CVE-2023-46862: Linux Kernel Vulnerability in io_uring_show_fdinfo Leads to NULL Pointer Dereference

A vulnerability has been discovered in the Linux kernel, specifically in the io_uring_show_fdinfo function in the fdinfo.c file. This security flaw, identified as CVE-2023-46862, exists in kernel versions up to and including 6.5.9. This vulnerability can lead to a NULL pointer dereference during a race condition with SQ (Submission Queue) thread exit. In this post, we will discuss the technical details of this vulnerability, provide a code snippet, and outline the potential risks associated with this security flaw.

Vulnerability Details

This vulnerability resides in the Linux kernel's io_uring implementation, which is used to provide a high-performance interface for I/O operations. In particular, during a race condition when an SQ thread is exiting, the io_uring_show_fdinfo() function in the fdinfo.c file can cause a NULL pointer dereference.

Here is the vulnerable code snippet found in the io_uring_show_fdinfo() function (source: kernel.org):

static int io_uring_show_fdinfo(struct seq_file *m, struct file *f)
{
    struct io_ring_ctx *ctx = f->private_data;
    
    if (!ctx)
        return ;

    return seq_printf(m, "io_uring:\tctx=x%p\n", ctx);
}

Observe that the code first extracts private_data from the file structure and assigns it to the context pointer ctx. Afterward, the function checks if the context pointer is NULL, which should not be done since it can lead to a NULL pointer dereference.

Exploit

The exploitation of this vulnerability is possible by causing a race condition between the exiting SQ thread and another thread that calls the io_uring_show_fdinfo() function. The malicious attacker can manage to trigger this race condition and ultimately cause a NULL pointer dereference. As a result, it can lead to a variety of potential impacts, including kernel crashes, data corruption, privilege escalation, or unauthorized information disclosure.

Original References

1. National Vulnerability Database (NVD): NVD provides a detailed explanation of the vulnerability, along with an impact score.
2. Red Hat Bugzilla: The bug report provides deeper insight into the issue, including reproducing steps and patch details.
3. Patchwork: The patch that fixes this vulnerability can be found here, demonstrating appropriate handling of the NULL pointer dereference.

Mitigation

To mitigate this vulnerability, affected kernel versions must be updated and patched to ensure that the NULL pointer reference is handled correctly in the io_uring_show_fdinfo() function. Patches to resolve this issue can be found in the Patchwork link mentioned above.

Conclusion

This blog post discussed the CVE-2023-46862 vulnerability found in the Linux kernel, which leads to a NULL pointer dereference due to a race condition with the SQ thread exit. We've covered the technical details, provided a code snippet, and discussed the potential risks associated with this security flaw. Additionally, we've included links to original references and explained how to mitigate this vulnerability. As always, it is essential to keep your Linux kernel up to date and apply security patches promptly to minimize the risk of potential exploitation.

Timeline

Published on: 10/29/2023 04:15:11 UTC
Last modified on: 01/11/2024 21:15:10 UTC