CVE-2024-56707 - Critical Linux Kernel Patch for octeontx2-pf mbox Message Handling

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Overview

A serious flaw, CVE-2024-56707, was identified and fixed in the Linux kernel driver for Marvell's OcteonTX2 network interface card (NIC). Specifically, the octeontx2-pf driver was not properly handling error pointers after calling otx2_mbox_get_rsp() in otx2_dmac_flt.c. This left the driver vulnerable to kernel crashes and potentially other issues when mailbox messages failed.

What is CVE-2024-56707?

CVE-2024-56707 is a vulnerability in the communication between the Linux kernel and Marvell OcteonTX2 hardware through mailbox (mbox) messages. Mailbox messages are a way for kernel code and hardware firmware to communicate.

The problematic code failed to check if otx2_mbox_get_rsp() returned an error (an "error pointer"). Skipping this check could cause the kernel to access invalid memory or take faulty actions, leading to kernel panics, crashes, or other unforeseen behavior.

Vulnerable Area

The flaw was present in drivers/net/ethernet/marvell/octeontx2/af/otx2_dmac_flt.c — specifically, in functions that call otx2_mbox_get_rsp(), such as when a user/admin updates dynamic MAC filters via this driver:

static int otx2_dmac_flt_add(struct otx2_nic *pf, ...)
{
    ...  
    rsp = otx2_mbox_get_rsp(&pf->mbox, , &rsp_size);
    // No error check here – BAD!
    ...
}

What Went Wrong?

The code above immediately tries to use rsp. But if otx2_mbox_get_rsp() failed, rsp is actually a special error value – not real data. Accessing it can crash the kernel or cause unpredictable behavior.

How Was It Patched?

A fix was submitted and merged, which uses the standard IS_ERR() macro to check for error pointers, handling errors safely:

rsp = otx2_mbox_get_rsp(&pf->mbox, , &rsp_size);
if (IS_ERR(rsp))
    return PTR_ERR(rsp);   // Exit safely, reporting the error

With this patch, if the mailbox communication fails, the function will not try to use an invalid response. Instead, it propagates the error up and lets higher-level logic handle it.

Before

rsp = otx2_mbox_get_rsp(&pf->mbox, , &rsp_size);
// No check! Using rsp blindly may crash
process_rsp(rsp);

After

rsp = otx2_mbox_get_rsp(&pf->mbox, , &rsp_size);
if (IS_ERR(rsp))
    return PTR_ERR(rsp);  // Fail safely!
process_rsp(rsp);

Why Does This Matter?

If this driver is used (on Marvell OcteonTX2-based NICs), and if the mailbox mechanism fails (for example, due to bad hardware, firmware, memory shortages, or malicious input), the kernel can be crashed by simply triggering mailbox errors. This could be exploited for Denial of Service (DoS).

Exploit Scenario

While this bug doesn’t immediately enable privilege escalation, a local user or rogue process could intentionally trigger mailbox message errors by misconfiguring filters or flooding the mbox, causing kernel panic:

# Hypothetical (not an actual PoC)
ip link set dev eth up
while :; do
  ethtool -N eth flow-type ether src 00:00:00:00:00:00
done
# If mailslot is exhausted, otx2_mbox_get_rsp will fail,
# leading to crash or Oops without the patch.

A remote, authenticated attacker or a bug in admin scripts could also cause service disruption.

Mitigations & Recommendations

- Upgrade your kernel! Make sure to run a version with the fix backported—see your Linux distribution advisories or manually review the patch below.
- Restrict access: Do not let untrusted users run tools like ethtool or manipulate NIC filters before patching.

Patch Reference

- Kernel.org Commit Link (official patch)
- Marvell driver upstream discussion

References

- CVE Record at NIST
- Kernel Mailing List Patch Discussion
- OcteonTX2 Linux Driver README (hardware docs)

Summary

CVE-2024-56707 reminds us that error handling is critical in kernel/hardware interfaces. Especially when malicious or unexpected input is possible, robust checking can prevent catastrophic faults. If you manage servers with Marvell OcteonTX2 NICs, be sure to update your kernel to include the above patch.

Stay safe, and always keep an eye out for missing error checks in critical low-level code!

Timeline

Published on: 12/28/2024 10:15:19 UTC
Last modified on: 05/04/2025 10:02:57 UTC