[PATCH v2] phy: phy-bcm-ns2-usbdrd: cancel extcon work on unbind to avoid use-after-free

[hyunjungg <hj351016@gmail.com>]

From: Hyunjung Ko <hj351016@gmail.com>

ns2_drd_phy_probe() schedules driver->wq_extcon (extcon_work), which is
also queued from the ID/VBUS GPIO interrupt handler gpio_irq_handler().
The work handler dereferences the driver data via container_of().

struct ns2_phy_driver is allocated with devm_kzalloc() and the driver has
no remove callback, so on unbind devres frees it after probe's resources
are released. The GPIO interrupts are requested with devm_request_irq(),
and so released by devres; free_irq() only stops further interrupts, it
does not cancel a delayed work that is already queued. probe() queues
wq_extcon with a debounce delay before returning, and the GPIO interrupt
can queue it too, so on unbind the pending work can run after
ns2_phy_driver has been freed, dereferencing freed memory (use-after-free).

Register the work with devm_delayed_work_autocancel() instead of
INIT_DELAYED_WORK(). It is set up before the GPIO interrupts are
requested, so on unwind devres frees the interrupts first - after which
the work can no longer be queued - and then cancels the work while the
driver data is still valid. extcon_work() does not re-queue itself, so a
single cancel drains it.

Found by static analysis and code review; not runtime-reproduced (needs
Broadcom Northstar2 USB DRD PHY hardware).

Fixes: 787f24543c4a ("phy: phy-bcm-ns2-usbdrd: Broadcom USB DRD PHY driver for Northstar2")
Cc: stable@vger.kernel.org
Signed-off-by: Hyunjung Ko <hj351016@gmail.com>
---
Changes in v2:
- Reword the commit message: the GPIO interrupts are requested with
  devm_request_irq() and released by devres (not "released with
  devm_request_irq()") (Ray Jui).
- Place the new #include <linux/devm-helpers.h> in alphabetical order,
  after <linux/delay.h> (Ray Jui).

 drivers/phy/broadcom/phy-bcm-ns2-usbdrd.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/phy/broadcom/phy-bcm-ns2-usbdrd.c b/drivers/phy/broadcom/phy-bcm-ns2-usbdrd.c
index 171bf09..4b8930b 100644
--- a/drivers/phy/broadcom/phy-bcm-ns2-usbdrd.c
+++ b/drivers/phy/broadcom/phy-bcm-ns2-usbdrd.c
@@ -2,6 +2,7 @@
 // Copyright (C) 2017 Broadcom

 #include <linux/delay.h>
+#include <linux/devm-helpers.h>
 #include <linux/extcon-provider.h>
 #include <linux/gpio/consumer.h>
 #include <linux/init.h>
@@ -339,7 +340,9 @@ static int ns2_drd_phy_probe(struct platform_device *pdev)
 	if (ret < 0)
 		driver->debounce_jiffies = msecs_to_jiffies(GPIO_DELAY);

-	INIT_DELAYED_WORK(&driver->wq_extcon, extcon_work);
+	ret = devm_delayed_work_autocancel(dev, &driver->wq_extcon, extcon_work);
+	if (ret)
+		return ret;

 	driver->id_irq = gpiod_to_irq(driver->id_gpiod);
 	if (driver->id_irq < 0) {
--
2.43.0