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Subject[PATCH net-next v2 2/4] mptcp: simplify subflow_syn_recv_sock()
From: Paolo Abeni <pabeni@redhat.com>

Postpone the msk cloning to the child process creation
so that we can avoid a bunch of conditionals.

Link: https://github.com/multipath-tcp/mptcp_net-next/issues/61
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
---
net/mptcp/subflow.c | 41 +++++++++++++----------------------------
1 file changed, 13 insertions(+), 28 deletions(-)

diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index a11f4c525e01..33dd27765116 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -696,14 +696,6 @@ static bool subflow_hmac_valid(const struct request_sock *req,
return !crypto_memneq(hmac, mp_opt->hmac, MPTCPOPT_HMAC_LEN);
}

-static void mptcp_force_close(struct sock *sk)
-{
- /* the msk is not yet exposed to user-space, and refcount is 2 */
- inet_sk_state_store(sk, TCP_CLOSE);
- sk_common_release(sk);
- sock_put(sk);
-}
-
static void subflow_ulp_fallback(struct sock *sk,
struct mptcp_subflow_context *old_ctx)
{
@@ -755,7 +747,6 @@ static struct sock *subflow_syn_recv_sock(const struct sock *sk,
struct mptcp_subflow_request_sock *subflow_req;
struct mptcp_options_received mp_opt;
bool fallback, fallback_is_fatal;
- struct sock *new_msk = NULL;
struct mptcp_sock *owner;
struct sock *child;

@@ -784,14 +775,9 @@ static struct sock *subflow_syn_recv_sock(const struct sock *sk,
* options.
*/
mptcp_get_options(skb, &mp_opt);
- if (!(mp_opt.suboptions & OPTIONS_MPTCP_MPC)) {
+ if (!(mp_opt.suboptions & OPTIONS_MPTCP_MPC))
fallback = true;
- goto create_child;
- }

- new_msk = mptcp_sk_clone(listener->conn, &mp_opt, req);
- if (!new_msk)
- fallback = true;
} else if (subflow_req->mp_join) {
mptcp_get_options(skb, &mp_opt);
if (!(mp_opt.suboptions & OPTIONS_MPTCP_MPJ) ||
@@ -820,21 +806,23 @@ static struct sock *subflow_syn_recv_sock(const struct sock *sk,
subflow_add_reset_reason(skb, MPTCP_RST_EMPTCP);
goto dispose_child;
}
-
- mptcp_subflow_drop_ctx(child);
- goto out;
+ goto fallback;
}

/* ssk inherits options of listener sk */
ctx->setsockopt_seq = listener->setsockopt_seq;

if (ctx->mp_capable) {
- owner = mptcp_sk(new_msk);
+ ctx->conn = mptcp_sk_clone(listener->conn, &mp_opt, req);
+ if (!ctx->conn)
+ goto fallback;
+
+ owner = mptcp_sk(ctx->conn);

/* this can't race with mptcp_close(), as the msk is
* not yet exposted to user-space
*/
- inet_sk_state_store((void *)new_msk, TCP_ESTABLISHED);
+ inet_sk_state_store(ctx->conn, TCP_ESTABLISHED);

/* record the newly created socket as the first msk
* subflow, but don't link it yet into conn_list
@@ -844,11 +832,9 @@ static struct sock *subflow_syn_recv_sock(const struct sock *sk,
/* new mpc subflow takes ownership of the newly
* created mptcp socket
*/
- mptcp_sk(new_msk)->setsockopt_seq = ctx->setsockopt_seq;
+ owner->setsockopt_seq = ctx->setsockopt_seq;
mptcp_pm_new_connection(owner, child, 1);
mptcp_token_accept(subflow_req, owner);
- ctx->conn = new_msk;
- new_msk = NULL;

/* set msk addresses early to ensure mptcp_pm_get_local_id()
* uses the correct data
@@ -898,11 +884,6 @@ static struct sock *subflow_syn_recv_sock(const struct sock *sk,
}
}

-out:
- /* dispose of the left over mptcp master, if any */
- if (unlikely(new_msk))
- mptcp_force_close(new_msk);
-
/* check for expected invariant - should never trigger, just help
* catching eariler subtle bugs
*/
@@ -920,6 +901,10 @@ static struct sock *subflow_syn_recv_sock(const struct sock *sk,

/* The last child reference will be released by the caller */
return child;
+
+fallback:
+ mptcp_subflow_drop_ctx(child);
+ return child;
}

static struct inet_connection_sock_af_ops subflow_specific __ro_after_init;
--
2.39.2

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