Merge branch 'sctp-avoid-redundant-initialisation-in-sctp_accept-and-sctp_do_peeloff'

Kuniyuki Iwashima says:

====================
sctp: Avoid redundant initialisation in sctp_accept() and sctp_do_peeloff().

When sctp_accept() and sctp_do_peeloff() allocates a new socket,
somehow sk_alloc() is used, and the new socket goes through full
initialisation, but most of the fields are overwritten later.

  1)
  sctp_accept()
  |- sctp_v[46]_create_accept_sk()
  |  |- sk_alloc()
  |  |- sock_init_data()
  |  |- sctp_copy_sock()
  |  `- newsk->sk_prot->init() / sctp_init_sock()
  |
  `- sctp_sock_migrate()
     `- sctp_copy_descendant(newsk, oldsk)

  sock_init_data() initialises struct sock, but many fields are
  overwritten by sctp_copy_sock(), which inherits fields of struct
  sock and inet_sock from the parent socket.

  sctp_init_sock() fully initialises struct sctp_sock, but later
  sctp_copy_descendant() inherits most fields from the parent's
  struct sctp_sock by memcpy().

  2)
  sctp_do_peeloff()
  |- sock_create()
  |  |
  |  ...
  |      |- sk_alloc()
  |      |- sock_init_data()
  |  ...
  |    `- newsk->sk_prot->init() / sctp_init_sock()
  |
  |- sctp_copy_sock()
  `- sctp_sock_migrate()
     `- sctp_copy_descendant(newsk, oldsk)

  sock_create() creates a brand new socket, but sctp_copy_sock()
  and sctp_sock_migrate() overwrite most of the fields.

So, sk_alloc(), sock_init_data(), sctp_copy_sock(), and
sctp_copy_descendant() can be replaced with a single function
like sk_clone_lock().

This series does the conversion and removes TODO comment added
by commit 4a997d49d92ad ("tcp: Save lock_sock() for memcg in
inet_csk_accept().").

Tested accept() and SCTP_SOCKOPT_PEELOFF and both work properly.

  socket(AF_INET, SOCK_STREAM, IPPROTO_SCTP) = 3
  bind(3, {sa_family=AF_INET, sin_port=htons(0), sin_addr=inet_addr("127.0.0.1")}, 16) = 0
  listen(3, -1)                           = 0
  getsockname(3, {sa_family=AF_INET, sin_port=htons(49460), sin_addr=inet_addr("127.0.0.1")}, [16]) = 0
  socket(AF_INET, SOCK_STREAM, IPPROTO_SCTP) = 4
  connect(4, {sa_family=AF_INET, sin_port=htons(49460), sin_addr=inet_addr("127.0.0.1")}, 16) = 0
  accept(3, NULL, NULL)                   = 5
  ...
  socket(AF_INET, SOCK_SEQPACKET, IPPROTO_SCTP) = 3
  bind(3, {sa_family=AF_INET, sin_port=htons(0), sin_addr=inet_addr("127.0.0.1")}, 16) = 0
  listen(3, -1)                           = 0
  getsockname(3, {sa_family=AF_INET, sin_port=htons(48240), sin_addr=inet_addr("127.0.0.1")}, [16]) = 0
  socket(AF_INET, SOCK_SEQPACKET, IPPROTO_SCTP) = 4
  connect(4, {sa_family=AF_INET, sin_port=htons(48240), sin_addr=inet_addr("127.0.0.1")}, 16) = 0
  getsockopt(3, SOL_SCTP, SCTP_SOCKOPT_PEELOFF, "*\0\0\0\5\0\0\0", [8]) = 5

v1: https://lore.kernel.org/20251021214422.1941691-1-kuniyu@google.com
====================

Link: https://patch.msgid.link/20251023231751.4168390-1-kuniyu@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

4 files changed, 7 insertions, 14 deletions

diff --git a/include/net/inet_sock.h b/include/net/inet_sock.h
index b6ec08072533..ac1c75975908 100644
--- a/include/net/inet_sock.h
+++ b/include/net/inet_sock.h
@@ -355,14 +355,6 @@ static inline struct sock *skb_to_full_sk(const struct sk_buff *skb)
 
 #define inet_sk(ptr) container_of_const(ptr, struct inet_sock, sk)
 
-static inline void __inet_sk_copy_descendant(struct sock *sk_to,
-					     const struct sock *sk_from,
-					     const int ancestor_size)
-{
-	memcpy(inet_sk(sk_to) + 1, inet_sk(sk_from) + 1,
-	       sk_from->sk_prot->obj_size - ancestor_size);
-}
-
 int inet_sk_rebuild_header(struct sock *sk);
 
 /**
diff --git a/include/net/sctp/sctp.h b/include/net/sctp/sctp.h
index e96d1bd087f6..bb4b80c12541 100644
--- a/include/net/sctp/sctp.h
+++ b/include/net/sctp/sctp.h
@@ -94,8 +94,7 @@ void sctp_data_ready(struct sock *sk);
 __poll_t sctp_poll(struct file *file, struct socket *sock,
 		poll_table *wait);
 void sctp_sock_rfree(struct sk_buff *skb);
-void sctp_copy_sock(struct sock *newsk, struct sock *sk,
-		    struct sctp_association *asoc);
+
 extern struct percpu_counter sctp_sockets_allocated;
 int sctp_asconf_mgmt(struct sctp_sock *, struct sctp_sockaddr_entry *);
 struct sk_buff *sctp_skb_recv_datagram(struct sock *, int, int *);
diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
index 2ae390219efd..3dd304e411d0 100644
--- a/include/net/sctp/structs.h
+++ b/include/net/sctp/structs.h
@@ -497,9 +497,6 @@ struct sctp_pf {
 	int  (*bind_verify) (struct sctp_sock *, union sctp_addr *);
 	int  (*send_verify) (struct sctp_sock *, union sctp_addr *);
 	int  (*supported_addrs)(const struct sctp_sock *, __be16 *);
-	struct sock *(*create_accept_sk) (struct sock *sk,
-					  struct sctp_association *asoc,
-					  bool kern);
 	int (*addr_to_user)(struct sctp_sock *sk, union sctp_addr *addr);
 	void (*to_sk_saddr)(union sctp_addr *, struct sock *sk);
 	void (*to_sk_daddr)(union sctp_addr *, struct sock *sk);
diff --git a/include/net/sock.h b/include/net/sock.h
index 01ce231603db..c7e58b8e8a90 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1822,7 +1822,12 @@ struct sock *sk_alloc(struct net *net, int family, gfp_t priority,
 void sk_free(struct sock *sk);
 void sk_net_refcnt_upgrade(struct sock *sk);
 void sk_destruct(struct sock *sk);
-struct sock *sk_clone_lock(const struct sock *sk, const gfp_t priority);
+struct sock *sk_clone(const struct sock *sk, const gfp_t priority, bool lock);
+
+static inline struct sock *sk_clone_lock(const struct sock *sk, const gfp_t priority)
+{
+	return sk_clone(sk, priority, true);
+}
 
 struct sk_buff *sock_wmalloc(struct sock *sk, unsigned long size, int force,
 			     gfp_t priority);