_set_remote_key(msk, subflow, mp_opt);
 	subflow->fully_established = 1;
 	WRITE_ONCE(msk->fully_established, true);
 
 	if (subflow->is_mptfo)
-		mptcp_fastopen_gen_msk_ackseq(msk, subflow, mp_opt);
+		__mptcp_fastopen_gen_msk_ackseq(msk, subflow, mp_opt);
 }
 
 static struct sock *subflow_syn_recv_sock(const struct sock *sk,
@@ -844,7 +853,6 @@ create_child:
 			 * mpc option
 			 */
 			if (mp_opt.suboptions & OPTION_MPTCP_MPC_ACK) {
-				mptcp_subflow_fully_established(ctx, &mp_opt);
 				mptcp_pm_fully_established(owner, child);
 				ctx->pm_notified = 1;
 			}
@@ -1756,7 +1764,7 @@ static void subflow_state_change(struct sock *sk)
 		mptcp_do_fallback(sk);
 		pr_fallback(msk);
 		subflow->conn_finished = 1;
-		mptcp_propagate_state(parent, sk);
+		mptcp_propagate_state(parent, sk, subflow, NULL);
 	}
 
 	/* as recvmsg() does not acquire the subflow socket for ssk selection