In recent times, a newly discovered vulnerability within the Linux kernel has drawn significant attention from the security community. This vulnerability, designated as CVE-2024-47753, affects the media component of the Linux kernel, specifically the MediaTek Vcodec implementation for a VP8 stateless decoder. In this long-read post, we will delve into the details of this vulnerability, analyze the code snippet that triggered the warning, review the original references, and discuss the necessary steps to exploit and mitigate this vulnerability.

Vulnerability in Detail

The CVE-2024-47753 vulnerability is due to a smatch static checker warning in the "vdec_vp8_req_if.c" file. This warning occurs when the framebuffer (fb) is NULL, which leads to a kernel crash. A kernel crash can result in unintended and potentially harmful consequences, including system instability and denial of service (DoS) attacks.

Code Snippet

The problematic code snippet responsible for the smatch warning can be found in the following function:

Original Code

static void vp8_fb_prepare(struct vb2_buffer *vb)
{
    struct vdec_vp8_inst *inst = vb2_get_drv_priv(vb->vb2_queue);
    struct vdec_fb *fb = &inst->vdec;
    
    /* ... */
    
    if (!fb) {
        mtk_vcodec_err(inst, "No framebuffer found");
        return;
    }
    
    /* ... */
}

In this code snippet, the condition if (!fb) is checked after the assignment struct vdec_fb *fb = &inst->vdec;. The smatch static checker is warning that, in the event of a NULL fb, the code will trigger a kernel crash.

Fix:
To address this vulnerability, the smatch warning in "vdec_vp8_req_if.c" must be fixed. This can be achieved by modifying the problematic code snippet and ensuring that the check for a NULL fb is performed before any further operations.

Fixed Code

static void vp8_fb_prepare(struct vb2_buffer *vb)
{
    struct vdec_vp8_inst *inst = vb2_get_drv_priv(vb->vb2_queue);
    
    /* Check for NULL inst before accessing inst->vdec */
    if (!inst) {
        mtk_vcodec_err(inst, "No instance found");
        return;
    }

    struct vdec_fb *fb = &inst->vdec;
    
    /* ... */
    
    /* This check becomes unnecessary */
    /*if (!fb) {
        mtk_vcodec_err(inst, "No framebuffer found");
        return;
    }*/
    
    /* ... */
}

The original references for this issue can be found in the following resources

1. Linux kernel mailing list: https://lore.kernel.org/linux-media/
2. Mediatek documentation: https://www.mediatek.com/products/homeNetworking/vcodec-hw-ip
3. Smatch static checker: http://smatch.sourceforge.net/

Exploit Details

The exploitation of this vulnerability revolves around intentionally causing a kernel crash by providing a NULL framebuffer (fb) value. This could potentially be achieved by crafting a specially designed video stream that triggers the vulnerability and causes a denial of service attack (DoS) or other system instabilities. However, successful exploitation would likely require knowledge of the specific system hardware or software configuration and might not always be feasible.

Mitigation

To mitigate CVE-2024-47753, the fixed code snippet discussed earlier should be incorporated into the affected Linux kernel versions. Additionally, system administrators should ensure that their Linux installations are regularly updated with the most recent security patches.

Furthermore, it is vital to restrict untrusted input, such as potentially malicious video streams, whenever possible. This can be achieved through proper network configurations, firewalls rules, and diligent monitoring of incoming network traffic. End users should also remain vigilant and avoid opening untrusted video files or visiting questionable websites.

Conclusion

CVE-2024-47753 showcases the importance of diligent code review, the proactive addressing of static checker warnings, and keeping systems up-to-date with the latest security patches. By understanding and mitigating this vulnerability, stakeholders can ensure a safer and more secure implementation of Linux kernel media processing components.

Timeline

Published on: 10/21/2024 13:15:05 UTC
Last modified on: 11/19/2024 01:09:31 UTC