CVE-2021-47280: drm: Fix use-after-free read in drm_getunique()

Severity: high (CVSS 7.0 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2024-05-21 · updated 2026-06-17
Weakness: CWE-367

Description

In the Linux kernel, the following vulnerability has been resolved: drm: Fix use-after-free read in drm_getunique() There is a time-of-check-to-time-of-use error in drm_getunique() due to retrieving file_priv->master prior to locking the device's master mutex. An example can be seen in the crash report of the use-after-free error found by Syzbot: https://syzkaller.appspot.com/bug?id=148d2f1dfac64af52ffd27b661981a540724f803 In the report, the master pointer was used after being freed. This is because another process had acquired the device's master mutex in drm_setmaster_ioctl(), then overwrote fpriv->master in drm_new_set_master(). The old value of fpriv->master was subsequently freed before the mutex was unlocked. To fix this, we lock the device's master mutex before retrieving the pointer from from fpriv->master. This patch passes the Syzbot reproducer test.

Affected products

Linux kernel: before 4.14.237; from 4.15 before 4.19.195; from 4.20 before 5.4.126; from 5.5 before 5.10.44; from 5.11 before 5.12.11; 5.13-rc1, 5.13-rc2, 5.13-rc3, 5.13-rc4, 5.13-rc5 — fixed in 4.14.237, 4.19.195, 5.10.44, 5.12.11, 5.4.126

How to fix

Upgrade to a fixed version: Linux kernel 4.14.237, 4.19.195, 5.10.44, 5.12.11. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2021-47280 or the next vulnerability affects your stack