On Tue, 18 Oct 2005 10:13:33 -0700, Greg KH <[email protected]> wrote:
> On Mon, Oct 17, 2005 at 06:15:54PM -0700, Pete Zaitcev wrote:
> > I'm cross-posting to l-k because someone I know was making sounds at
> > a notion of #ifdef CONFIG_COMPAT. But I think this solutions is superior
> > to adding anything outside of devio.c.
>
> Why not put this in fs/compat_ioctl.c where the other usbfs 32bit ioctls
> are?
This is what Dell people did originally. Here is their code:
+static int do_usbdevfs_ioctl(unsigned int fd, unsigned int cmd, unsigned long arg)
+{
+ struct usbdevfs_ioctl kioc;
+ struct usbdevfs_ioctl32 __user *uioc;
+ mm_segment_t old_fs;
+ u32 udata;
+ int err;
+
+ uioc = compat_ptr(arg);
+ if (get_user(kioc.ifno, &uioc->ifno) ||
+ get_user(kioc.ioctl_code, &uioc->ioctl_code) ||
+ __get_user(udata, &uioc->data))
+ return -EFAULT;
+
+ kioc.data = compat_ptr(udata);
+
+ old_fs = get_fs();
+ set_fs(KERNEL_DS);
+ err = sys_ioctl(fd, USBDEVFS_IOCTL, (unsigned long)&kioc);
+ set_fs(old_fs);
+
+ return err;
+}
The problem here is that compat_ptr does NOT turn user data pointer
into a kernel pointer. It's still a user pointer, only sized
differently. So, when you do set_fs(KERNEL_DS), this pointer
is invalid (miraclously, it does work on AMD64, so Dell's tests
pass on their new Xeons).
So, you cannot simply to have a small shim. Instead, you have to allocate
the buffer, do copy_from_user(), and then call the ioctl. But then,
it would be a double-copy, when the ioctl allocates the buffer again.
I tweaked this in various ways, and the patch I posted looks like
the cleanest solution. But please tell me if I miss something obvious.
-- Pete
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