[PATCH ipsec v2] xfrm: espintcp: reorder operations within espintcp_init_sk

[Sabrina Dubroca <sd@queasysnail.net>]

When enabled on a socket, espintcp sets the socket callbacks to its
own before it has finished setting up its context and published it as
icsk_ulp_data. Any one of those callbacks that gets called before will
dereference a NULL icsk_ulp_data.

Fix this by reording the operations, and add memory barriers to ensure
callers will have a struct espintcp_ctx available. Add a few
WRITE_ONCE/READ_ONCE too while we're there.

Fixes: e27cca96cd68 ("xfrm: add espintcp (RFC 8229)")
Cc: stable@vger.kernel.org
Reported-by: Yuan Tan <yuantan098@gmail.com>
Reported-by: Yifan Wu <yifanwucs@gmail.com>
Reported-by: Juefei Pu <tomapufckgml@gmail.com>
Reported-by: Xin Liu <bird@lzu.edu.cn>
Reported-by: Peihan Liu <ronbogo@outlook.com>
Reported-by: Yilin Zhu <zylzyl2333@gmail.com>
Reported-by: Ren Wei <n05ec@lzu.edu.cn>
Reported-by: Eulgyu Kim <eulgyukim@snu.ac.kr>
Reported-by: Jaeyoung Chung <jjy600901@snu.ac.kr>
Link: https://lore.kernel.org/all/c30b645074a1b379e0f7fe297f917c66137d9964.1778464688.git.zylzyl2333@gmail.com/
Link: https://lore.kernel.org/all/20260819155349.3555804-1-jjy600901@snu.ac.kr
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
---
v2: more barriers and READ/WRITE once according to the ai review
v1: https://lore.kernel.org/all/dcb164e6a1064fcd32c2e72fd9ee918dd1427f15.1790617484.git.sd@queasysnail.net/

 include/net/espintcp.h |  5 +++--
 net/xfrm/espintcp.c    | 43 +++++++++++++++++++++++++-----------------
 2 files changed, 29 insertions(+), 19 deletions(-)

diff --git a/include/net/espintcp.h b/include/net/espintcp.h
index c70efd704b6d..7cad3c6822df 100644
--- a/include/net/espintcp.h
+++ b/include/net/espintcp.h
@@ -34,7 +34,8 @@ static inline struct espintcp_ctx *espintcp_getctx(const struct sock *sk)
 {
 	const struct inet_connection_sock *icsk = inet_csk(sk);
 
-	/* RCU is only needed for diag */
-	return (__force void *)icsk->icsk_ulp_data;
+	/* pairs with smp_wmb() in espintcp_init_sk() */
+	smp_rmb();
+	return (__force void *)READ_ONCE(icsk->icsk_ulp_data);
 }
 #endif
diff --git a/net/xfrm/espintcp.c b/net/xfrm/espintcp.c
index 3e72b9f067b9..4052ae5bbb2e 100644
--- a/net/xfrm/espintcp.c
+++ b/net/xfrm/espintcp.c
@@ -434,7 +434,9 @@ static void espintcp_destruct(struct sock *sk)
 
 bool tcp_is_ulp_esp(struct sock *sk)
 {
-	return sk->sk_prot == &espintcp_prot || sk->sk_prot == &espintcp6_prot;
+	const struct proto *prot = READ_ONCE(sk->sk_prot);
+
+	return prot == &espintcp_prot || prot == &espintcp6_prot;
 }
 EXPORT_SYMBOL_GPL(tcp_is_ulp_esp);
 
@@ -466,34 +468,41 @@ static int espintcp_init_sk(struct sock *sk)
 
 	__sk_dst_reset(sk);
 
-	strp_check_rcv(&ctx->strp);
 	skb_queue_head_init(&ctx->ike_queue);
 	skb_queue_head_init(&ctx->out_queue);
+	INIT_WORK(&ctx->work, espintcp_tx_work);
+
+	ctx->saved_data_ready = sk->sk_data_ready;
+	ctx->saved_write_space = sk->sk_write_space;
+	ctx->saved_destruct = sk->sk_destruct;
+
+	/* avoid using task_frag */
+	sk->sk_allocation = GFP_ATOMIC;
+	sk->sk_use_task_frag = false;
+
+	rcu_assign_pointer(icsk->icsk_ulp_data, ctx);
+
+	/* pairs with smp_rmb() in espintcp_getctx() */
+	smp_wmb();
+
+	WRITE_ONCE(sk->sk_data_ready, espintcp_data_ready);
+	WRITE_ONCE(sk->sk_write_space, espintcp_write_space);
+	sk->sk_destruct = espintcp_destruct;
 
 	if (sk->sk_family == AF_INET) {
-		sk->sk_prot = &espintcp_prot;
-		sk->sk_socket->ops = &espintcp_ops;
+		WRITE_ONCE(sk->sk_prot, &espintcp_prot);
+		WRITE_ONCE(sk->sk_socket->ops, &espintcp_ops);
 	} else {
 		mutex_lock(&tcpv6_prot_mutex);
 		if (!espintcp6_prot.recvmsg)
 			build_protos(&espintcp6_prot, &espintcp6_ops, sk->sk_prot, sk->sk_socket->ops);
 		mutex_unlock(&tcpv6_prot_mutex);
 
-		sk->sk_prot = &espintcp6_prot;
-		sk->sk_socket->ops = &espintcp6_ops;
+		WRITE_ONCE(sk->sk_prot, &espintcp6_prot);
+		WRITE_ONCE(sk->sk_socket->ops, &espintcp6_ops);
 	}
-	ctx->saved_data_ready = sk->sk_data_ready;
-	ctx->saved_write_space = sk->sk_write_space;
-	ctx->saved_destruct = sk->sk_destruct;
-	sk->sk_data_ready = espintcp_data_ready;
-	sk->sk_write_space = espintcp_write_space;
-	sk->sk_destruct = espintcp_destruct;
-	rcu_assign_pointer(icsk->icsk_ulp_data, ctx);
-	INIT_WORK(&ctx->work, espintcp_tx_work);
 
-	/* avoid using task_frag */
-	sk->sk_allocation = GFP_ATOMIC;
-	sk->sk_use_task_frag = false;
+	strp_check_rcv(&ctx->strp);
 
 	return 0;
 
-- 
2.55.0