CVE-2021-47555 net: vlan: fix underflow for the real_dev refcnt
A refcount underflow in the Linux kernel VLAN driver can cause a memory leak and system hang, leading to denial of service.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2021-47555?
CVE-2021-47555 is a high-severity vulnerability in Linux kernel, published on 24 May 2024. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
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.
Weakness: CWE-191
Which versions are affected by CVE-2021-47555?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2021-47555?
Apply the vendor's patch.
Is CVE-2021-47555 being exploited?
There is no known exploitation of CVE-2021-47555 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as DEBIAN-CVE-2021-47555, UBUNTU-CVE-2021-47555.