CVE-2026-31607

In the Linux kernel, the following vulnerability has been resolved:

usbip: validate number_of_packets in usbip_pack_ret_submit()

When a USB/IP client receives a RET_SUBMIT response,

usbip_pack_ret_submit() unconditionally overwrites

urb->number_of_packets from the network PDU. This value is

subsequently used as the loop bound in usbip_recv_iso() and

usbip_pad_iso() to iterate over urb->iso_frame_desc[], a flexible

array whose size was fixed at URB allocation time based on the

*original* number_of_packets from the CMD_SUBMIT.

A malicious USB/IP server can set number_of_packets in the response

to a value larger than what was originally submitted, causing a heap

out-of-bounds write when usbip_recv_iso() writes to

urb->iso_frame_desc[i] beyond the allocated region.

KASAN confirmed this with kernel 7.0.0-rc5:

BUG: KASAN: slab-out-of-bounds in usbip_recv_iso+0x46a/0x640

Write of size 4 at addr ffff888106351d40 by task vhci_rx/69

The buggy address is located 0 bytes to the right of

allocated 320-byte region [ffff888106351c00, ffff888106351d40)

The server side (stub_rx.c) and gadget side (vudc_rx.c) already

validate number_of_packets in the CMD_SUBMIT path since commits

c6688ef9f297 ("usbip: fix stub_rx: harden CMD_SUBMIT path to handle

malicious input") and b78d830f0049 ("usbip: fix vudc_rx: harden

CMD_SUBMIT path to handle malicious input"). The server side validates

against USBIP_MAX_ISO_PACKETS because no URB exists yet at that point.

On the client side we have the original URB, so we can use the tighter

bound: the response must not exceed the original number_of_packets.

This mirrors the existing validation of actual_length against

transfer_buffer_length in usbip_recv_xbuff(), which checks the

response value against the original allocation size.

Kelvin Mbogo's series ("usb: usbip: fix integer overflow in

usbip_recv_iso()", v2) hardens the receive-side functions themselves;

this patch complements that work by catching the bad value at its

source -- in usbip_pack_ret_submit() before the overwrite -- and

using the tighter per-URB allocation bound rather than the global

USBIP_MAX_ISO_PACKETS limit.

Fix this by checking rpdu->number_of_packets against

urb->number_of_packets in usbip_pack_ret_submit() before the

overwrite. On violation, clamp to zero so that usbip_recv_iso() and

usbip_pad_iso() safely return early.