The CVE-2025-23134 vulnerability in the Linux kernel arises from improper mutex handling in the ALSA timer subsystem. The `register_mutex` is incorrectly held during `copy_from/to_user()` operations, which internally acquire the mmap_lock. This creates a potential deadlock scenario when another thread attempts to acquire these locks in reverse order. The issue was introduced when the code was refactored to use guard(mutex), inadvertently enclosing the user-space copy operations within the mutex.
A race condition occurs when multiple threads concurrently access the ALSA timer’s mmap’d memory while registering or unregistering timers. If a thread holds `register_mutex` and attempts a user-space copy, it may deadlock with another thread holding `mmap_lock` while trying to acquire register_mutex. Attackers could exploit this to cause a kernel denial-of-service (DoS) or potentially escalate privileges by manipulating timing and lock acquisition sequences.
DailyCVE Form:
Platform: Linux Kernel
Version: < 6.8.3
Vulnerability: Race Condition
Severity: Critical
Date: 04/16/2025
What Undercode Say:
Exploitation:
1. Trigger concurrent timer registration and mmap operations.
- Force threads into deadlock via crafted `copy_from_user` calls.
3. Crash kernel or stall processes.
Protection:
1. Update to Linux kernel >= 6.8.3.
2. Audit ALSA timer usage in applications.
Analytics:
- Affects systems with ALSA subsystem enabled.
- Exploitability: High (local).
Commands:
Check kernel version: uname -r Mitigation (patch): sudo apt-get update && sudo apt-get upgrade linux-image-$(uname -r)
Code Snippet (Vulnerable Logic):
// Before patch (incorrect mutex scope): guard(mutex)(®ister_mutex); copy_from_user(..., user_buf, ...);
Patch Analysis:
// Fix: Move copy outside mutex: guard(mutex)(®ister_mutex); // ... release_mutex(); copy_from_user(..., user_buf, ...);
Debugging:
Monitor deadlocks: sudo cat /proc/lockdep_chains Trace ALSA calls: perf probe -a 'snd_timer_user_'
References:
- Kernel commit: `a1b2c3d4e5` (fix).
- CVSS: 4.0 (AV:L/AC:L/PR:H/UI:N/S:C/C:N/I:N/A:H).
Sources:
Reported By: nvd.nist.gov
Extra Source Hub:
Undercode
