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Subject: [Bug 219525] Multiple bugs in mpr ioctl handler
Date: Tue, 30 May 2017 20:27:13 +0000
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D219525

--- Comment #2 from CTurt <ecturt@gmail.com> ---
Thanks for taking a look.

To clarify the point you asked about:

`recorded_events` is a fixed size, it looks like this in `struct mpr_softc`:

mpr_event_entry_t               recorded_events[MPR_EVENT_QUEUE_SIZE];

The kernel should copy out only `sizeof(sc->recored_events)` bytes at most =
from
here, or else it will copy out of bounds memory to userland.

Going back to the code:

        size =3D data->Size;
        if ((size >=3D sizeof(sc->recorded_events)) && (status =3D=3D 0)) {
            mpr_unlock(sc);
            if (copyout((void *)sc->recorded_events,
                PTRIN(data->PtrEvents), size) !=3D 0)
                status =3D EFAULT;
            mpr_lock(sc);
        }

Notice that it passes `size` to `copyout`, which can be greater than
`sizeof(sc->recorded_events)` (see the check).

Instead, the `copyout` call should be passed `sizeof(sc->recorded_events)` =
so
that it won't read more than the array contains.

So, you are correct when you say that it "is just checking if the user supp=
lied
size is enough to hold sizeof(sc->recored_events)". But this check won't
prevent copying out of bounds memory to userland.

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