sctp: Don't call sk->sk_prot->init() in sctp_v[46]_create_accept_sk().

sctp_accept() calls sctp_v[46]_create_accept_sk() to allocate a new
socket and calls sctp_sock_migrate() to copy fields from the parent
socket to the new socket.

sctp_v[46]_create_accept_sk() calls sctp_init_sock() to initialise
sctp_sock, but most fields are overwritten by sctp_copy_descendant()
called from sctp_sock_migrate().

Things done in sctp_init_sock() but not in sctp_sock_migrate() are
the following:

  1. Copy sk->sk_gso
  2. Copy sk->sk_destruct (sctp_v6_init_sock())
  3. Allocate sctp_sock.ep
  4. Initialise sctp_sock.pd_lobby
  5. Count sk_sockets_allocated_inc(), sock_prot_inuse_add(),
     and SCTP_DBG_OBJCNT_INC()

Let's do these in sctp_copy_sock() and sctp_sock_migrate() and avoid
calling sk->sk_prot->init() in sctp_v[46]_create_accept_sk().

Note that sk->sk_destruct is already copied in sctp_copy_sock().

Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
Acked-by: Xin Long <lucien.xin@gmail.com>
Link: https://patch.msgid.link/20251023231751.4168390-4-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/sctp/ipv6.c

@@ -789,7 +789,7 @@ static struct sock *sctp_v6_create_accept_sk(struct sock *sk,
 
 	newsk = sk_alloc(sock_net(sk), PF_INET6, GFP_KERNEL, sk->sk_prot, kern);
 	if (!newsk)
-		goto out;
+		return NULL;
 
 	sock_init_data(NULL, newsk);
 
@@ -818,12 +818,6 @@ static struct sock *sctp_v6_create_accept_sk(struct sock *sk,
 
 	newsk->sk_v6_rcv_saddr = sk->sk_v6_rcv_saddr;
 
-	if (newsk->sk_prot->init(newsk)) {
-		sk_common_release(newsk);
-		newsk = NULL;
-	}
-
-out:
 	return newsk;
 }
 

net/sctp/protocol.c

@@ -590,7 +590,7 @@ static struct sock *sctp_v4_create_accept_sk(struct sock *sk,
 	struct inet_sock *newinet;
 
 	if (!newsk)
-		goto out;
+		return NULL;
 
 	sock_init_data(NULL, newsk);
 
@@ -603,12 +603,6 @@ static struct sock *sctp_v4_create_accept_sk(struct sock *sk,
 
 	newinet->inet_daddr = asoc->peer.primary_addr.v4.sin_addr.s_addr;
 
-	if (newsk->sk_prot->init(newsk)) {
-		sk_common_release(newsk);
-		newsk = NULL;
-	}
-
-out:
 	return newsk;
 }
 

net/sctp/socket.c

@@ -4851,7 +4851,7 @@ static int sctp_disconnect(struct sock *sk, int flags)
  */
 static struct sock *sctp_accept(struct sock *sk, struct proto_accept_arg *arg)
 {
-	struct sctp_sock *sp;
+	struct sctp_sock *sp, *newsp;
 	struct sctp_endpoint *ep;
 	struct sock *newsk = NULL;
 	struct sctp_association *asoc;
@@ -4891,19 +4891,35 @@ static struct sock *sctp_accept(struct sock *sk, struct proto_accept_arg *arg)
 		goto out;
 	}
 
+	newsp = sctp_sk(newsk);
+	newsp->ep = sctp_endpoint_new(newsk, GFP_KERNEL);
+	if (!newsp->ep) {
+		error = -ENOMEM;
+		goto out_release;
+	}
+
+	skb_queue_head_init(&newsp->pd_lobby);
+
+	sk_sockets_allocated_inc(newsk);
+	sock_prot_inuse_add(sock_net(sk), newsk->sk_prot, 1);
+	SCTP_DBG_OBJCNT_INC(sock);
+
 	/* Populate the fields of the newsk from the oldsk and migrate the
 	 * asoc to the newsk.
 	 */
 	error = sctp_sock_migrate(sk, newsk, asoc, SCTP_SOCKET_TCP);
-	if (error) {
+	if (error)
-		sk_common_release(newsk);
+		goto out_release;
-		newsk = NULL;
-	}
 
 out:
 	release_sock(sk);
 	arg->err = error;
 	return newsk;
+
+out_release:
+	sk_common_release(newsk);
+	newsk = NULL;
+	goto out;
 }
 
 /* The SCTP ioctl handler. */
@@ -9469,6 +9485,7 @@ void sctp_copy_sock(struct sock *newsk, struct sock *sk,
 	newsk->sk_rcvtimeo = READ_ONCE(sk->sk_rcvtimeo);
 	newsk->sk_sndtimeo = READ_ONCE(sk->sk_sndtimeo);
 	newsk->sk_rxhash = sk->sk_rxhash;
+	newsk->sk_gso_type = sk->sk_gso_type;
 
 	newinet = inet_sk(newsk);