The Linux kernel is an essential part of the operating system, responsible for managing system resources and providing an interface between hardware and software components. Recently, a vulnerability has been identified and resolved in the Linux kernel’s netfilter “nf_tables” module. This blog post will delve into the details of this vulnerability (designated as CVE-2024-26925), share a code snippet demonstrating the issue, and provide links to the original references. Lastly, we'll discuss the potential exploit and its implications on system security.

Details of Vulnerability

The vulnerability in question is related to the improper handling of a mutex within the nf_tables module. Mutexes (short for "mutual exclusions") are used to prevent multiple instances of a program or function from accessing shared resources simultaneously. In this case, the mutex is associated with the nf_tables module and is used to perform garbage collection on expired netfilter objects.

This vulnerability resides in the critical section between “nft_gc_seq_begin()” and “nft_gc_seq_end()”. The “commit mutex” should not be released during this critical section, otherwise, the asynchronous garbage collection (GC) worker could collect expired objects and get the released commit lock within the same GC sequence.

The function “nf_tables_module_autoload()” temporarily releases the mutex to load module dependencies, but this should be moved to the end of the abort phase, after “nft_gc_seq_end()” is called.

Here's a code snippet that demonstrates the issue

static void nft_gc_seq_end(struct nft_ctx *ctx, struct nft_trans_ctx *trans)
{
    mutex_unlock(ctx->commit_mutex);
    ...
}

To resolve the issue, the mutex should be moved to the end of the abort phase

static void nft_gc_seq_end(struct nft_ctx *ctx, struct nft_trans_ctx *trans)
{
    ...
    mutex_unlock(ctx->commit_mutex);
}

- Linux Kernel Git Commit: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=139fdd1b065b6ae39a060f99a87873c6b8390678
- CVE Details: https://nvd.nist.gov/vuln/detail/CVE-2024-26925

Exploit Details

An attacker with local access to a vulnerable system could potentially exploit this issue by triggering a race condition, potentially leading to unexpected behavior, or in some cases, potentially even elevating their privileges on the system. It is crucial to patch the system with the latest Linux kernel updates to mitigate the risk of this vulnerability being exploited.

Conclusion

The recently resolved Linux kernel vulnerability CVE-2024-26925 demonstrates the complexity of a modern operating system and the potential risks associated with improper handling of mutexes. By understanding the issue and applying the appropriate patch, system administrators can help ensure the security and stability of their Linux systems.

Timeline

Published on: 04/25/2024 06:15:57 UTC
Last modified on: 12/19/2024 08:50:15 UTC