The Linux kernel, which is an open-source operating system widely used worldwide, has recently resolved a critical vulnerability in its Bluetooth subsystem. The vulnerability, designated as CVE-2024-26889, existed within the Bluetooth: hci_core module and could allow attackers to exploit a buffer overflow issue potentially. In this blog post, we will dive into the details of the vulnerability, analyze a code snippet and demonstrate the provided solution, as well as discuss the importance of staying up-to-date with security patches.

Vulnerability Details

The vulnerability in question can be found in the Bluetooth: hci_core module of the Linux kernel. It is related to an unsafe memory copying operation on a fixed-size field within the hci_dev_info structure. This issue occurs when the hdev->name value is larger than the fixed-size name[8] field, causing the strcpy function to attempt to write past its boundaries. This improper memory handling could potentially lead to a buffer overflow, allowing attackers to exploit the vulnerability for malicious purposes such as code execution or denial of service attacks.

Code Snippet with Vulnerability

The vulnerable code is located within the hci_core.c file, which is part of the Linux kernel repository. Below is an excerpt of the code containing the vulnerability:

/* hci_core.c - HCI core handling */

struct hci_dev_info {
…
	char name[8];
…
};
…
static void hci_rename_work(struct work_struct *work)
{
	struct hci_dev *hdev = container_of(work, struct hci_dev, rename);
…
	strcpy(info->name, hdev->name);
…
}

As the code snippet demonstrates, the hci_dev_info structure contains a fixed-size name[8] field. The issue arises when using strcpy to copy the hdev->name value to the info->name field without checking the size of the source string.

Solution and Patch

To resolve the vulnerability, the recommended solution is to switch from using strcpy to a safer alternative, strscpy. The strscpy function ensures that any memory copying operation does not exceed the size of the destination buffer, thus eliminating the possibility of a buffer overflow issue. The patched code is provided below:

/* hci_core.c - HCI core handling */

struct hci_dev_info {
…
	char name[8];
…
};
…
static void hci_rename_work(struct work_struct *work)
{
	struct hci_dev *hdev = container_of(work, struct hci_dev, rename);
…
	strscpy(info->name, hdev->name, sizeof(info->name));
…
}

By switching from strcpy to strscpy, the fixed-size name[8] field within the hci_dev_info structure remains protected from potential buffer overflow exploits.

Original References

The Linux kernel repository, containing all source code including hci_core.c, can be found here: https://github.com/torvalds/linux

The announcement for the vulnerability resolution is available at: https://git.kernel.org/pub/scm/linux/kernel/git/bluetooth/bluetooth-next.git/commit/?id=396b4a19573ecda5ab86ec35c9eb6a60386bf4

Conclusion

CVE-2024-26889 highlights the importance of maintaining the security of critical systems and components. As a widely used operating system, the Linux kernel should be updated regularly to protect against newly discovered vulnerabilities. The Bluetooth: hci_core buffer overflow issue serves as a reminder to developers and system administrators to stay vigilant and patch their systems promptly.

Timeline

Published on: 04/17/2024 11:15:10 UTC
Last modified on: 10/31/2024 16:35:10 UTC