A recently identified vulnerability in the Linux kernel (CVE-2021-47017) can cause significant security issues if left unaddressed. The issue lies within the ath10k_htc_send_bundle function, where a use after free error occurs. This post will provide an in-depth explanation of the vulnerability, the associated code snippets, relevant links to original references, and exploit details.

Vulnerability Analysis

In a nutshell, the vulnerability (CVE-2021-47017) resides in the ath10k_htc_send_bundle function, specifically in the use of bundle_skb after it has been freed by dev_kfree_skb_any(bundle_skb). This can lead to unintended consequences as the freed memory could be used or accessed by other processes.

The issue lies in this particular code snippet

if (send_barrier) {
    skb_pull(bundle_skb, sizeof(struct ath10k_htc_hdr));
    status = ath10k_sdio_mbox_send_bundle(ar_sdio->ar,
                    skb->queue_mapping,
                    &bundle_skb, 1,
                    bundle_skb->len);
    dev_kfree_skb_any(bundle_skb);
}

In this snippet, bundle_skb is being freed through dev_kfree_skb_any(bundle_skb), yet it is still being used later in the code by bundle_skb->len. This results in the use of freed memory, which is a significant security vulnerability.

Proposed Patch

To resolve this issue, the patch replaces the use of bundle_skb->len with skb_len after the free operation is performed on bundle_skb. The updated code snippet is as follows:

if (send_barrier) {
    skb_pull(bundle_skb, sizeof(struct ath10k_htc_hdr));
    skb_len = bundle_skb->len; // Added to store the length of bundle_skb before it is freed
    status = ath10k_sdio_mbox_send_bundle(ar_sdio->ar,
                    skb->queue_mapping,
                    &bundle_skb, 1,
                    skb_len); // bundle_skb->len is replaced by skb_len
    dev_kfree_skb_any(bundle_skb);
}

By applying this patch, the use after free vulnerability is effectively mitigated, resulting in a more secure Linux kernel.

1. Linux Kernel Mailing List (LKML) - Patch Submission: https://lkml.org/lkml/2021/9/29/1621
2. Common Vulnerabilities and Exposures (CVE) Details: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-47017

Exploit Details

As of now, there are no known exploits that specifically target CVE-2021-47017. However, use after free vulnerabilities can generally lead to multiple types of attacks, including information disclosure, arbitrary code execution, or denial of service (DoS) attacks. Attackers can potentially use these vulnerabilities to gain unauthorized access to sensitive information in the kernel or execute malicious code.

It is highly recommended to apply the proposed patch if you are using the Linux kernel version containing this vulnerability, to safeguard your systems from potential threats.

Conclusion

CVE-2021-47017 is a serious vulnerability in the Linux kernel that can lead to various security risks. By understanding the issue and applying the necessary patch, system administrators and developers can ensure their systems are protected against this vulnerability. Stay vigilant and keep your kernel up-to-date to maintain secure systems.

Timeline

Published on: 02/28/2024 09:15:38 UTC
Last modified on: 05/29/2024 05:00:36 UTC