// For flags

CVE-2021-47555

net: vlan: fix underflow for the real_dev refcnt

Severity Score

4.4
*CVSS v3.1

Exploit Likelihood

*EPSS

Affected Versions

*CPE

Public Exploits

0
*Multiple Sources

Exploited in Wild

-
*KEV

Decision

Track
*SSVC
Descriptions

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.

En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: net: vlan: corrige el desbordamiento insuficiente para real_dev refcnt Inyecte el error antes de dev_hold(real_dev) en Register_vlan_dev() y ejecute el siguiente caso de prueba: ip link add dev dummy1 tipo dummy ip link add nombre dummy1.100 link dummy1 tipo vlan id 100 ip link del dev dummy1 Cuando se elimina el dispositivo de red ficticio, recibiremos una ADVERTENCIA como la siguiente: ===================== ==================================================== = refcount_t: decremento hit 0; pérdida de memoria. ADVERTENCIA: CPU: 2 PID: 0 en lib/refcount.c:31 refcount_warn_saturate+0xbf/0x1e0 y un bucle sin fin de: ======================== ================================================= unregister_netdevice: esperando que el dummy1 quede libre. Recuento de uso = -1073741824 Esto se debe a que dev_put(real_dev) en vlan_dev_free() se llama sin dev_hold(real_dev) en Register_vlan_dev(). Hace que el refcnt de real_dev se desborde. Mueva dev_hold(real_dev) a vlan_dev_init() que es la devolución de llamada de ndo_init(). Eso hace que dev_hold() y dev_put() para real_dev de vlan sean simétricos.

*Credits: N/A
CVSS Scores
Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
None
Availability
Low
* Common Vulnerability Scoring System
SSVC
  • Decision:Track
Exploitation
None
Automatable
No
Tech. Impact
Partial
* Organization's Worst-case Scenario
Timeline
  • 2024-05-24 CVE Reserved
  • 2024-05-24 CVE Published
  • 2024-05-25 EPSS Updated
  • 2024-12-19 CVE Updated
  • ---------- Exploited in Wild
  • ---------- KEV Due Date
  • ---------- First Exploit
CWE
CAPEC
Affected Vendors, Products, and Versions
Vendor Product Version Other Status
Vendor Product Version Other Status <-- --> Vendor Product Version Other Status
Linux
Search vendor "Linux"
 Linux Kernel
Search vendor "Linux" for product "Linux Kernel"
 >= 5.4.160 < 5.4.163
Search vendor "Linux" for product "Linux Kernel" and version " >= 5.4.160 < 5.4.163"
en
Affected
Linux
Search vendor "Linux"
 Linux Kernel
Search vendor "Linux" for product "Linux Kernel"
 >= 5.10.80 < 5.10.83
Search vendor "Linux" for product "Linux Kernel" and version " >= 5.10.80 < 5.10.83"
en
Affected
Linux
Search vendor "Linux"
 Linux Kernel
Search vendor "Linux" for product "Linux Kernel"
 >= 5.15.3 < 5.15.6
Search vendor "Linux" for product "Linux Kernel" and version " >= 5.15.3 < 5.15.6"
en
Affected
Linux
Search vendor "Linux"
 Linux Kernel
Search vendor "Linux" for product "Linux Kernel"
 5.14.19
Search vendor "Linux" for product "Linux Kernel" and version "5.14.19"
en
Affected