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gpiolib: cdev: fix minor race in GET_LINEINFO_WATCH

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Merge separate usage of test_bit/set_bit into test_and_set_bit to remove
the possibility of a race between the test and set.

Similarly test_bit and clear_bit.

In the existing code it is possible for two threads to race past the
test_bit and then set or clear the watch bit, and neither return EBUSY.

Signed-off-by: Kent Gibson <warthog618@gmail.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
This commit is contained in:
Kent Gibson 2020-07-08 12:15:53 +08:00 committed by Bartosz Golaszewski
parent e2b781c5f0
commit f30ef3e837
1 changed files with 5 additions and 5 deletions
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10
drivers/gpio/gpiolib-cdev.c
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@ -887,15 +887,16 @@ static long gpio_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
hwgpio = gpio_chip_hwgpio(desc);
if (test_bit(hwgpio, cdev->watched_lines))
if (test_and_set_bit(hwgpio, cdev->watched_lines))
return -EBUSY;
gpio_desc_to_lineinfo(desc, &lineinfo);
if (copy_to_user(ip, &lineinfo, sizeof(lineinfo)))
if (copy_to_user(ip, &lineinfo, sizeof(lineinfo))) {
clear_bit(hwgpio, cdev->watched_lines);
return -EFAULT;
}
set_bit(hwgpio, cdev->watched_lines);
return 0;
} else if (cmd == GPIO_GET_LINEINFO_UNWATCH_IOCTL) {
if (copy_from_user(&offset, ip, sizeof(offset)))
@ -907,10 +908,9 @@ static long gpio_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
hwgpio = gpio_chip_hwgpio(desc);
if (!test_bit(hwgpio, cdev->watched_lines))
if (!test_and_clear_bit(hwgpio, cdev->watched_lines))
return -EBUSY;
clear_bit(hwgpio, cdev->watched_lines);
return 0;
}
return -EINVAL;