In this post, we will dive deep into an important vulnerability that has been resolved in the Linux kernel: CVE-2024-56584. It involves the io_uring subsystem and its associated potential for memory allocation errors. We will discuss the details of the issue, walk you through a code snippet that demonstrates the problem, and provide a workaround to fix the vulnerability.

Main Content

The discovered vulnerability CVE-2024-56584 resides in the Linux kernel, particularly within the area responsible for the io_uring subsystem (io_uring/tctx). In certain scenarios, a memory allocation error may occur, leading to unexpected warnings and potential system instability.

The issue was initially brought to attention by syzbot, which produced the following WARN_ON

WARNING: CPU:  PID: 16 at io_uring/tctx.c:51 __io_uring_free+xfa/x140 io_uring/tctx.c:51

This is caused by the following sanity check in the __io_uring_free() function, executed when an io_uring_task is undergoing its final put():

WARN_ON_ONCE(!xa_empty(&tctx->xa));

To understand the root cause, it is crucial to note that the syzbot test case involved memory allocation failures. As a result, we can infer that xa_store() may encounter a memory allocation error, leaving ->head as non-NULL even though there are no entries in the xarray.

Workaround

To circumvent the issue, we must iterate through the entries in tctx->xa from the io_uring subsystem and invoke a WARN_ON_ONCE() if an entry is found. Here is a code snippet demonstrating this approach:

unsigned long index;
void *entry;
xa_for_each(&tctx->xa, index, entry) {
    WARN_ON_ONCE(1);
}

This workaround helps us ensure that memory allocation errors are properly handled and do not lead to system instability or other undesired consequences.

References

For more information and context on this vulnerability and its resolution, please refer to the following resources:

- Linux Kernel Mailing List (LKML) - io_uring/tctx Workaround
- io_uring Subsystem GitHub Repository
- Syzbot Test Case and Report

Conclusion

CVE-2024-56584 is a serious vulnerability in the Linux kernel that affects the io_uring subsystem. Thanks to syzbot's diligent testing, this issue has been identified and a workaround has been developed. By ensuring that memory allocation errors are correctly managed, we can continue to maintain the stability and performance of our Linux systems.

If you have any questions or concerns about this vulnerability or its resolution, please do not hesitate to reach out or consult the resources provided above for more information. Remember that keeping our systems updated and well-maintained is key to their security and longevity.

Timeline

Published on: 12/27/2024 15:15:17 UTC
Last modified on: 03/06/2025 15:37:47 UTC