drm/virtio: bound EDID block reads to the response buffer

drm/virtio: bound EDID block reads to the response buffer

virtio_get_edid_block() validates the read offset only against the
device-supplied resp->size field, never against the fixed-size resp->edid
array. The EDID block index is driven by the device-supplied extension
count, so a malicious virtio-gpu backend can advertise a large size
together with a high block count and read far past the array into adjacent
kernel memory, which is then surfaced in the parsed EDID (an out-of-bounds
read / info leak).

Also reject any read whose end exceeds the size of the edid array.
Conforming EDID responses stay within the array and are unaffected.

Fixes: b4b01b4995fb ("drm/virtio: add edid support")
Cc: stable@vger.kernel.org
Signed-off-by: Bryam Vargas <hexlabsecurity@proton.me>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Link: https://patch.msgid.link/20260620-b4-disp-22bba7bf-v1-1-b95924cee742@proton.me