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>

1 files changed, 153 insertions, 0 deletions

diff --git a/drivers/clocksource/timer-goldfish.c b/drivers/clocksource/timer-goldfish.c
new file mode 100644
index 000000000..3fe12c7ee
--- /dev/null
+++ b/drivers/clocksource/timer-goldfish.c
@@ -0,0 +1,153 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/interrupt.h>
+#include <linux/ioport.h>
+#include <linux/clocksource.h>
+#include <linux/clockchips.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/goldfish.h>
+#include <clocksource/timer-goldfish.h>
+
+struct goldfish_timer {
+	struct clocksource cs;
+	struct clock_event_device ced;
+	struct resource res;
+	void __iomem *base;
+};
+
+static struct goldfish_timer *ced_to_gf(struct clock_event_device *ced)
+{
+	return container_of(ced, struct goldfish_timer, ced);
+}
+
+static struct goldfish_timer *cs_to_gf(struct clocksource *cs)
+{
+	return container_of(cs, struct goldfish_timer, cs);
+}
+
+static u64 goldfish_timer_read(struct clocksource *cs)
+{
+	struct goldfish_timer *timerdrv = cs_to_gf(cs);
+	void __iomem *base = timerdrv->base;
+	u32 time_low, time_high;
+	u64 ticks;
+
+	/*
+	 * time_low: get low bits of current time and update time_high
+	 * time_high: get high bits of time at last time_low read
+	 */
+	time_low = gf_ioread32(base + TIMER_TIME_LOW);
+	time_high = gf_ioread32(base + TIMER_TIME_HIGH);
+
+	ticks = ((u64)time_high << 32) | time_low;
+
+	return ticks;
+}
+
+static int goldfish_timer_set_oneshot(struct clock_event_device *evt)
+{
+	struct goldfish_timer *timerdrv = ced_to_gf(evt);
+	void __iomem *base = timerdrv->base;
+
+	gf_iowrite32(0, base + TIMER_ALARM_HIGH);
+	gf_iowrite32(0, base + TIMER_ALARM_LOW);
+	gf_iowrite32(1, base + TIMER_IRQ_ENABLED);
+
+	return 0;
+}
+
+static int goldfish_timer_shutdown(struct clock_event_device *evt)
+{
+	struct goldfish_timer *timerdrv = ced_to_gf(evt);
+	void __iomem *base = timerdrv->base;
+
+	gf_iowrite32(0, base + TIMER_IRQ_ENABLED);
+
+	return 0;
+}
+
+static int goldfish_timer_next_event(unsigned long delta,
+				     struct clock_event_device *evt)
+{
+	struct goldfish_timer *timerdrv = ced_to_gf(evt);
+	void __iomem *base = timerdrv->base;
+	u64 now;
+
+	now = goldfish_timer_read(&timerdrv->cs);
+
+	now += delta;
+
+	gf_iowrite32(upper_32_bits(now), base + TIMER_ALARM_HIGH);
+	gf_iowrite32(lower_32_bits(now), base + TIMER_ALARM_LOW);
+
+	return 0;
+}
+
+static irqreturn_t goldfish_timer_irq(int irq, void *dev_id)
+{
+	struct goldfish_timer *timerdrv = dev_id;
+	struct clock_event_device *evt = &timerdrv->ced;
+	void __iomem *base = timerdrv->base;
+
+	gf_iowrite32(1, base + TIMER_CLEAR_INTERRUPT);
+
+	evt->event_handler(evt);
+
+	return IRQ_HANDLED;
+}
+
+int __init goldfish_timer_init(int irq, void __iomem *base)
+{
+	struct goldfish_timer *timerdrv;
+	int ret;
+
+	timerdrv = kzalloc_obj(*timerdrv);
+	if (!timerdrv)
+		return -ENOMEM;
+
+	timerdrv->base = base;
+
+	timerdrv->ced = (struct clock_event_device){
+		.name			= "goldfish_timer",
+		.features		= CLOCK_EVT_FEAT_ONESHOT,
+		.set_state_shutdown	= goldfish_timer_shutdown,
+		.set_state_oneshot      = goldfish_timer_set_oneshot,
+		.set_next_event		= goldfish_timer_next_event,
+	};
+
+	timerdrv->res = (struct resource){
+		.name  = "goldfish_timer",
+		.start = (unsigned long)base,
+		.end   = (unsigned long)base + 0xfff,
+	};
+
+	ret = request_resource(&iomem_resource, &timerdrv->res);
+	if (ret) {
+		pr_err("Cannot allocate '%s' resource\n", timerdrv->res.name);
+		return ret;
+	}
+
+	timerdrv->cs = (struct clocksource){
+		.name		= "goldfish_timer",
+		.rating		= 400,
+		.read		= goldfish_timer_read,
+		.mask		= CLOCKSOURCE_MASK(64),
+		.flags		= 0,
+		.max_idle_ns	= LONG_MAX,
+	};
+
+	clocksource_register_hz(&timerdrv->cs, NSEC_PER_SEC);
+
+	ret = request_irq(irq, goldfish_timer_irq, IRQF_TIMER,
+			  "goldfish_timer", timerdrv);
+	if (ret) {
+		pr_err("Couldn't register goldfish-timer interrupt\n");
+		return ret;
+	}
+
+	clockevents_config_and_register(&timerdrv->ced, NSEC_PER_SEC,
+					1, 0xffffffff);
+
+	return 0;
+}