CVE-2021-47280

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.

• linux linux kernel (< 4.14.237) • linux linux kernel (>= 4.15 < 4.19.195) • linux linux kernel (>= 4.20 < 5.4.126) • linux linux kernel (>= 5.5 < 5.10.44) • linux linux kernel (>= 5.11 < 5.12.11) • linux linux kernel 5.13