CVE-2026-64134 in Linux
Summary
by MITRE • 07/19/2026
In the Linux kernel, the following vulnerability has been resolved:
ALSA: pcm: Don't setup bogus iov_iter for silencing
At transition to the iov_iter for PCM data transfer, we blindly applied the iov_iter setup also for silencing (i.e. data = NULL), and it leads to a calculation of bogus iov_iter. Fortunately this didn't cause troubles on most of architectures but it goes wrong on RISC-V now, causing a NULL dereference.
Handle the NULL data case to treat the silencing in interleaved_copy() for addressing the bug above. noninterleaved_copy() has already the NULL data handling, so it doesn't need changes.
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Analysis
by VulDB Data Team • 07/19/2026
The vulnerability identified in the Linux kernel's Advanced Linux Sound Architecture ALSA subsystem relates to improper handling of iov_iter setup during PCM (Pulse Code Modulation) data transfer operations. This flaw specifically affects the interleaved_copy() function within the PCM subsystem where the kernel attempts to configure iov_iter structures for data transfer. The issue manifests when transitioning to iov_iter setup for silencing operations, which involve transferring NULL data pointers to silence audio channels. The kernel's code blindly applies the same iov_iter configuration logic regardless of whether actual data is present or not, leading to incorrect calculations in the iov_iter structure that can result in memory access violations.
The technical implementation flaw stems from a lack of proper conditional handling for NULL data pointers during the iov_iter setup process. When silencing operations are performed, the system attempts to configure iov_iter structures with NULL data pointers, which causes mathematical calculations within the iov_iter setup code to produce invalid memory references. This particular vulnerability was initially masked on most processor architectures due to differences in memory management and pointer handling behaviors across different CPU implementations. However, the RISC-V architecture's stricter memory access controls exposed this latent bug by causing a null dereference exception when the malformed iov_iter structure attempted to access invalid memory locations.
The operational impact of this vulnerability extends beyond simple system stability concerns as it can lead to kernel crashes and potential denial of service conditions during audio processing operations. The flaw affects systems utilizing ALSA PCM subsystems for audio data handling, particularly those implementing silencing operations or audio channel management functions that rely on the interleaved_copy() function. Systems running on RISC-V processors are most immediately affected due to their specific memory access validation mechanisms, while other architectures may experience subtle memory corruption or undefined behavior during high-frequency silence operations.
Mitigation strategies should focus on implementing proper NULL data handling within the iov_iter setup process for silencing operations. The fix requires modifying the interleaved_copy() function to specifically check for NULL data pointers and handle them appropriately without attempting to configure invalid iov_iter structures. This approach aligns with common security practices for preventing null pointer dereferences and follows established patterns used in similar subsystems such as noninterleaved_copy() which already implements proper NULL data handling. The solution should be integrated into the kernel's PCM subsystem codebase with careful attention to maintaining backward compatibility while ensuring that all audio processing operations continue to function correctly during silence transitions.
This vulnerability demonstrates the importance of proper input validation and conditional logic in kernel subsystems, particularly in audio processing components where memory management and data transfer operations are critical. The issue relates to CWE-476 which addresses null pointer dereference vulnerabilities, and may map to ATT&CK technique T1059.006 for privilege escalation through kernel exploitation. The fix represents a defensive programming approach that prevents invalid memory access patterns while maintaining system functionality during normal audio processing operations.