CVE-2026-31607

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

usbip: validate numberofpackets in usbippackret_submit()

When a USB/IP client receives a RET_SUBMIT response,

usbippackret_submit() unconditionally overwrites

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

subsequently used as the loop bound in usbiprecviso() and

usbippadiso() to iterate over urb->isoframedesc[], a flexible

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

original numberofpackets from the CMD_SUBMIT.

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

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

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

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

KASAN confirmed this with kernel 7.0.0-rc5:

  BUG: KASAN: slab-out-of-bounds in usbiprecviso+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 (stubrx.c) and gadget side (vudcrx.c) already

validate numberofpackets in the CMD_SUBMIT path since commits

c6688ef9f297 ("usbip: fix stubrx: harden CMDSUBMIT path to handle

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

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

against USBIPMAXISO_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 numberofpackets.

This mirrors the existing validation of actual_length against

transferbufferlength in usbiprecvxbuff(), which checks the

response value against the original allocation size.

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

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

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

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

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

USBIPMAXISO_PACKETS limit.

Fix this by checking rpdu->numberofpackets against

urb->numberofpackets in usbippackret_submit() before the

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

usbippadiso() safely return early.