ftrace: Synchronize the initialization of ftrace_opsgrafted

There's some internal state that ftrace_ops needs to have set, but since
it can be declared outside of the ftrace.c code, it calls
ftrace_ops_init() on the ops in every global function. The issue is that
if two tasks call it on the same ops at the same time it is possible to
have the initialization of one corrupt the initialization of the other
call.

Create a ops_mutex to use to synchronize every initialization of the
ftrace_ops. The mutex is taken within checking the ftrace_ops flag that
states it was initializied but the flag is checked again after the mutex
has been taken. Checking first outside the mutex allows it to shortcut
having to take the mutex. But then the check needs to be done again after
the mute is taken in case of races.

Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260902095501.6b59af20@gandalf.local.home
Fixes: f04f24fb7e48d ("ftrace, kprobes: Fix a deadlock on ftrace_regex_lock")
Reported-by: sashiko-bot@kernel.org
Close: https://lore.kernel.org/all/20260829025528.49A831F000E9@smtp.kernel.org/
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 102 insertions, 0 deletions

diff --git a/net/802/stp.c b/net/802/stp.c
new file mode 100644
index 000000000..03c9f75e9
--- /dev/null
+++ b/net/802/stp.c
@@ -0,0 +1,102 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *	STP SAP demux
+ *
+ *	Copyright (c) 2008 Patrick McHardy <kaber@trash.net>
+ */
+#include <linux/mutex.h>
+#include <linux/skbuff.h>
+#include <linux/etherdevice.h>
+#include <linux/llc.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+#include <net/llc.h>
+#include <net/llc_pdu.h>
+#include <net/stp.h>
+
+/* 01:80:c2:00:00:20 - 01:80:c2:00:00:2F */
+#define GARP_ADDR_MIN	0x20
+#define GARP_ADDR_MAX	0x2F
+#define GARP_ADDR_RANGE	(GARP_ADDR_MAX - GARP_ADDR_MIN)
+
+static const struct stp_proto __rcu *garp_protos[GARP_ADDR_RANGE + 1] __read_mostly;
+static const struct stp_proto __rcu *stp_proto __read_mostly;
+
+static struct llc_sap *sap __read_mostly;
+static unsigned int sap_registered;
+static DEFINE_MUTEX(stp_proto_mutex);
+
+/* Called under rcu_read_lock from LLC */
+static int stp_pdu_rcv(struct sk_buff *skb, struct net_device *dev,
+		       struct packet_type *pt, struct net_device *orig_dev)
+{
+	const struct ethhdr *eh = eth_hdr(skb);
+	const struct llc_pdu_un *pdu = llc_pdu_un_hdr(skb);
+	const struct stp_proto *proto;
+
+	if (pdu->ssap != LLC_SAP_BSPAN ||
+	    pdu->dsap != LLC_SAP_BSPAN ||
+	    pdu->ctrl_1 != LLC_PDU_TYPE_U)
+		goto err;
+
+	if (eh->h_dest[5] >= GARP_ADDR_MIN && eh->h_dest[5] <= GARP_ADDR_MAX) {
+		proto = rcu_dereference(garp_protos[eh->h_dest[5] -
+						    GARP_ADDR_MIN]);
+		if (proto &&
+		    !ether_addr_equal(eh->h_dest, proto->group_address))
+			goto err;
+	} else
+		proto = rcu_dereference(stp_proto);
+
+	if (!proto)
+		goto err;
+
+	proto->rcv(proto, skb, dev);
+	return 0;
+
+err:
+	kfree_skb(skb);
+	return 0;
+}
+
+int stp_proto_register(const struct stp_proto *proto)
+{
+	int err = 0;
+
+	mutex_lock(&stp_proto_mutex);
+	if (sap_registered++ == 0) {
+		sap = llc_sap_open(LLC_SAP_BSPAN, stp_pdu_rcv);
+		if (!sap) {
+			err = -ENOMEM;
+			goto out;
+		}
+	}
+	if (is_zero_ether_addr(proto->group_address))
+		rcu_assign_pointer(stp_proto, proto);
+	else
+		rcu_assign_pointer(garp_protos[proto->group_address[5] -
+					       GARP_ADDR_MIN], proto);
+out:
+	mutex_unlock(&stp_proto_mutex);
+	return err;
+}
+EXPORT_SYMBOL_GPL(stp_proto_register);
+
+void stp_proto_unregister(const struct stp_proto *proto)
+{
+	mutex_lock(&stp_proto_mutex);
+	if (is_zero_ether_addr(proto->group_address))
+		RCU_INIT_POINTER(stp_proto, NULL);
+	else
+		RCU_INIT_POINTER(garp_protos[proto->group_address[5] -
+					       GARP_ADDR_MIN], NULL);
+	synchronize_rcu();
+
+	if (--sap_registered == 0)
+		llc_sap_put(sap);
+	mutex_unlock(&stp_proto_mutex);
+}
+EXPORT_SYMBOL_GPL(stp_proto_unregister);
+
+MODULE_DESCRIPTION("SAP demux for IEEE 802.1D Spanning Tree Protocol (STP)");
+MODULE_LICENSE("GPL");