Summary:
CVE-2024-53190 is a recently patched vulnerability in the Linux kernel's rtlwifi driver, impacting systems using Realtek USB WiFi adapters. The issue arises from an excessive retry loop that could cause driver hangs and serious system slowdowns. Below we’ll break down what happened, why it matters, see some code snippets, outline a real-world exploit scenario, and provide resources to learn more.

What Happened?

When plugging in certain Realtek USB WiFi adapters (tested with emulation by fuzzers like Syzkaller), Linux runs the rtlwifi driver. In this driver, the initialization process includes reading from the device’s EEPROM (“efuse”). If this operation fails, a function called read_efuse_byte() repeatedly retries—up to 10,000 times before giving up.

When the driver is used with USB devices, hardware or emulation faults can cause these retries to all fail (like when using Syzkaller’s dummy_hcd for fuzzing). Each retry is slow, and the endless loop can hang the driver probe for 15 seconds or more per byte, sometimes grinding the host system to a halt or causing stuck kworker tasks (critical kernel threads).

This is a Denial of Service (DoS) risk and an annoyance for normal users, but can be reliably triggered by attackers or testing tools.

Technical Details & Code

The vulnerable retry loop lives in the drivers/net/wireless/realtek/rtlwifi/rtl_usb.c and related Realtek driver code like hal/rtl8192cu/efuse.c.

Old Vulnerable Code (simplified)

#define EFUSE_READ_RETRY 10000  // excessive retries

int read_efuse_byte(struct ieee80211_hw *hw, u16 addr, u8 *data)
{
    int i;
    for (i = ; i < EFUSE_READ_RETRY; i++) {
        res = usb_control_msg(...);
        if (res == ) {
            *data = ...;
            return ;    // Success
        }
        msleep(1);  // Slowdown per retry
    }
    return -EIO;    // All retries failed
}

Patched Code (fixed v6.12 and up)

#ifdef CONFIG_USB
#define EFUSE_READ_RETRY 10      // drastically reduced for USB devices
#else
#define EFUSE_READ_RETRY 10000   // keep high for PCI, if needed
#endif

// Rest of function unchanged, but now capped for USB

Stacktrace Example

When triggered, a hung kworker process appears, stalling the USB subsystem (see full syzkaller report):

task:kworker/:3 state:D stack: pid:662 tgid:662 ppid:2 flags:x00004000
Workqueue: usb_hub_wq hub_event
Call Trace:
 __schedule+xe22/xeb6
 schedule_timeout+xe7/x132
 __wait_for_common+xb5/x12e
 usb_start_wait_urb+xc5/x1ef
 ...
 read_efuse_byte+x13c/x146
 read_efuse+x351/x5f
 ...

---

Real-World Exploit Scenario

Suppose an attacker can emulate or fuzz USB devices on your Linux machine (as is common in guest/host research or in environments where users can attach USB gadgets). They could:

Craft a USB device that persistently fails efuse read.

2. Plug it in, or trigger via virtualization/hardware simulators.

The kernel’s kworker thread (handling USB events) gets stuck retrying 10,000 times per byte read.

4. System becomes unresponsive for tens of seconds, especially if multiple such devices are connected or probed in parallel.

In targeted attacks, this could be part of a resource exhaustion/denial of service toolkit, or in the lab, a way to defeat WiFi device probing/fuzz further kernel code.

Reproducing with Syzkaller

If you want to see this in action (be careful!), you can use the Syzkaller fuzzer with raw-gadget/dummy_hcd to emulate a failing USB device:

C reproducer:

syzkaller repro code

3. Run the repro code.

4. Watch the system hang with "kworker/usb_hub_wq" stuck in D-state, as above.

Mitigation and Solution

- Patched kernels (mainline 6.12+, and potentially backported) cap USB efuse read retries at just 10, instantly making the bug harmless on modern systems.

References

- Commit fixing the bug (git.kernel.org)
- syzkaller issue report/thread
- C Reproducer by Syzkaller

TL;DR

CVE-2024-53190 is a high-impact kernel bug in rtlwifi’s efuse read routine. It allowed excessive I/O retries on device errors, freezing the host system for long periods. The bug is trivial to exploit (simply plug in a broken emulated USB device), but is fully fixed in Linux kernel 6.12 and later by capping the retry count.

If you use Realtek USB WiFi on Linux — update your kernel now!

*This explanation is exclusive and focused for general users and sysadmins. Reach out to the kernel links for the latest upstream details and patching guides.*

Timeline

Published on: 12/27/2024 14:15:26 UTC
Last modified on: 05/04/2025 09:55:21 UTC