Improper Update of Reference Count Affecting kernel-firmware package, versions *


Severity

Recommended
low

Based on Red Hat Enterprise Linux security rating.

Threat Intelligence

EPSS
0.05% (18th percentile)

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  • Snyk IDSNYK-RHEL6-KERNELFIRMWARE-7125804
  • published27 May 2024
  • disclosed24 May 2024

Introduced: 24 May 2024

CVE-2021-47555  (opens in a new tab)
CWE-911  (opens in a new tab)
CWE-124  (opens in a new tab)

How to fix?

There is no fixed version for RHEL:6 kernel-firmware.

NVD Description

Note: Versions mentioned in the description apply only to the upstream kernel-firmware package and not the kernel-firmware package as distributed by RHEL. See How to fix? for RHEL:6 relevant fixed versions and status.

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

net: vlan: fix underflow for the real_dev refcnt

Inject error before dev_hold(real_dev) in register_vlan_dev(), and execute the following testcase:

ip link add dev dummy1 type dummy ip link add name dummy1.100 link dummy1 type vlan id 100 ip link del dev dummy1

When the dummy netdevice is removed, we will get a WARNING as following:

======================================================================= refcount_t: decrement hit 0; leaking memory. WARNING: CPU: 2 PID: 0 at lib/refcount.c:31 refcount_warn_saturate+0xbf/0x1e0

and an endless loop of:

======================================================================= unregister_netdevice: waiting for dummy1 to become free. Usage count = -1073741824

That is because dev_put(real_dev) in vlan_dev_free() be called without dev_hold(real_dev) in register_vlan_dev(). It makes the refcnt of real_dev underflow.

Move the dev_hold(real_dev) to vlan_dev_init() which is the call-back of ndo_init(). That makes dev_hold() and dev_put() for vlan's real_dev symmetrical.

CVSS Scores

version 3.1