On Thu, Jun 6, 2024, at 08:13, He Zhe wrote:
> diff --git a/drivers/char/hpet.c b/drivers/char/hpet.c
> index d51fc8321d41..025a5905a370 100644
> --- a/drivers/char/hpet.c
> +++ b/drivers/char/hpet.c
> @@ -269,7 +269,8 @@ hpet_read(struct file *file, char __user *buf,
> size_t count, loff_t * ppos)
> if (!devp->hd_ireqfreq)
> return -EIO;
>
> - if (count < sizeof(unsigned long))
> + if ((sizeof(int) != sizeof(long) && count < sizeof(compat_ulong_t)) ||
> + (sizeof(int) == sizeof(long) && count < sizeof(unsigned long)))
> return -EINVAL;
>
> add_wait_queue(&devp->hd_waitqueue, &wait);
> @@ -294,9 +295,15 @@ hpet_read(struct file *file, char __user *buf,
> size_t count, loff_t * ppos)
> schedule();
> }
>
> - retval = put_user(data, (unsigned long __user *)buf);
> - if (!retval)
> - retval = sizeof(unsigned long);
> + if (sizeof(int) != sizeof(long) && count == sizeof(compat_ulong_t)) {
> + retval = put_user(data, (compat_ulong_t __user *)buf);
> + if (!retval)
> + retval = sizeof(compat_ulong_t);
> + } else {
> + retval = put_user(data, (unsigned long __user *)buf);
> + if (!retval)
> + retval = sizeof(unsigned long);
> + }
This does not look right: you are changing the behavior for
both 32-bit and 64-bit mode, and now choose the output based
on how many bytes userspace asked for. This has at least two
problems:
- if userspace asks for 5 to 7 bytes on a 64-bit kernel,
it returns 8 bytes, overflowing the provided buffer.
- when 32-bit userspace asks for 8 or more bytes, it
gets 8 bytes instead of 4.
Instead, you should check in_compat_syscall() to see
which output matches the running task.
> @@ -651,14 +658,23 @@ struct compat_hpet_info {
> unsigned short hi_timer;
> };
>
> +#define COMPAT_HPET_INFO _IOR('h', 0x03, struct compat_hpet_info)
> +#define COMPAT_HPET_IRQFREQ _IOW('h', 0x6, compat_ulong_t)
Right, it looks this was missing from my original change 54066a57c584
("hpet: kill BKL, add compat_ioctl").
COMPAT_HPET_IRQFREQ should probably have a comment about the
command code being wrong.
> mutex_lock(&hpet_mutex);
> - err = hpet_ioctl_common(file->private_data, cmd, arg, &info);
> + err = hpet_ioctl_common(file->private_data, cmd, (unsigned
> long)compat_ptr(arg), &info);
> mutex_unlock(&hpet_mutex);
While this works on x86, this is not a correct use of
compat_ptr() on architectures that modify the pointer
in compat_ptr(). Since HPET_INFO is the only one that
passes a pointer and that one is handled separately,
you should just drop the compat_ptr() conversion here.
Arnd