CVE-2021-47555 Affecting kernel-livepatch-5_14_21-150500_55_68-default package, versions <1-150500.11.3.1


Severity

Recommended
0.0
medium
0
10

Based on SUSE Linux Enterprise Server security rating.

Threat Intelligence

EPSS
0.05% (18th percentile)

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  • Snyk IDSNYK-SLES155-KERNELLIVEPATCH514211505005568DEFAULT-7381175
  • published26 Jun 2024
  • disclosed25 Jun 2024

Introduced: 25 Jun 2024

CVE-2021-47555  (opens in a new tab)

How to fix?

Upgrade SLES:15.5 kernel-livepatch-5_14_21-150500_55_68-default to version 1-150500.11.3.1 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream kernel-livepatch-5_14_21-150500_55_68-default package and not the kernel-livepatch-5_14_21-150500_55_68-default package as distributed by SLES. See How to fix? for SLES:15.5 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