CVE-2021-47081: Linux Kernel Vulnerability - habanalabs/gaudi: Fixing Potential Use-After-Free in gaudi_memset_device_memory

The Linux kernel is always under constant scrutiny and updates to fix vulnerabilities that arise from time to time. With the discovery of CVE-2021-47081, a potential use-after-free vulnerability in the habanalabs/gaudi subsystem, developers have been quick to respond with a patch to resolve it. In this article, we'll delve into the details of this vulnerability, discuss its implications, and see how the Linux kernel developers have addressed the issue. We'll also look at the code snippet that gave rise to this vulnerability and the measures taken to mitigate it.

Vulnerability Details

The CVE-2021-47081 vulnerability specifically affects the gaudi_memset_device_memory function within the habanalabs/gaudi subsystem. This vulnerability, if exploited, could potentially lead to unauthorized access, memory corruption, or even a complete crash of the system.

The root cause of this vulnerability is a use-after-free (UAF) issue, which was reported by a code analyzer.

To provide a better understanding, let's take a closer look at the code snippet where the vulnerability was discovered:

In gaudi_memset_device_memory, cb is get via hl_cb_kernel_create()
with 2 refcount.
If hl_cs_allocate_job() failed, the execution runs into release_cb
branch. One ref of cb is dropped by hl_cb_put(cb) and could be freed
if other thread also drops one ref. Then cb is used by cb->id later,
which is a potential uaf.

In this snippet, a control block cb is being created with a reference count of 2. However, if hl_cs_allocate_job() fails, then the execution flow moves to the release_cb branch, which decreases the reference count for cb by calling hl_cb_put(cb). If another thread drops a reference at the same time, cb can be freed, and then cb is used later with cb->id, creating the potential use-after-free vulnerability.

Patch

The developers have issued a patch that addresses the problem by introducing a variable named id to hold the value of cb->id before calling hl_cb_put(cb). This ensures that even if the memory block cb is freed, the id variable still contains a valid value, eliminating the potential use-after-free vulnerability.

Conclusion

The discovery and subsequent patching of the CVE-2021-47081 vulnerability in the Linux kernel highlight the importance of continuous monitoring, analysis, and improvements in the open-source community. By understanding and addressing potential issues like this one, the Linux kernel and its developers continue to ensure stability and security for countless applications and users worldwide.

For more information on the original references and code snippets, you can visit the following links

1. Habanalabs/gaudi source code on GitHub
2. CVE-2021-47081 - MITRE
3. Linux kernel mailing list discussion

Remember to always keep your software updated and watch for new patches to ensure your systems remain secure.

Timeline

Published on: 03/01/2024 22:15:47 UTC
Last modified on: 05/29/2024 05:01:47 UTC