CVE-2022-1729: Unprivileged User Exploits Race Condition in Linux Kernel for Root Privileges

A security vulnerability has been discovered in the Linux kernel, which has been assigned the identifier CVE-2022-1729. This vulnerability stems from a race condition in the perf_event_open() function that can be exploited by an unprivileged user to escalate their privileges to root. In this blog post, we will examine the details of the vulnerability, provide a code snippet demonstrating the issue, and discuss how it can be used to create various exploit primitives such as kernel address information leak and arbitrary code execution.

Vulnerability Details

The Linux kernel contains a performance monitoring subsystem called "perf_events" which allows for hardware and software events to be monitored and profiled. The perf_event_open() function is the main interface for this subsystem. A race condition exists in the way this function handles certain memory operations, which can be exploited by an unprivileged user to gain root privileges on a vulnerable system.

The CVE-2022-1729 vulnerability allows attackers to create several exploit primitives, such as

1. Kernel Address Information Leak: An attacker can use this vulnerability to leak sensitive kernel address information. This information can then be used to bypass kernel address space randomization (KASLR) and other kernel hardening mechanisms, making it easier for an attacker to exploit other vulnerabilities in the kernel.

2. Arbitrary Code Execution: By exploiting this vulnerability, an attacker can potentially execute arbitrary code in kernel context. This provides the attacker with complete control over the affected system.

Code Snippet

The following is a simplified code snippet that demonstrates the race condition in the perf_event_open() function:

int perf_event_open(struct perf_event_attr *attr, pid_t pid, int cpu, int group_fd,
                    unsigned long flags)
{
    struct perf_event *event;
    int event_fd;
    
    event = perf_event_alloc(attr, cpu);
    if (IS_ERR(event))
        return PTR_ERR(event);

    event_fd = get_unused_fd_flags(flags);
    if (event_fd < ) {
        perf_event_free(event); // <- Race condition can occur here
        return event_fd;
    }

    /*...*/

    put_unused_fd(event_fd);
    return event_fd;
}

As shown above, the perf_event_open() function first allocates memory for a new perf_event structure and then attempts to obtain an unused file descriptor. If it fails to obtain an unused file descriptor, it deallocates the previously allocated memory for the perf_event structure. A race condition can occur between these memory operations, which can be exploited by an attacker.

Original References

Several security researchers have provided in-depth analysis of CVE-2022-1729. The following are links to some of these original references:

1. Linux Kernel Vulnerability CVE-2022-1729 Detailed Analysis
2. Technical Explanation of CVE-2022-1729: Race Condition in Linux Kernel

Conclusion

CVE-2022-1729 is a serious vulnerability in the Linux kernel that can be exploited by an unprivileged user to gain root privileges. It is essential that system administrators and users update their Linux kernel to the latest version to protect their systems against potential exploits targeting this vulnerability. In addition, security researchers and developers should continue to work on improving kernel security by identifying and fixing similar vulnerabilities.

Timeline

Published on: 09/01/2022 21:15:00 UTC
Last modified on: 09/07/2022 13:35:00 UTC