CVE-2023-31084

What it actually does

The vulnerability allows a blocking semaphore acquisition (down()) inside a wait_event_interruptible context in dvb_frontend_get_event, violating the requirement that the task remain in TASK_RUNNING and enabling a race that can deadlock the DVB frontend state machine.

Why it matters to the business

Linux systems handling digital video broadcast hardware may experience kernel-level hangs or reduced availability when media applications interact with the frontend driver, disrupting broadcast reception or streaming workloads.

How an attack unfolds

A local attacker with access to a DVB device opens the frontend, triggers event waits, and races the semaphore acquisition so that the process sleeps while holding state that prevents progress, causing the kernel thread or user process to block indefinitely.

How to fix it

Update the Linux kernel to a version containing commit b8c75e4a1b325ea0a9433fa8834be97b5836b946 or later; rebuild and reboot with the patched kernel. Where immediate patching is not possible, restrict unprivileged access to DVB device nodes via udev rules or device cgroup policies.

How to confirm the fix worked

Confirm the running kernel Git commit or version string contains b8c75e4a1b325ea0a9433fa8834be97b5836b946; attempt to reproduce the original wait_event and down sequence under controlled load to verify absence of deadlock.

Typical attack path

1. Obtain local user access on a Linux system with DVB frontend hardware or emulated device present.
2. Open /dev/dvb/adapterX/frontendY and issue ioctl or read operations that invoke dvb_frontend_get_event.
3. Trigger concurrent access to fepriv->sem while the wait_event condition evaluates false to force the blocking down() call.
4. Leave the task in a non-runnable state, resulting in deadlock or prolonged unresponsiveness of the DVB subsystem.

How to detect it

Review kernel logs for DVB frontend semaphore or wait_event warnings, and inspect process traces showing tasks stuck inside dvb_frontend_get_event or down() on fepriv->sem; correlate with application access to DVB device files.

What your security team should do

• Prioritize kernel updates on all systems exposing DVB or media devices within the next maintenance window.
• Audit local user permissions on /dev/dvb/* nodes and apply least-privilege device access controls.
• Monitor vendor advisories for backported fixes in distribution kernels and schedule deployment.