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CVE-2021-47555
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MITRE ATT&CK
Collection
Command and Control
Credential Access
Defense Evasion
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Execution
Exfiltration
Impact
Initial Access
Lateral Movement
Persistence
Privilege Escalation
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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.
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- Linux
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