CVE-2023-52652 - A Close Look at the Linux Kernel NTB Name Leak Vulnerability

The Linux kernel recently patched a bug tracked as CVE-2023-52652 that specifically affected the Non-Transparent Bridge (NTB) subsystem. This vulnerability could lead to a memory leak involving device names under rare error conditions when registering NTB devices.

In this exclusive deep-dive, we'll break down what caused the bug, review the real code changes, show how it could be triggered, and provide essential references.

What Is NTB?

NTB stands for Non-Transparent Bridge. It's a hardware feature often found in server-class CPUs that enables communication between two separate PCI Express domains. The Linux kernel has a subsystem that manages NTB devices, providing necessary abstractions for modules or applications that use them.

What Happened?

When registering a new NTB device in the kernel, the function ntb_register_device() is called. This function sets the device name using dev_set_name() and then tries to register the device with device_register().

If device_register() fails, the device name allocated earlier by dev_set_name() is left in memory - because the required cleanup is not performed. Over time, repeated failures could cause a memory leak.

Excerpt from the Kernel Patch Commit

> If device_register() fails in ntb_register_device(), the device name allocated by dev_set_name() should be freed. As per the comment in device_register(), callers should use put_device() to give up the reference in the error path. So fix this by calling put_device() in the error path so that the name can be freed in kobject_cleanup().

Why Is This a Problem?

Modern systems may have monitoring or drivers that constantly add/remove devices programmatically. If this code path gets hit repeatedly, it can steadily consume kernel memory with unreleased device names, potentially leading to degraded system performance or, in some cases, denial-of-service.

Before Patch

int ntb_register_device(struct ntb_dev *ntb, const char *name)
{
    int ret;
    dev_set_name(&ntb->dev, "%s", name);
    ret = device_register(&ntb->dev);
    if (ret)
        return ret; // <-- memory leak if device_register fails
    return ;
}

In this form, if device_register() fails, the device name allocated by dev_set_name() is not freed.

After Patch (Fixed)

int ntb_register_device(struct ntb_dev *ntb, const char *name)
{
    int ret;
    dev_set_name(&ntb->dev, "%s", name);
    ret = device_register(&ntb->dev);
    if (ret) {
        put_device(&ntb->dev); // <-- Cleanup happens here!
        return ret;
    }
    return ;
}

The fix is simple: put_device() is called in the error path, ensuring all associated memory (including the dynamically allocated device name) is freed properly via kobject_cleanup().

Triggering the Bug

While this vulnerability isn't directly exploitable for elevation of privileges or running arbitrary code, it can be triggered by anyone with a way to repeatedly register and unregister NTB devices—such as a privileged user loading buggy NTB drivers.

Proof-of-Concept Pseudocode

struct ntb_dev test_ntb;

for (int i = ; i < 10000; i++) {
    // Assume device_register fails (simulate an error)
    ntb_register_device(&test_ntb, "leaky_device");
}

Above: If device_register() fails each time, each call would cause a name memory leak before the patch. After the patch, memory is properly released.

Class: Memory Leak, Denial-of-Service (DoS) (if attacked persistently)

- Attack Surface: Local (requires root or equivalent to load drivers / allocate devices)

Severity: LOW (but worth patching)

This is not a remote or privilege-escalation bug but could theoretically allow a local attacker to degrade system resources by continuously hitting this path.

Conclusion

CVE-2023-52652 serves as a reminder that even small memory management issues in low-level subsystems like Linux's NTB can have security and stability consequences. If you maintain systems using NTB or build kernel modules that interface with it, make sure you're running a patched kernel version that includes this commit or later.

Stay updated—and as always, review kernel patches and security advisories regularly.

Timeline

Published on: 05/01/2024 13:15:48 UTC
Last modified on: 05/04/2025 07:40:53 UTC