The Linux kernel powers billions of devices, but sometimes even a small oversight in handling data types can cause real trouble. One such issue is CVE-2024-57899 — a vulnerability that affected Wi-Fi management in the Linux kernel’s mac80211 subsystem, specifically in mesh networking on 32-bit systems. If you run Linux on older or embedded gear, read on to see how this could have let bugs slip through, why it’s now fixed, and what you need to know as a sysadmin, developer, or security enthusiast.

What is CVE-2024-57899?

- Vulnerability: Incorrect bit-flag checking due to mixing unsigned long (4 bytes on 32-bit systems) and u64 (8 bytes).

Subsystem: Wi-Fi (mac80211), particularly for Mesh Basic Service Sets (MBSS).

- Impact: Corrupted calculation of which flags have changed — could lead to logic errors, unstable mesh network behavior, or potential denial of service if exploited.

Linux kernel on 32-bit architectures (like ARM, x86, MIPS in 32-bit mode, etc).

- Devices using Wi-Fi mesh networking (routers, IoT devices, some mobile/embedded Linux distros).

The Problem – Why Data Types Matter

Let’s look at the root cause. Suppose you want to check which flags changed in some Wi-Fi mesh code. You store the flags in a variable:

unsigned long changed; // 4 bytes (32 bits) on 32-bit systems

But the code assumes it can scan 64 bits of changes, using

or_each_set_bit(bit, &bits, sizeof(changed) * BITS_PER_BYTE)

However, on 32-bit, sizeof(changed) is 4, not 8! The result: the code never checks the higher 32 bits, or may even start reading memory beyond the variable boundary (if programmed incorrectly).

Before the fix (simplified)

unsigned long changed; // 32 bits on 32-bit system
// ...
or_each_set_bit(bit, &changed, 64); // Incorrect! Only 32 bits in 'changed'

After the fix

unsigned long changed;
// Properly use the variable's real size
or_each_set_bit(bit, &changed, sizeof(changed) * 8); // Now 32 on 32-bit, 64 on 64-bit

Could an attacker do anything bad?

While this bug alone doesn’t give direct privilege escalation or code execution, it creates confusion in the kernel’s flag state:

Mesh syncing, state updates, and notifications may misfire.

- A skilled attacker on the network could try to craft packets to manipulate mesh state, potentially causing mesh instability or a denial of service.

In embedded/IoT scenarios, such bugs can cascade into weird instability.

If you’re a developer or sysadmin, you might have seen something like this in dmesg

Call Trace:
 ? show_regs+x54/x58
 ? __warn+x6b/xd4
 ? ieee80211_link_info_change_notify+xcc/xd4 [mac80211]
 ...
 ? ieee80211_mesh_work+xff/x260 [mac80211]
 ? cfg80211_wiphy_work+x72/x98 [cfg80211]
 ...

These logs show where the kernel code tripped up — often in the mesh work or link notification jobs.

Official Fix

The Linux kernel developers fixed this by adjusting the code to always match the size of the variable for the current architecture. No more bit math errors!

Patch summary

> Solution: Ensure that the size of the bits variable is correctly adjusted for each architecture.

- Kernel.org Commit: wifi: mac80211: fix mbss changed flags corruption on 32 bit systems
- NVD Entry for CVE-2024-57899 *(may take a few days to appear)*
- mac80211 subsystem docs
- Linux Wi-Fi Mesh Networking

Update your kernel

Make sure you are running a kernel version with the patch for CVE-2024-57899, especially on 32-bit embedded, routers, or IoT hardware.

Check for kernel logs

If you use mesh, scan dmesg/syslog for “ieee80211_link_info_change_notify” or similar messages.

Summary

- Mixed 32-bit / 64-bit code can open weird bugs that might risk stability or security.

Timeline

Published on: 01/15/2025 13:15:14 UTC
Last modified on: 05/04/2025 10:06:11 UTC