CVE-2026-31475 Overview
A double free vulnerability has been identified in the Linux kernel's ASoC (ALSA System on Chip) subsystem, specifically in the sma1307 audio amplifier driver. The vulnerability occurs in the sma1307_setting_loaded() function where device-managed memory allocated with devm_kzalloc() is incorrectly freed using kfree(), leading to a double free condition when the device resource management (devres) system later attempts to release the same memory.
Critical Impact
This double free vulnerability in the Linux kernel can lead to memory corruption, kernel instability, or potentially be leveraged for privilege escalation in local attack scenarios.
Affected Products
- Linux kernel with ASoC sma1307 driver enabled
- Systems using Iron Device SMA1307 audio amplifier components
- Embedded Linux devices with affected kernel versions
Discovery Timeline
- 2026-04-22 - CVE CVE-2026-31475 published to NVD
- 2026-04-23 - Last updated in NVD database
Technical Details for CVE-2026-31475
Vulnerability Analysis
The vulnerability stems from incorrect memory management in the sma1307_setting_loaded() function within the Linux kernel's ASoC subsystem. A previous commit introduced NULL checks and cleanup logic for allocation failures, but the implementation incorrectly used manual kfree() calls to free mode_set entries that were allocated using devm_kzalloc().
The devm_kzalloc() function is part of the Linux kernel's device resource management framework, which automatically tracks and frees allocations when the device is detached or the driver is unloaded. By manually calling kfree() in the error path, the code creates a situation where the same memory region is freed twice—once manually and once by the devres cleanup routine.
This double free condition can corrupt kernel memory management structures, potentially leading to system instability, kernel panics, or in certain exploitation scenarios, arbitrary code execution within kernel context.
Root Cause
The root cause is a misunderstanding of the device-managed memory allocation semantics in the Linux kernel. Memory allocated with devm_kzalloc() is automatically managed by the devres framework and should not be manually freed with kfree(). The erroneous cleanup code introduced a manual kfree() loop for mode_set entries in the error handling path, conflicting with the automatic resource management that was already in place.
Attack Vector
This vulnerability requires local access to the system with the ability to trigger driver initialization or error conditions in the sma1307 audio driver. An attacker would need to cause allocation failures during the sma1307_setting_loaded() function execution to trigger the vulnerable error path. While exploitation complexity is elevated due to the need for precise timing and kernel memory layout manipulation, successful exploitation could lead to privilege escalation or denial of service.
The attack surface is primarily limited to systems that:
- Have the SMA1307 audio amplifier hardware or driver loaded
- Allow unprivileged users to interact with audio subsystems
- Run vulnerable kernel versions
Detection Methods for CVE-2026-31475
Indicators of Compromise
- Kernel panic or oops messages referencing sma1307 driver functions
- Memory corruption warnings in kernel logs related to SLUB/SLAB allocator
- System instability when loading or unloading ASoC audio drivers
- Unexpected kernel memory allocation failures in audio subsystem
Detection Strategies
- Monitor kernel logs (dmesg) for double free warnings or memory corruption messages
- Use kernel debugging tools like KASAN (Kernel Address Sanitizer) to detect memory safety violations
- Implement system monitoring for unexpected kernel panics or driver crashes
- Review loaded kernel modules for presence of vulnerable snd_soc_sma1307 driver
Monitoring Recommendations
- Enable kernel memory debugging options (CONFIG_DEBUG_KMEMLEAK, CONFIG_KASAN) in development environments
- Configure automated log analysis to alert on ASoC or memory management anomalies
- Monitor system stability metrics for audio driver-related issues
- Implement kernel module integrity checking to ensure patched versions are deployed
How to Mitigate CVE-2026-31475
Immediate Actions Required
- Update the Linux kernel to a patched version containing the fix
- If immediate patching is not possible, consider unloading the snd_soc_sma1307 driver module if not required
- Review systems for signs of exploitation or memory corruption
- Prioritize patching on systems where untrusted users have local access
Patch Information
The fix removes the erroneous manual kfree() loop and allows the devres framework to handle cleanup of devm_kzalloc() allocated memory as intended. The following kernel patches address this vulnerability:
Apply the appropriate patch for your kernel version from the stable kernel repository.
Workarounds
- Unload the snd_soc_sma1307 kernel module if audio amplifier functionality is not required: modprobe -r snd_soc_sma1307
- Blacklist the driver module to prevent automatic loading by adding blacklist snd_soc_sma1307 to /etc/modprobe.d/blacklist.conf
- Restrict access to audio device nodes to limit exposure to untrusted local users
- Deploy kernel live patching solutions if available for your distribution
# Workaround: Blacklist the vulnerable driver module
echo "blacklist snd_soc_sma1307" | sudo tee /etc/modprobe.d/blacklist-sma1307.conf
sudo update-initramfs -u
# Unload the module if currently loaded
sudo modprobe -r snd_soc_sma1307
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
