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

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Date:   Thu, 10 Mar 2022 18:51:07 +0530
From:   Shreeya Patel <shreeya.patel@...labora.com>
To:     linus.walleij@...aro.org, brgl@...ev.pl, krisman@...labora.com
Cc:     linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel@...labora.com, andy.shevchenko@...il.com,
        Shreeya Patel <shreeya.patel@...labora.com>
Subject: [PATCH] gpio: Restrict usage of gc irq members before initialization

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@...labora.com>
---

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