Unity Linux 20.1070e Security Update: kernel (UTSA-2025-986913)

high Nessus Plugin ID 268096

Synopsis

The Unity Linux host is missing one or more security updates.

Description

The Unity Linux 20 host has a package installed that is affected by a vulnerability as referenced in the UTSA-2025-986913 advisory.

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

USB: core: Fix hang in usb_kill_urb by adding memory barriers

The syzbot fuzzer has identified a bug in which processes hang waiting for usb_kill_urb() to return. It turns out the issue is not unlinking the URB; that works just fine. Rather, the problem arises when the wakeup notification that the URB has completed is not received.

The reason is memory-access ordering on SMP systems. In outline form, usb_kill_urb() and __usb_hcd_giveback_urb() operating concurrently on different CPUs perform the following actions:

CPU 0 CPU 1
---------------------------- --------------------------------- usb_kill_urb(): __usb_hcd_giveback_urb():
... ...
atomic_inc(&urb->reject); atomic_dec(&urb->use_count);
... ...
wait_event(usb_kill_urb_queue, atomic_read(&urb->use_count) == 0);
if (atomic_read(&urb->reject)) wake_up(&usb_kill_urb_queue);

Confining your attention to urb->reject and urb->use_count, you can see that the overall pattern of accesses on CPU 0 is:

write urb->reject, then read urb->use_count;

whereas the overall pattern of accesses on CPU 1 is:

write urb->use_count, then read urb->reject.

This pattern is referred to in memory-model circles as SB (for Store Buffering), and it is well known that without suitable enforcement of the desired order of accesses -- in the form of memory barriers -- it is entirely possible for one or both CPUs to execute their reads ahead of their writes. The end result will be that sometimes CPU 0 sees the old un-decremented value of urb->use_count while CPU 1 sees the old un-incremented value of urb->reject. Consequently CPU 0 ends up on the wait queue and never gets woken up, leading to the observed hang in usb_kill_urb().

The same pattern of accesses occurs in usb_poison_urb() and the failure pathway of usb_hcd_submit_urb().

The problem is fixed by adding suitable memory barriers. To provide proper memory-access ordering in the SB pattern, a full barrier is required on both CPUs. The atomic_inc() and atomic_dec() accesses themselves don't provide any memory ordering, but since they are present, we can use the optimized smp_mb__after_atomic() memory barrier in the various routines to obtain the desired effect.

This patch adds the necessary memory barriers.

Tenable has extracted the preceding description block directly from the Unity Linux security advisory.

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

Plugin Details

Severity: High

ID: 268096

File Name: unity_linux_UTSA-2025-986913.nasl

Version: 1.1

Type: local

Family: Unity Linux Local Security Checks

Published: 10/7/2025

Updated: 10/7/2025

Supported Sensors: Nessus

Risk Information

VPR

Risk Factor: Medium

Score: 6.0

CVSS v2

Risk Factor: Medium

Base Score: 6.2

Temporal Score: 4.6

Vector: CVSS2#AV:L/AC:L/Au:S/C:C/I:N/A:C

CVSS Score Source: CVE-2022-48760

CVSS v3

Risk Factor: High

Base Score: 7.1

Temporal Score: 6.2

Vector: CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H

Temporal Vector: CVSS:3.0/E:U/RL:O/RC:C

Vulnerability Information

Required KB Items: Host/local_checks_enabled, Host/cpu, Host/UOS-Server/release, Host/UOS-Server/rpm-list

Exploit Ease: No known exploits are available

Patch Publication Date: 9/23/2025

Vulnerability Publication Date: 3/8/2022

Reference Information

CVE: CVE-2022-48760

Detections

Analytics