netdev - [PATCH net-next 3/3] net/tls: Annotate access to sk_prot with READ_ONCE/WRITE

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Date:   Tue, 17 Mar 2020 18:04:39 +0100
From:   Jakub Sitnicki <jakub@...udflare.com>
To:     netdev@...r.kernel.org
Cc:     kernel-team@...udflare.com,
        John Fastabend <john.fastabend@...il.com>
Subject: [PATCH net-next 3/3] net/tls: Annotate access to sk_prot with READ_ONCE/WRITE_ONCE

sockmap performs lockless writes to sk->sk_prot on the following paths:

tcp_bpf_{recvmsg|sendmsg} / sock_map_unref
  sk_psock_put
    sk_psock_drop
      sk_psock_restore_proto
        WRITE_ONCE(sk->sk_prot, proto)

To prevent load/store tearing [1], and to make tooling aware of intentional
shared access [2], we need to annotate other sites that access sk_prot with
READ_ONCE/WRITE_ONCE macros.

Change done with Coccinelle with following semantic patch:

@@
expression E;
identifier I;
struct sock *sk;
identifier sk_prot =~ "^sk_prot$";
@@
(
 E =
-sk->sk_prot
+READ_ONCE(sk->sk_prot)
|
-sk->sk_prot = E
+WRITE_ONCE(sk->sk_prot, E)
|
-sk->sk_prot
+READ_ONCE(sk->sk_prot)
 ->I
)

Signed-off-by: Jakub Sitnicki <jakub@...udflare.com>
---
 net/tls/tls_device.c | 2 +-
 net/tls/tls_main.c   | 9 +++++----
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/net/tls/tls_device.c b/net/tls/tls_device.c
index 1c5574e2e058..a562ebaaa33c 100644
--- a/net/tls/tls_device.c
+++ b/net/tls/tls_device.c
@@ -366,7 +366,7 @@ static int tls_do_allocation(struct sock *sk,
 	if (!offload_ctx->open_record) {
 		if (unlikely(!skb_page_frag_refill(prepend_size, pfrag,
 						   sk->sk_allocation))) {
-			sk->sk_prot->enter_memory_pressure(sk);
+			READ_ONCE(sk->sk_prot)->enter_memory_pressure(sk);
 			sk_stream_moderate_sndbuf(sk);
 			return -ENOMEM;
 		}
diff --git a/net/tls/tls_main.c b/net/tls/tls_main.c
index e7de0306a7df..156efce50dbd 100644
--- a/net/tls/tls_main.c
+++ b/net/tls/tls_main.c
@@ -69,7 +69,8 @@ void update_sk_prot(struct sock *sk, struct tls_context *ctx)
 {
 	int ip_ver = sk->sk_family == AF_INET6 ? TLSV6 : TLSV4;
 
-	sk->sk_prot = &tls_prots[ip_ver][ctx->tx_conf][ctx->rx_conf];
+	WRITE_ONCE(sk->sk_prot,
+		   &tls_prots[ip_ver][ctx->tx_conf][ctx->rx_conf]);
 }
 
 int wait_on_pending_writer(struct sock *sk, long *timeo)
@@ -312,7 +313,7 @@ static void tls_sk_proto_close(struct sock *sk, long timeout)
 	write_lock_bh(&sk->sk_callback_lock);
 	if (free_ctx)
 		rcu_assign_pointer(icsk->icsk_ulp_data, NULL);
-	sk->sk_prot = ctx->sk_proto;
+	WRITE_ONCE(sk->sk_prot, ctx->sk_proto);
 	if (sk->sk_write_space == tls_write_space)
 		sk->sk_write_space = ctx->sk_write_space;
 	write_unlock_bh(&sk->sk_callback_lock);
@@ -621,14 +622,14 @@ struct tls_context *tls_ctx_create(struct sock *sk)
 
 	mutex_init(&ctx->tx_lock);
 	rcu_assign_pointer(icsk->icsk_ulp_data, ctx);
-	ctx->sk_proto = sk->sk_prot;
+	ctx->sk_proto = READ_ONCE(sk->sk_prot);
 	return ctx;
 }
 
 static void tls_build_proto(struct sock *sk)
 {
 	int ip_ver = sk->sk_family == AF_INET6 ? TLSV6 : TLSV4;
-	const struct proto *prot = sk->sk_prot;
+	const struct proto *prot = READ_ONCE(sk->sk_prot);
 
 	/* Build IPv6 TLS whenever the address of tcpv6 _prot changes */
 	if (ip_ver == TLSV6 &&
-- 
2.24.1