The Linux kernel, at the core of the Linux operating system, plays a crucial role in ensuring the stability, security, and performance of millions of applications and servers worldwide. As such, any vulnerability in the kernel can have far-reaching consequences. In this long-read post, we will discuss a recently resolved vulnerability in the Linux kernel, its significance, and potential exploits. We will also provide code snippets and references to the original patch to better understand the solution.

Vulnerability Details

In the Linux kernel, a vulnerability was discovered in the net/smc (kernel's Socket Memory Communication) implementation. Specifically, this vulnerability relates to the handling of proposal messages received by an SMC server. The fields 'iparea_offset' and 'ipv6_prefixes_cnt' in these proposal messages come from a remote client and cannot be fully trusted. In certain scenarios, if the 'iparea_offset' field exceeds the maximum allowed value, the resulting access to an incorrect address leads to a crash, potentially compromising the stability and security of the affected server.

Code Snippet

To resolve this issue, the latest patch introduces validation checks for the 'iparea_offset' and 'ipv6_prefixes_cnt' fields before utilizing them. Here is a code snippet from the patch that highlights the added validation:

/* smc_core.c: SMC Protocol Processing Routines */
// ...

static int smc_listen_work(struct smc_sock *smc)
{
struct smc_init_info conn_info;
int rc = SMC_CLC_DECL_REPLY_NEG;
smc->listen_cookie = smc_listen_work_pending;

// ... (other code)

/* check the received ipv6_prefixes_cnt and iparea_offset values */
if (unlikely(conn_info.prompt.ipv6_prefixes_cnt > SMC_MAX_IPV6_PREFIXES
   || (conn_info.iparea_offset > SMC_CLC_DECL_OFFSET_MAX))) {
   pr_warn_ratelimited("smc: Invalid ipv6_prefixes_cnt or iparea_offset\n");
   goto free_val_buf;
}

// ... (other code)

Exploit Details

In order to understand the potential implications of this vulnerability, let us consider a scenario where an attacker crafts a malicious proposal message with an 'iparea_offset' value exceeding the maximum allowed value. This message, when received by the SMC server, would cause it to access an incorrect address. As a result, the system may crash, leading to Denial of Service (DoS) attacks. An attacker may try to exploit this vulnerability to disrupt the operations of the targeted server.

Original References

The patch that resolves this vulnerability can be found in the Linux kernel source tree and is named "net/smc: check iparea_offset and ipv6_prefixes_cnt when receiving proposal msg." You can also view the details of this patch on the public Linux kernel mailing list archives: Link

Additionally, the CVE entry for this vulnerability, CVE-2024-49571, provides further information about its associated risks and potential impact: Link

Conclusion

In summary, the Linux kernel developers addressed a critical vulnerability in net/smc by adding validation checks for the 'iparea_offset' and 'ipv6_prefixes_cnt' fields when receiving proposal messages. By checking these values before use, the stability and security of the server are better safeguarded against potential attacks. To protect your Linux-based systems, ensure that you apply the latest patches and updates, keeping your kernel up to date and secure.

Timeline

Published on: 01/11/2025 13:15:24 UTC
Last modified on: 01/20/2025 06:19:19 UTC