In May 2022, security researchers discovered a critical vulnerability in the Linux kernel’s NFC Marvell (nfcmrvl) driver, assigned as CVE-2022-1734. This vulnerability stems from a race condition that could let attackers exploit a _use-after-free_ bug when the driver’s cleanup process interferes with the firmware download routine due to missing synchronization. In this post, we’ll break down CVE-2022-1734, show you what this bug looks like in the code, explain how it can be exploited, and provide resources for further learning.

What is CVE-2022-1734?

CVE-2022-1734 is a critical bug in the Linux kernel, specifically in the _nfcmrvl_ NFC device driver (found in drivers/nfc/nfcmrvl/main.c). The flaw can happen when the device cleanup routine (nfcmrvl_nci_unregister_dev) doesn’t properly synchronize with the firmware download process. This can result in the driver trying to access a memory region (struct) that has already been freed—a classic _use-after-free_ error.

Impact:
Malicious users (even those running as normal user, if they could trigger the driver code) could potentially crash the system (_kernel panic_), or in worst-case scenarios, execute code with kernel privileges.

Here’s a simplified version of how the problematic code path looks in nfcmrvl/main.c

// Vulnerable function (simplified)
void nfcmrvl_nci_unregister_dev(struct nci_dev *ndev)
{
    struct nfcmrvl_private *priv = nci_get_drvdata(ndev);

    // ... some cleanup steps ...

    kfree(priv); // Frees the device-specific data
}

// Elsewhere, async firmware download
void firmware_download_work(struct work_struct *work)
{
    struct nfcmrvl_private *priv = // ... get our struct ...

    // Use priv for firmware-related operations
    download_firmware(priv);

    // ... do stuff ...
}

What’s the Problem?

- If the cleanup (nfcmrvl_nci_unregister_dev) begins while the async firmware_download_work is running or about to run, priv might get freed (kfree(priv)) while it’s still in use.

The firmware work routine does *not* check if priv is still valid.

- If firmware_download_work uses priv after it’s freed, that is use-after-free. Attackers can exploit this scenario to manipulate kernel behavior.

Attackers would need to

1. Trigger firmware download (for example, by plugging in and initializing an NFC Marvell chip or device, or using custom tools).
2. Race the removal: Almost at the same time, they’d trigger cleanup/removal of the NFC device (nfcmrvl_nci_unregister_dev), possibly by removing, disabling, or rapidly reloading the driver.

Cause system crashes (denial-of-service).

- Under some conditions, control what’s in the freed memory, leading to code execution in kernel space.

Proof of Concept Snippet

Below is a pseudo-exploit code snippet to show the theory (this wouldn’t work directly without extra setup):

// Pseudocode: trigger race between firmware download and cleanup
int main() {
    // Step 1: Initialize and register the NFC device
    register_nfcmrvl_device(); // triggers firmware download async work

    // Step 2: Immediately trigger device removal and cleanup
    unregister_nfcmrvl_device(); // attempts to free the device memory

    // At this point, if unlucky, firmware download is still running, using freed memory
}

Note: Actual exploitation is much more complex due to timing, but security researchers have demonstrated races win in similar scenarios.

Reported: April 2022

- Fixed: Kernel maintainers patched the bug by adding proper synchronization (usually via mutexes or canceling async work before freeing memory).
- Fixed in: Linux Kernel Patch

Patch commit

// Cancel async work before freeing
cancel_work_sync(&priv->download_fw_work);
kfree(priv);

Technical References

- CVE Details for CVE-2022-1734
- Linux Kernel Git Patch
- Red Hat Vulnerability Portal
- NIST National Vulnerability Database

Conclusion

CVE-2022-1734 highlights the dangers of not synchronizing complex driver routines in OS kernels, especially when asynchronous work (like firmware downloads) can outlive the driver object. Even “small” kernel bugs are critical, because a use-after-free often leads to privilege escalation or at least denial of service.

Mitigation:

Upgrade your Linux kernel to a patched version.

- Always ensure hardware vendor device drivers are kept up to date, especially if you use NFC hardware.

Timeline

Published on: 05/18/2022 17:15:00 UTC
Last modified on: 07/07/2022 15:15:00 UTC