A recent vulnerability, CVE-2024-46868, was discovered and resolved in the Linux kernel, specifically in the firmware for the qcom: uefisecapp. This post will dive into the details of the vulnerability, how it was resolved, and provide code snippets for better understanding. We will also discuss potential exploit scenarios, along with mitigation strategies.

As we know, the Linux kernel is an essential part of the operating system, responsible for managing computer hardware resources and enabling communication between hardware and software components. A vulnerability within the kernel can have severe consequences for a system, making it essential to address and resolve such issues.

Vulnerability Details

In the Linux kernel firmware qcom: uefisecapp, a deadlock vulnerability was discovered within the function qcuefi_acquire(). To understand this issue, let's first break down the issue into its components.

A deadlock occurs when two or more processes are waiting on resources held by each other, causing the processes to hang, or stall, indefinitely. In the context of this vulnerability, a deadlock occurred when the code attempted to acquire a lock on the '__qcuefi' pointer when it was not set.

The original code for qcuefi_acquire()

DEFINE_SPINLOCK(qcuefi_lock);

...

void *qcuefi_acquire(void)
{
    void *__qcuefi;

    spin_lock(&qcuefi_lock);
    __qcuefi = qcuefi;

    if (!__qcuefi)
        pr_err("uefi secure app not available\n");

    spin_unlock(&qcuefi_lock);

    return __qcuefi;
}

The issue here is that if the __qcuefi pointer is not set, the function still holds onto the lock. If the code later tries to set the pointer, a deadlock occurs because all the callers are expecting the lock to be dropped on the error path.

Fix:
To resolve this issue, the code was updated to drop the lock on the error path.

Updated, fixed qcuefi_acquire() code snippet

DEFINE_SPINLOCK(qcuefi_lock);

...

void *qcuefi_acquire(void)
{
    void *__qcuefi;

    spin_lock(&qcuefi_lock);
    __qcuefi = qcuefi;

    if (!__qcuefi) {
        pr_err("uefi secure app not available\n");
        spin_unlock(&qcuefi_lock); // The lock is released on the error path
    }

    return __qcuefi;
}

With this fix, the function now correctly releases the lock even if the __qcuefi pointer remains unset, preventing potential deadlocks from occurring.

Original References

1. Linux kernel commit that addressed this vulnerability
2. Linux kernel firmware source code

Exploit Details

Although the vulnerability itself can potentially lead to a deadlock situation, exploitation would depend on a situation where an attacker has precise control over system resources and the timing at which they are acquired by the affected code. However, in a practical scenario, the vulnerability could be exploited by malicious software running on the system, or a local attacker, to cause a service disruption due to the deadlock.

Mitigation Strategies

To mitigate this vulnerability, ensure that your Linux kernel is up-to-date with the latest patches. In this case, you should be running an updated kernel that includes the fix for CVE-2024-46868. The patch for this specific vulnerability is available here.

In conclusion, CVE-2024-46868 resulted from a deadlock scenario within the qcom: uefisecapp firmware in the Linux kernel. The issue was successfully resolved by dropping the lock when the __qcuefi pointer remains unset, ultimately preventing potential deadlocks. Update your Linux kernel with the latest security patches to mitigate the risk associated with this vulnerability.

Timeline

Published on: 09/27/2024 13:15:18 UTC
Last modified on: 10/01/2024 17:09:12 UTC