A use-after-free vulnerability has been discovered in Linux kernel versions before 5.19.2. Identified as CVE-2022-4095, this critical security flaw allows a local adversary to potentially launch a denial of service attack and even escalate their privileges on the affected system. In this detailed long-read post, we'll discuss the issue in-depth, provide code snippets, reference original sources, and examine the exploit details.

Vulnerability Details

The vulnerability in question has been found in the cmd_hdl_filter function in the file drivers/staging/rtl8712/rtl8712_cmd.c of the Linux kernel source code. It is a use-after-free bug that arises due to the incorrect handling of memory objects in the aforementioned function. The vulnerability could potentially lead to data corruption, crashing of the system, or unauthorized access for an attacker.

Let's take a look at the affected code snippet within the rtl8712_cmd.c file

static int cmd_hdl_filter(struct _adapter *padapter, struct cmd_obj *pcmd)
{
	...
	unsigned int cmdsz;
	...
	cmdsz = ALIGN_RND(sizeof(struct cmd_obj), 4) + pcmd->cmdsz;
	...
	pbuf = vmalloc(cmdsz);
	
	if (!pbuf)
		return H2C_PARAMETERS_ERROR;
	
	_memcpy(pbuf, pcmd, cmdsz);
	...
	rt_status = r8712_fw_cmd(padapter, (struct cmd_obj *)pbuf);
	...
	vfree(pbuf); // Incorrect memory handling here
	...
	return rt_status;
}

In the code snippet above, the cmdsz variable is used to calculate the size of the memory object that will be allocated using the vmalloc function. The allocated memory is then copied into the buffer pbuf. Afterward, the function r8712_fw_cmd is called, and when it returns, the vfree function is used to free the previously allocated memory.

The problem arises when vfree is called to release the memory occupied by the pbuf buffer. The code fails to ensure that no other pointers are still referencing the memory, leading to use-after-free vulnerability.

Original References

The Linux kernel team has acknowledged the vulnerability and provided a patch fixing the issue. The details of this patch can be found in the following commit history:

- Commit: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7c7bc34
- Patch file: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/patch/?id=7c7bc34

Exploit Details

An attacker with local access to an unpatched system can exploit this vulnerability by triggering the faulty code path in the cmd_hdl_filter function. The attacker can allocate a memory object, write malicious code into it, and then manipulate the system to execute the code after the memory is freed. This could result in the crashing of the system, causing a denial of service, or potential privilege escalation if the attacker can run their code with elevated privileges.

Remediation

To mitigate this vulnerability, users are advised to update their Linux kernel to version 5.19.2 or newer as soon as possible. The patch provided by the kernel team fixes the issue by properly handling the memory objects in the cmd_hdl_filter function, avoiding the use-after-free problem.

Conclusion

CVE-2022-4095 is a severe use-after-free vulnerability that affects Linux kernel versions before 5.19.2. With proper understanding and timely patching, users can protect their systems from potential security risks. By staying informed and vigilant regarding security updates, you ensure the safety and integrity of your systems and networks.

Timeline

Published on: 03/22/2023 15:15:00 UTC
Last modified on: 03/24/2023 20:43:00 UTC