[PATCH] gpio: Restrict usage of gc irq members before initialization

[Shreeya Patel]

gc 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.

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

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

Following is the NULL pointer dereference Oops 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:  driver_probe_device+0xe8/0x160
kernel:  ? driver_allows_async_probing+0x50/0x50
kernel:  bus_for_each_drv+0x8f/0xd0
kernel:  __device_attach_async_helper+0x9f/0xf0
kernel:  async_run_entry_fn+0x2e/0x110
kernel:  process_one_work+0x214/0x3e0
kernel:  worker_thread+0x4d/0x3d0
kernel:  ? process_one_work+0x3e0/0x3e0
kernel:  kthread+0x133/0x150
kernel:  ? kthread_associate_blkcg+0xc0/0xc0
kernel:  ret_from_fork+0x22/0x30
kernel: CR2: 0000000000000028
kernel: ---[ end trace d0f5a7a0e0eb268f ]---
kernel: RIP: 0010:gpiochip_to_irq+0x47/0xc0

 drivers/gpio/gpiolib.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index defb7c464b87..2c6f382ff159 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -90,6 +90,7 @@ static int gpiochip_irqchip_init_valid_mask(struct gpio_chip *gc);
 static void gpiochip_irqchip_free_valid_mask(struct gpio_chip *gc);
 
 static bool gpiolib_initialized;
+bool gc_irq_initialized;
 
 static inline void desc_set_label(struct gpio_desc *d, const char *label)
 {
@@ -1593,6 +1594,8 @@ static int gpiochip_add_irqchip(struct gpio_chip *gc,
 
 	acpi_gpiochip_request_interrupts(gc);
 
+	gc_irq_initialized = true;
+
 	return 0;
 }
 
@@ -3138,7 +3141,7 @@ int gpiod_to_irq(const struct gpio_desc *desc)
 
 	gc = desc->gdev->chip;
 	offset = gpio_chip_hwgpio(desc);
-	if (gc->to_irq) {
+	if (gc->to_irq && gc_irq_initialized) {
 		int retirq = gc->to_irq(gc, offset);
 
 		/* Zero means NO_IRQ */
-- 
2.30.2