CVE-2021-47555: linux kernel Integer Underflow — Fix

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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CVSS v3.1 Score

5.5

MEDIUM

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Weakness Type (CWE)

CWE-191 CWE-191

Affected Products

Vendor	Product	Versions
linux	linux_kernel	5.4.160 — 5.4.163
linux	linux_kernel	5.10.80 — 5.10.83
linux	linux_kernel	5.14.19 — 5.15
linux	linux_kernel	5.15.3 — 5.15.6
linux	linux_kernel	All
linux	linux_kernel	All

References

Advisories & Patches

https://git.kernel.org/stable/c/01d9cc2dea3fde3bad6d27f464eff463496e2b00 https://git.kernel.org/stable/c/5e44178864b38dd70b877985abd7d86fdb95f27d https://git.kernel.org/stable/c/6e800ee43218a56acc93676bbb3d93b74779e555 https://git.kernel.org/stable/c/f7fc72a508cf115c273a7a29350069def1041890 https://git.kernel.org/stable/c/01d9cc2dea3fde3bad6d27f464eff463496e2b00 https://git.kernel.org/stable/c/5e44178864b38dd70b877985abd7d86fdb95f27d https://git.kernel.org/stable/c/6e800ee43218a56acc93676bbb3d93b74779e555 https://git.kernel.org/stable/c/f7fc72a508cf115c273a7a29350069def1041890

Frequently Asked Questions

What is CVE-2021-47555? +

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. It has a CVSS v3.1 base score of 5.5 (MEDIUM).

How severe is CVE-2021-47555? +

CVE-2021-47555 has a CVSS v3.1 score of 5.5 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance.

What products are affected by CVE-2021-47555? +

CVE-2021-47555 affects products from linux, specifically: linux_kernel. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2021-47555? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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