Merge branch 'net-tls-Annotate-lockless-access-to-sk_prot'

Jakub Sitnicki says:

====================
net/tls: Annotate lockless access to sk_prot

We have recently noticed that there is a case of lockless read/write to
sk->sk_prot [0]. sockmap code on psock tear-down writes to sk->sk_prot,
while holding sk_callback_lock. Concurrently, tcp can access it. Usually to
read out the sk_prot pointer and invoke one of the ops,
sk->sk_prot->handler().

The lockless write (lockless in regard to concurrent reads) happens 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 sites that access sk_prot with
READ_ONCE/WRITE_ONCE.

This series kicks off the effort to do it. Starting with net/tls.

[0] https://lore.kernel.org/bpf/a6bf279e-a998-84ab-4371-cd6c1ccbca5d@gmail.com/
[1] https://lwn.net/Articles/793253/
[2] https://github.com/google/ktsan/wiki/READ_ONCE-and-WRITE_ONCE
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 16 insertions, 14 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 82225bcc1117..156efce50dbd 100644
--- a/net/tls/tls_main.c
+++ b/net/tls/tls_main.c
@@ -63,13 +63,14 @@ static DEFINE_MUTEX(tcpv4_prot_mutex);
 static struct proto tls_prots[TLS_NUM_PROTS][TLS_NUM_CONFIG][TLS_NUM_CONFIG];
 static struct proto_ops tls_sw_proto_ops;
 static void build_protos(struct proto prot[TLS_NUM_CONFIG][TLS_NUM_CONFIG],
-			 struct proto *base);
+			 const struct proto *base);
 
 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);
@@ -621,38 +622,39 @@ 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 = READ_ONCE(sk->sk_prot);
 
 	/* Build IPv6 TLS whenever the address of tcpv6 _prot changes */
 	if (ip_ver == TLSV6 &&
-	    unlikely(sk->sk_prot != smp_load_acquire(&saved_tcpv6_prot))) {
+	    unlikely(prot != smp_load_acquire(&saved_tcpv6_prot))) {
 		mutex_lock(&tcpv6_prot_mutex);
-		if (likely(sk->sk_prot != saved_tcpv6_prot)) {
-			build_protos(tls_prots[TLSV6], sk->sk_prot);
-			smp_store_release(&saved_tcpv6_prot, sk->sk_prot);
+		if (likely(prot != saved_tcpv6_prot)) {
+			build_protos(tls_prots[TLSV6], prot);
+			smp_store_release(&saved_tcpv6_prot, prot);
 		}
 		mutex_unlock(&tcpv6_prot_mutex);
 	}
 
 	if (ip_ver == TLSV4 &&
-	    unlikely(sk->sk_prot != smp_load_acquire(&saved_tcpv4_prot))) {
+	    unlikely(prot != smp_load_acquire(&saved_tcpv4_prot))) {
 		mutex_lock(&tcpv4_prot_mutex);
-		if (likely(sk->sk_prot != saved_tcpv4_prot)) {
-			build_protos(tls_prots[TLSV4], sk->sk_prot);
-			smp_store_release(&saved_tcpv4_prot, sk->sk_prot);
+		if (likely(prot != saved_tcpv4_prot)) {
+			build_protos(tls_prots[TLSV4], prot);
+			smp_store_release(&saved_tcpv4_prot, prot);
 		}
 		mutex_unlock(&tcpv4_prot_mutex);
 	}
 }
 
 static void build_protos(struct proto prot[TLS_NUM_CONFIG][TLS_NUM_CONFIG],
-			 struct proto *base)
+			 const struct proto *base)
 {
 	prot[TLS_BASE][TLS_BASE] = *base;
 	prot[TLS_BASE][TLS_BASE].setsockopt	= tls_setsockopt;