On Thu, Mar 18, 2021 at 5:13 PM Alessio Balsini <balsini@xxxxxxxxxxx> wrote:
> On Tue, Mar 16, 2021 at 07:53:06PM +0100, Arnd Bergmann wrote:
> > On Mon, Jan 25, 2021 at 4:48 PM Alessio Balsini <balsini@xxxxxxxxxxx> wrote:
> > >
>
> Thanks for spotting this possible criticality.
>
> I noticed that 32-bit users pace was unable to use the
> FUSE_DEV_IOC_CLONE ioctl on 64-bit kernels, so this change avoid this
> issue by forcing the kernel to interpret 32 and 64 bit
> FUSE_DEV_IOC_CLONE command as if they were the same.
As far as I can tell from the kernel headers, the command code should
be the same for both 32-bit and 64-bit tasks: 0x8004e500.
Can you find out what exact value you see in the user space that was
causing problems, and how it ended up with a different value than
the 64-bit version?
If there are two possible command codes, I'd suggest you just change
the driver to handle both variants explicitly, but not any other one.
> This is the simplest solution I could find as the UAPI is not changed
> as, as you mentioned, the argument doesn't require any conversion.
>
> I understand that this might limit possible future extensions of the
> FUSE_DEV_IOC_XXX ioctls if their in/out argument changed depending on
> the architecture, but only at that point we can switch to using the
> compat layer, right?
>
> What I'm worried about is the direction, do you think this would be an
> issue?
>
> I can start working on a compat layer fix meanwhile.
For a proper well-designed ioctl interface, compat support should not
need anything beyond the '.compat_ioctl = compat_ptr_ioctl'
assignment.
Arnd
