[rft, PATCH v5 1/1] gpiolib: fix memory leak in gpiochip_setup_dev()

[Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>]

From: Zeng Heng <zengheng4@xxxxxxxxxx>

Here is a backtrace report about memory leak detected in
gpiochip_setup_dev():

unreferenced object 0xffff88810b406400 (size 512):
  comm "python3", pid 1682, jiffies 4295346908 (age 24.090s)
  backtrace:
    kmalloc_trace
    device_add		device_private_init at drivers/base/core.c:3361
			(inlined by) device_add at drivers/base/core.c:3411
    cdev_device_add
    gpiolib_cdev_register
    gpiochip_setup_dev
    gpiochip_add_data_with_key

gcdev_register() & gcdev_unregister() would call device_add() &
device_del() (no matter CONFIG_GPIO_CDEV is enabled or not) to
register/unregister device.

However, if device_add() succeeds, some resource (like
struct device_private allocated by device_private_init())
is not released by device_del().

Therefore, after device_add() succeeds by gcdev_register(), it
needs to call put_device() to release resource in the error handle
path.

Here we move forward the register of release function, and let it
release every piece of resource by put_device() instead of kfree().

While at it, fix another subtle issue, i.e. when gc->ngpio is equal
to 0, we still call kcalloc() and, in case of further error, kfree()
on the ZERO_PTR pointer, which is not NULL. It's not a bug per se,
but rather waste of the resources and potentially wrong expectation
about contents of the gdev->descs variable.

Fixes: 159f3cd92f17 ("gpiolib: Defer gpio device setup until after gpiolib initialization")
Signed-off-by: Zeng Heng <zengheng4@xxxxxxxxxx>
Co-developed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
---
changes in v5 (done by Andy):
  - refactored to avoid double checks on the same conditionals
  - moved kcalloc() after validating its parameter
  - compiled tested only by me (Andy)
changes in v4:
  - add gpiochip_print_register_fail()
changes in v3:
  - use put_device() instead of kfree() explicitly
changes in v2:
  - correct fixes tag

 drivers/gpio/gpiolib.c | 42 ++++++++++++++++++++++++++----------------
 1 file changed, 26 insertions(+), 16 deletions(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index caa747fdcb72..119c9c3a2a50 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -580,12 +580,13 @@ static int gpiochip_setup_dev(struct gpio_device *gdev)
 	if (ret)
 		return ret;
 
+	/* From this point, the .release() function cleans up gpio_device */
+	gdev->dev.release = gpiodevice_release;
+
 	ret = gpiochip_sysfs_register(gdev);
 	if (ret)
 		goto err_remove_device;
 
-	/* From this point, the .release() function cleans up gpio_device */
-	gdev->dev.release = gpiodevice_release;
 	dev_dbg(&gdev->dev, "registered GPIOs %d to %d on %s\n", gdev->base,
 		gdev->base + gdev->ngpio - 1, gdev->chip->label ? : "generic");
 
@@ -651,10 +652,10 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 	struct fwnode_handle *fwnode = NULL;
 	struct gpio_device *gdev;
 	unsigned long flags;
-	int base = gc->base;
 	unsigned int i;
+	u32 ngpios = 0;
+	int base = 0;
 	int ret = 0;
-	u32 ngpios;
 
 	/* If the calling driver did not initialize firmware node, do it here */
 	if (gc->fwnode)
@@ -696,17 +697,12 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 	else
 		gdev->owner = THIS_MODULE;
 
-	gdev->descs = kcalloc(gc->ngpio, sizeof(gdev->descs[0]), GFP_KERNEL);
-	if (!gdev->descs) {
-		ret = -ENOMEM;
-		goto err_free_dev_name;
-	}
-
 	/*
 	 * Try the device properties if the driver didn't supply the number
 	 * of GPIO lines.
 	 */
-	if (gc->ngpio == 0) {
+	ngpios = gc->ngpio;
+	if (ngpios == 0) {
 		ret = device_property_read_u32(&gdev->dev, "ngpios", &ngpios);
 		if (ret == -ENODATA)
 			/*
@@ -717,7 +713,7 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 			 */
 			ngpios = 0;
 		else if (ret)
-			goto err_free_descs;
+			goto err_free_dev_name;
 
 		gc->ngpio = ngpios;
 	}
@@ -725,13 +721,19 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 	if (gc->ngpio == 0) {
 		chip_err(gc, "tried to insert a GPIO chip with zero lines\n");
 		ret = -EINVAL;
-		goto err_free_descs;
+		goto err_free_dev_name;
 	}
 
 	if (gc->ngpio > FASTPATH_NGPIO)
 		chip_warn(gc, "line cnt %u is greater than fast path cnt %u\n",
 			  gc->ngpio, FASTPATH_NGPIO);
 
+	gdev->descs = kcalloc(gc->ngpio, sizeof(*gdev->descs), GFP_KERNEL);
+	if (!gdev->descs) {
+		ret = -ENOMEM;
+		goto err_free_dev_name;
+	}
+
 	gdev->label = kstrdup_const(gc->label ?: "unknown", GFP_KERNEL);
 	if (!gdev->label) {
 		ret = -ENOMEM;
@@ -750,11 +752,13 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 	 * it may be a pipe dream. It will not happen before we get rid
 	 * of the sysfs interface anyways.
 	 */
+	base = gc->base;
 	if (base < 0) {
 		base = gpiochip_find_base(gc->ngpio);
 		if (base < 0) {
-			ret = base;
 			spin_unlock_irqrestore(&gpio_lock, flags);
+			ret = base;
+			base = 0;
 			goto err_free_label;
 		}
 		/*
@@ -868,6 +872,11 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 err_free_gpiochip_mask:
 	gpiochip_remove_pin_ranges(gc);
 	gpiochip_free_valid_mask(gc);
+	if (gdev->dev.release) {
+		/* release() has been registered by gpiochip_setup_dev() */
+		put_device(&gdev->dev);
+		goto err_print_message;
+	}
 err_remove_from_list:
 	spin_lock_irqsave(&gpio_lock, flags);
 	list_del(&gdev->list);
@@ -881,13 +890,14 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
 err_free_ida:
 	ida_free(&gpio_ida, gdev->id);
 err_free_gdev:
+	kfree(gdev);
+err_print_message:
 	/* failures here can mean systems won't boot... */
 	if (ret != -EPROBE_DEFER) {
 		pr_err("%s: GPIOs %d..%d (%s) failed to register, %d\n", __func__,
-		       gdev->base, gdev->base + gdev->ngpio - 1,
+		       base, base + (int)ngpios - 1,
 		       gc->label ? : "generic", ret);
 	}
-	kfree(gdev);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(gpiochip_add_data_with_key);
-- 
2.35.1