thunderbolt: Fix NULL dereference in tb_remove_work()grafted

There is a slight race between tb_remove_work() and tb_domain_remove()
which leads to dereferencing a NULL tb->root_switch pointer inside
tb_free_unplugged_xdomains():

        Thread A                            Thread B

  tb_remove_work()
                                    tb_domain_remove()
                                      mutex_lock(&tb->lock)
                                      tb_stop()
                                        /* doesn't cancel a running callback */
                                        cancel_delayed_work(&tcm->remove_work)
                                        ...
                                        tb_switch_remove(tb->root_switch)
                                        tb->root_switch = NULL
                                      mutex_unlock(&tb->lock)
    mutex_lock(&tb->lock)
    ...
    /* without checking ->root_switch */
    tb_free_unplugged_xdomains(tb->root_switch)
    mutex_unlock(&tb->lock)

Commit a8937f35cf39 ("thunderbolt: Remove XDomain from the bus without
holding tb->lock") doesn't seem right to move tb_free_unplugged_xdomains()
out of the &tb->lock section and the check for tb->root_switch, in
particular.  It states:

  For this reason separate removing the XDomain from the topology data
  structures (where we need the lock) from unregistering the device from
  the bus (where remove callbacks of the drivers are being called).

tb_free_unplugged_xdomains() belongs to the former group of functions
requiring the lock.  And it also calls tb_xdomain_remove() which should
only be called with &tb->lock held.

Found by Linux Verification Center (linuxtesting.org) with Svace static
analysis tool.

Fixes: a8937f35cf39 ("thunderbolt: Remove XDomain from the bus without holding tb->lock")
Cc: stable@vger.kernel.org
Signed-off-by: Fedor Pchelkin <pchelkin@ispras.ru>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>

3 files changed, 219 insertions, 0 deletions

diff --git a/virt/lib/Kconfig b/virt/lib/Kconfig
new file mode 100644
index 000000000..2d9523b71
--- /dev/null
+++ b/virt/lib/Kconfig
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0-only
+config IRQ_BYPASS_MANAGER
+	tristate
diff --git a/virt/lib/Makefile b/virt/lib/Makefile
new file mode 100644
index 000000000..bd7f9a78b
--- /dev/null
+++ b/virt/lib/Makefile
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+obj-$(CONFIG_IRQ_BYPASS_MANAGER) += irqbypass.o
diff --git a/virt/lib/irqbypass.c b/virt/lib/irqbypass.c
new file mode 100644
index 000000000..62c160200
--- /dev/null
+++ b/virt/lib/irqbypass.c
@@ -0,0 +1,214 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * IRQ offload/bypass manager
+ *
+ * Copyright (C) 2015 Red Hat, Inc.
+ * Copyright (c) 2015 Linaro Ltd.
+ *
+ * Various virtualization hardware acceleration techniques allow bypassing or
+ * offloading interrupts received from devices around the host kernel.  Posted
+ * Interrupts on Intel VT-d systems can allow interrupts to be received
+ * directly by a virtual machine.  ARM IRQ Forwarding allows forwarded physical
+ * interrupts to be directly deactivated by the guest.  This manager allows
+ * interrupt producers and consumers to find each other to enable this sort of
+ * bypass.
+ */
+
+#include <linux/irqbypass.h>
+#include <linux/list.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+
+MODULE_LICENSE("GPL v2");
+MODULE_DESCRIPTION("IRQ bypass manager utility module");
+
+static DEFINE_XARRAY(producers);
+static DEFINE_XARRAY(consumers);
+static DEFINE_MUTEX(lock);
+
+/* @lock must be held when calling connect */
+static int __connect(struct irq_bypass_producer *prod,
+		     struct irq_bypass_consumer *cons)
+{
+	int ret = 0;
+
+	if (prod->stop)
+		prod->stop(prod);
+	if (cons->stop)
+		cons->stop(cons);
+
+	if (prod->add_consumer)
+		ret = prod->add_consumer(prod, cons);
+
+	if (!ret) {
+		ret = cons->add_producer(cons, prod);
+		if (ret && prod->del_consumer)
+			prod->del_consumer(prod, cons);
+	}
+
+	if (cons->start)
+		cons->start(cons);
+	if (prod->start)
+		prod->start(prod);
+
+	if (!ret) {
+		prod->consumer = cons;
+		cons->producer = prod;
+	}
+	return ret;
+}
+
+/* @lock must be held when calling disconnect */
+static void __disconnect(struct irq_bypass_producer *prod,
+			 struct irq_bypass_consumer *cons)
+{
+	if (prod->stop)
+		prod->stop(prod);
+	if (cons->stop)
+		cons->stop(cons);
+
+	cons->del_producer(cons, prod);
+
+	if (prod->del_consumer)
+		prod->del_consumer(prod, cons);
+
+	if (cons->start)
+		cons->start(cons);
+	if (prod->start)
+		prod->start(prod);
+
+	prod->consumer = NULL;
+	cons->producer = NULL;
+}
+
+/**
+ * irq_bypass_register_producer - register IRQ bypass producer
+ * @producer: pointer to producer structure
+ * @eventfd: pointer to the eventfd context associated with the producer
+ * @irq: Linux IRQ number of the underlying producer device
+ *
+ * Add the provided IRQ producer to the set of producers and connect with the
+ * consumer with a matching eventfd, if one exists.
+ */
+int irq_bypass_register_producer(struct irq_bypass_producer *producer,
+				 struct eventfd_ctx *eventfd, int irq)
+{
+	unsigned long index = (unsigned long)eventfd;
+	struct irq_bypass_consumer *consumer;
+	int ret;
+
+	if (WARN_ON_ONCE(producer->eventfd))
+		return -EINVAL;
+
+	producer->irq = irq;
+
+	guard(mutex)(&lock);
+
+	ret = xa_insert(&producers, index, producer, GFP_KERNEL);
+	if (ret)
+		return ret;
+
+	consumer = xa_load(&consumers, index);
+	if (consumer) {
+		ret = __connect(producer, consumer);
+		if (ret) {
+			WARN_ON_ONCE(xa_erase(&producers, index) != producer);
+			return ret;
+		}
+	}
+
+	producer->eventfd = eventfd;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(irq_bypass_register_producer);
+
+/**
+ * irq_bypass_unregister_producer - unregister IRQ bypass producer
+ * @producer: pointer to producer structure
+ *
+ * Remove a previously registered IRQ producer (note, it's safe to call this
+ * even if registration was unsuccessful).  Disconnect from the associated
+ * consumer, if one exists.
+ */
+void irq_bypass_unregister_producer(struct irq_bypass_producer *producer)
+{
+	unsigned long index = (unsigned long)producer->eventfd;
+
+	if (!producer->eventfd)
+		return;
+
+	guard(mutex)(&lock);
+
+	if (producer->consumer)
+		__disconnect(producer, producer->consumer);
+
+	WARN_ON_ONCE(xa_erase(&producers, index) != producer);
+	producer->eventfd = NULL;
+}
+EXPORT_SYMBOL_GPL(irq_bypass_unregister_producer);
+
+/**
+ * irq_bypass_register_consumer - register IRQ bypass consumer
+ * @consumer: pointer to consumer structure
+ * @eventfd: pointer to the eventfd context associated with the consumer
+ *
+ * Add the provided IRQ consumer to the set of consumers and connect with the
+ * producer with a matching eventfd, if one exists.
+ */
+int irq_bypass_register_consumer(struct irq_bypass_consumer *consumer,
+				 struct eventfd_ctx *eventfd)
+{
+	unsigned long index = (unsigned long)eventfd;
+	struct irq_bypass_producer *producer;
+	int ret;
+
+	if (WARN_ON_ONCE(consumer->eventfd))
+		return -EINVAL;
+
+	if (!consumer->add_producer || !consumer->del_producer)
+		return -EINVAL;
+
+	guard(mutex)(&lock);
+
+	ret = xa_insert(&consumers, index, consumer, GFP_KERNEL);
+	if (ret)
+		return ret;
+
+	producer = xa_load(&producers, index);
+	if (producer) {
+		ret = __connect(producer, consumer);
+		if (ret) {
+			WARN_ON_ONCE(xa_erase(&consumers, index) != consumer);
+			return ret;
+		}
+	}
+
+	consumer->eventfd = eventfd;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(irq_bypass_register_consumer);
+
+/**
+ * irq_bypass_unregister_consumer - unregister IRQ bypass consumer
+ * @consumer: pointer to consumer structure
+ *
+ * Remove a previously registered IRQ consumer (note, it's safe to call this
+ * even if registration was unsuccessful).  Disconnect from the associated
+ * producer, if one exists.
+ */
+void irq_bypass_unregister_consumer(struct irq_bypass_consumer *consumer)
+{
+	unsigned long index = (unsigned long)consumer->eventfd;
+
+	if (!consumer->eventfd)
+		return;
+
+	guard(mutex)(&lock);
+
+	if (consumer->producer)
+		__disconnect(consumer->producer, consumer);
+
+	WARN_ON_ONCE(xa_erase(&consumers, index) != consumer);
+	consumer->eventfd = NULL;
+}
+EXPORT_SYMBOL_GPL(irq_bypass_unregister_consumer);