CVE-2021-46904: net: hso: fix null-ptr-deref during tty device unregistration

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2024-02-26 · updated 2026-06-17
Weakness: CWE-476

Description

In the Linux kernel, the following vulnerability has been resolved: net: hso: fix null-ptr-deref during tty device unregistration Multiple ttys try to claim the same the minor number causing a double unregistration of the same device. The first unregistration succeeds but the next one results in a null-ptr-deref. The get_free_serial_index() function returns an available minor number but doesn't assign it immediately. The assignment is done by the caller later. But before this assignment, calls to get_free_serial_index() would return the same minor number. Fix this by modifying get_free_serial_index to assign the minor number immediately after one is found to be and rename it to obtain_minor() to better reflect what it does. Similary, rename set_serial_by_index() to release_minor() and modify it to free up the minor number of the given hso_serial. Every obtain_minor() should have corresponding release_minor() call.

Affected products

Linux kernel: from 2.6.27 before 4.4.268; from 4.5.0 before 4.9.268; from 4.10.0 before 4.14.232; from 4.15.0 before 4.19.187; from 4.20.0 before 5.4.112; from 5.5.0 before 5.10.30 — fixed in 4.14.232, 4.19.187, 4.4.268, 4.9.268, 5.10.30, 5.11.14

How to fix

Upgrade to a fixed version: Linux kernel 4.14.232, 4.19.187, 4.4.268, 4.9.268. Check the vendor advisory for mitigations.

References

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