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Hey everyone, in today's post, we will discuss a use-after-free vulnerability discovered in the siano smsusb module of the Linux kernel, which has been tagged with the CVE identifier CVE-2023-4132. This critical vulnerability can be exploited by a local user to crash the system, leading to a denial of service condition. Before diving into the details, let's first understand the basics of this vulnerability.

What is a Use-After-Free Vulnerability?

A "use-after-free" vulnerability is a type of security bug that occurs when a program continues to use memory after it has been freed or released. This can lead to crashes, random code execution, or information leaks, depending on the circumstances. In this case, the vulnerability affects the siano smsusb module in the Linux kernel.

The Impact of CVE-2023-4132

The vulnerability in the siano smsusb module allows a local user to trigger a denial of service condition by crashing the system. This can have serious implications if an attacker can gain access to a user's system and exploit this flaw, such as causing downtime for businesses and posing security risks to sensitive data. It's crucial to understand and patch this vulnerability to prevent exploitation.

Understanding the Root Cause

The bug in question occurs during device initialization when a siano device (a mobile digital TV receiver) is plugged into the system. A code snippet demonstrating the vulnerable part of the code can be seen below:

static int smsusb_probe(struct usb_interface *intf,
             const struct usb_device_id *id)
{
	struct smsusb_device_t *pdev;
	int rc;

	pdev = kzalloc(sizeof(struct smsusb_device_t), GFP_KERNEL);
	if (!pdev)
		return -ENOMEM;
	/* ... */

	rc = smscore_start_device(pdev->coredev);
	if (rc < )
		goto err_core_release;

	/* ... */
err_core_release:
	smscore_unregister_device(pdev->coredev);
error_coredev_alloc:
	kfree(pdev);
	return rc;
}

As you can see from the code snippet above, the use-after-free vulnerability stems from the fact that

smscore_unregister_device()

frees the

pdev->coredev

memory. However, in the error handling path (under the

err_core_release

label), the code still proceeds to access this freed memory, causing the use-after-free bug.

Mitigation and Patch Details

To mitigate this vulnerability, the following patch has been proposed and integrated into the upstream Linux kernel:

--- a/siano_probe
+++ b/siano_probe_fixed
@@ -20,8 +20,10 @@
 	err_core_release:
 		smscore_unregister_device(pdev->coredev);
 	error_coredev_alloc:
-		kfree(pdev);
 		return rc;
}

The patch removes the lines that free the

pdev

memory, thus addressing the use-after-free issue.

- Original advisory: https://seclists.org/oss-sec/2023/q2/13
- CVE Details: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-4132
- Linux kernel repository: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/

Conclusion

In this post, we discussed the critical use-after-free vulnerability found in the siano smsusb module of the Linux kernel, tagged as CVE-2023-4132. It's crucial to ensure that your Linux systems are updated to the latest kernel version to safeguard against this vulnerability. Stay informed about such security bugs and apply patches promptly to maintain a secure environment.

Timeline

Published on: 08/03/2023 15:15:00 UTC
Last modified on: 09/10/2023 12:16:00 UTC