usb: usbip: fix OOB read/write in usbip_pad_iso()

usb: usbip: fix OOB read/write in usbip_pad_iso()

usbip_pad_iso() repositions ISO frame data within the transfer buffer
via memmove().  Neither the source offset (actualoffset, derived by
subtracting wire-supplied actual_length values) nor the destination
offset (iso_frame_desc[i].offset, taken directly from the wire) is
bounds-checked.

If a crafted actual_length wraps actualoffset negative through the
subtraction (see patch 2/3 for the root cause), the memmove source
points before the allocation - slab OOB read, data returned to
userspace.

Independently, iso_frame_desc[i].offset is never validated against
transfer_buffer_length.  Setting offset past the end of the buffer
gives a fully controlled OOB write into whatever sits next in the
slab - confirmed with offset=400 on a 392-byte buffer, 64-byte write.

Add bounds checks for both the source and destination ranges before
each memmove call.  Use unsigned comparisons after the sign check on
actualoffset to avoid signed/unsigned conversion surprises.

Signed-off-by: Kelvin Mbogo <addcontent08@gmail.com>
Link: https://patch.msgid.link/20260325103640.8090-3-addcontent08@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>