[PATCH v3] gpio: Restrict usage of GPIO chip irq members before initialization

[Shreeya Patel <shreeya.patel@xxxxxxxxxxxxx>]

GPIO chip irq members are exposed before they could be completely
initialized and this leads to race conditions.

One such issue was observed for the gc->irq.domain variable which
was accessed through the I2C interface in gpiochip_to_irq() before
it could be initialized by gpiochip_add_irqchip(). This resulted in
Kernel NULL pointer dereference.

Following are the logs for reference :-

kernel: Call Trace:
kernel:  gpiod_to_irq+0x53/0x70
kernel:  acpi_dev_gpio_irq_get_by+0x113/0x1f0
kernel:  i2c_acpi_get_irq+0xc0/0xd0
kernel:  i2c_device_probe+0x28a/0x2a0
kernel:  really_probe+0xf2/0x460
kernel: RIP: 0010:gpiochip_to_irq+0x47/0xc0

To avoid such scenarios, restrict usage of GPIO chip irq members before
they are completely initialized.

Signed-off-by: Shreeya Patel <shreeya.patel@xxxxxxxxxxxxx>
---

Changes in v3
  - Move the gc->irq.initialized check inside gpiochip_to_irq().
  - Rename gc to GPIO chip.
  - Add barrier() to avoid compiler reordering.

Changes in v2
  - Make gc_irq_initialized flag a member of gpio_irq_chip structure.
  - Make use of barrier() to avoid reordering of flag initialization
before other gc irq members are initialized.


 drivers/gpio/gpiolib.c      | 19 +++++++++++++++++++
 include/linux/gpio/driver.h |  9 +++++++++
 2 files changed, 28 insertions(+)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index defb7c464b87..4ff68f48b87f 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -1404,6 +1404,16 @@ static int gpiochip_to_irq(struct gpio_chip *gc, unsigned int offset)
 {
 	struct irq_domain *domain = gc->irq.domain;
 
+#ifdef CONFIG_GPIOLIB_IRQCHIP
+	/*
+	 * Avoid race condition with other code, which tries to lookup
+	 * an IRQ before the irqchip has been properly registered,
+	 * i.e. while gpiochip is still being brought up.
+	 */
+	if (!gc->irq.initialized)
+		return -EPROBE_DEFER;
+#endif
+
 	if (!gpiochip_irqchip_irq_valid(gc, offset))
 		return -ENXIO;
 
@@ -1593,6 +1603,15 @@ static int gpiochip_add_irqchip(struct gpio_chip *gc,
 
 	acpi_gpiochip_request_interrupts(gc);
 
+	/*
+	 * Using barrier() here to prevent compiler from reordering
+	 * gc->irq.initialized before initialization of above
+	 * GPIO chip irq members.
+	 */
+	barrier();
+
+	gc->irq.initialized = true;
+
 	return 0;
 }
 
diff --git a/include/linux/gpio/driver.h b/include/linux/gpio/driver.h
index b0728c8ad90c..f8996b46f430 100644
--- a/include/linux/gpio/driver.h
+++ b/include/linux/gpio/driver.h
@@ -218,6 +218,15 @@ struct gpio_irq_chip {
 	 */
 	bool per_parent_data;
 
+	/**
+	 * @initialized:
+	 *
+	 * Flag to track GPIO chip irq member's initialization.
+	 * This flag will make sure GPIO chip irq members are not used
+	 * before they are initialized.
+	 */
+	bool initialized;
+
 	/**
 	 * @init_hw: optional routine to initialize hardware before
 	 * an IRQ chip will be added. This is quite useful when
-- 
2.30.2