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gpio: chardev: Return error for seek operations
The GPIO chardev is used for management tasks (allocating line and event handles) and does neither support read() nor write() operations. Hence it does not make much sense to allow seek operations. Currently the chardev uses noop_llseek() for its seek implementation. This function does not move the pointer and simply returns the current position (always 0 for the GPIO chardev). noop_llseek() is primarily meant for devices that can not support seek, but where there might be a user that depends on the seek() operation succeeding. For newly added devices that can not support seek operations it is recommended to use no_llseek(), which will return an error. For more information see commit6038f373a3
("llseek: automatically add .llseek fop"). Unfortunately this was overlooked when the GPIO chardev ABI was introduced. But it is highly unlikely that since then userspace applications have appeared that rely on being able to perform non-failing seek operations on a GPIO chardev file descriptor. So it should be safe to change from noop_llseel() to no_seek(). Also use nonseekable_open() in the chardev open() callback to clear the FMODE_SEEK, FMODE_PREAD and FMODE_PWRITE flags from the file. Neither of these should be set on a file that does not support seek operations. Cc: stable@vger.kernel.org Fixes:3c702e9987
("gpio: add a userspace chardev ABI for GPIOs") Signed-off-by: Lars-Peter Clausen <lars@metafoo.de> Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
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@ -913,7 +913,8 @@ static int gpio_chrdev_open(struct inode *inode, struct file *filp)
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return -ENODEV;
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get_device(&gdev->dev);
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filp->private_data = gdev;
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return 0;
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return nonseekable_open(inode, filp);
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}
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/**
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@ -938,7 +939,7 @@ static const struct file_operations gpio_fileops = {
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.release = gpio_chrdev_release,
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.open = gpio_chrdev_open,
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.owner = THIS_MODULE,
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.llseek = noop_llseek,
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.llseek = no_llseek,
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.unlocked_ioctl = gpio_ioctl,
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#ifdef CONFIG_COMPAT
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.compat_ioctl = gpio_ioctl_compat,
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