Qualcomm Snapdragon chips are used in millions of smartphones, IoT devices, automotive systems, and more. Security vulnerabilities affecting these widely-deployed platforms can have serious effects on users and vendors. Today, we'll explore CVE-2022-22057 — a use-after-free bug caused by a race condition in the graphics fence subsystem of various Snapdragon processors.

> This article provides an exclusive, accessible breakdown, complete with code-inspired snippets, links for further reading, and detailed steps on how one might exploit this flaw.

What is CVE-2022-22057?

CVE-2022-22057 is a security vulnerability in Qualcomm Snapdragon chips' graphics stack. It involves a race condition when a *fence file descriptor* is closed at the same time as the associated *graphics timeline* is destroyed. The flaw lies in how certain resources are managed and freed, leading to a use-after-free state.

A successful attack could let an unprivileged user or a malicious app potentially cause a device to crash, escalate privileges, or even run arbitrary code in the context of the graphics driver — a major risk.

Understanding the Fence Mechanism

In graphics programming, a *fence* is a synchronization primitive — it's like a traffic signal for commands sent to the GPU. Each fence has a *timeline*, controlling the sequence of operations.

File Descriptors (FDs) are used to represent fences in user space, and when you close an FD, the kernel typically destroys the timeline if there are no more users.

User Thread B: Destroys the timeline (destroy_timeline()).

If these happen at just the wrong moment — say, Thread A is freeing memory while Thread B is still using it — you get a *use-after-free* bug.

Let's simplify what might be happening under the hood

void close_fence_fd(int fd) {
    timeline = fd_to_timeline(fd);
    ref_dec(timeline);
    if (timeline->refcount == ) {
        free(timeline);
    }
}

void destroy_timeline(timeline_t* timeline) {
    // -- This could get called in another context --
    perform_cleanup(timeline);
    free(timeline);
}

If both close_fence_fd() and destroy_timeline() run almost simultaneously, both may try to destroy the same timeline object — causing use-after-free.

How an Attacker Could Exploit It

The conditions for exploitation are realistic, especially for a determined attacker or a malicious app with access to the graphic subsystem.

Use-After-Free: With great timing, Thread 1 frees the timeline while Thread 2 is still using it.

3. Hijack Freed Memory: As soon as the timeline is freed, allocate data controlled by the attacker to occupy that space.

4. Arbitrary Code Execution: Depending on how the stale pointer is dereferenced, attacker data can be interpreted as valid objects or code.

Real-World Impact

In the worst-case scenario, an attacker could run code as "system" or "graphics" user, bypassing normal Android sandboxing. Even if only a crash is triggered, it could lead to denial of service, freezing or rebooting critical automotive (Snapdragon Auto), IoT, or mobile devices.

References & Further Reading

- Qualcomm Product Security Bulletin: May 2022
- CVE-2022-22057 in NVD
- Linux Kernel: Use-After-Free Exploit Techniques
- Android Security Bulletin: July 2022

How It Was Fixed

Qualcomm addressed this vulnerability by adding proper locking and reference counting to make sure that:

A timeline can't be destroyed while it's still in use by any fence FD;

- Freeing any shared memory objects now involves stricter synchronization so they can't be double-freed or used after they're invalid.

If you’re a vendor, apply the latest Qualcomm BSP patches and ensure you’re shipping updated firmware. If you’re a user, keep your device up-to-date with the latest security patches from your manufacturer.

Conclusion

CVE-2022-22057 is a serious vulnerability rooted in complex race conditions and memory management failures — a reminder that even minor flaws in kernel-level code can have major consequences. Keeping devices updated and encouraging responsible disclosure helps protect the millions of people depending on Snapdragon-powered gadgets daily.

Stay safe, and always patch your devices!

*This article is an exclusive, easy-to-read breakdown for educational and awareness purposes. If you think your device could be affected, check with your vendor and update as soon as possible!*

Timeline

Published on: 06/14/2022 10:15:00 UTC
Last modified on: 06/22/2022 14:50:00 UTC