CVE-2026-80716 in Linux
Summary
by MITRE • 08/28/2026
In the Linux kernel, the following vulnerability has been resolved:
ALSA: pcm: wake linked drain waiters on unlink
snd_pcm_drain() on a linked stream parks an on-stack wait entry on the drained peer's runtime->sleep, and after schedule_timeout() removes it only if that peer is still found in the caller's group. If group membership changes during the wait and the sleep ends by signal or timeout (so autoremove_wake_function() does not run), finish_wait() is skipped and snd_pcm_drain() returns with the entry still queued on that stream's sleep list; a later wake_up() then walks a freed stack frame. This is reachable by unlinking either the drained or the draining stream.
Unlike the close path (snd_pcm_drop() -> snd_pcm_post_stop()), snd_pcm_unlink() never wakes the sleep queues. Wake every group member under the group lock before the membership change, so a linked drainer is released and drops its entry while the streams are still grouped.
The window was opened when snd_pcm_link_rwsem stopped being held across the wait and the removal became conditional on group membership (see Fixes). The later switch to finish_wait() kept that conditional removal, so the signal/timeout case remained.
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Analysis
by VulDB Data Team • 08/28/2026
This vulnerability represents a critical use-after-free condition within the Advanced Linux Sound Architecture subsystem of the Linux kernel, specifically affecting the PCM audio stream management logic. The flaw resides in the implementation of snd_pcm_drain(), which is responsible for ensuring that all pending data on an audio stream is played out before the stream is considered closed or drained. When dealing with linked streams, where multiple PCM devices are synchronized to play simultaneously, the function parks a wait entry on the stack frame of the calling process onto the sleep queue of its peer stream. This mechanism allows the draining stream to block until the peer has finished processing its audio buffer. The core technical flaw arises from an improper handling of group membership changes during this waiting period. Specifically, if the relationship between the linked streams is altered while the drain operation is in progress, and the wait terminates due to a signal interruption or a timeout rather than a normal wake-up event, the cleanup routine finish_wait() is bypassed. Consequently, the stack-allocated wait entry remains queued on the peer stream's sleep list even after the original process context has exited its scope.
The operational impact of this vulnerability is severe, as it leads to a use-after-free scenario that can be exploited by local attackers with access to audio devices or specific system privileges capable of manipulating PCM stream links. When the kernel later attempts to wake up waiters on the affected sleep queue via wake_up(), it iterates through the list of waiting entries. Because the stale entry from the freed stack frame is still present in this list, the kernel dereferences memory that has already been reclaimed and potentially repurposed by other processes or kernel structures. This can result in a system crash leading to denial of service, or more critically, it may allow an attacker to achieve arbitrary code execution by controlling the contents of the freed stack memory prior to its reuse. The vulnerability is reachable through two primary vectors: unlinking either the stream that is currently being drained or the stream that is performing the drain operation against a peer.
The root cause of this issue can be traced back to changes in how read-write locks are managed during PCM link operations and subsequent modifications to wait queue removal logic. Historically, the snd_pcm_link_rwsem was held across the entire wait and removal process, preventing race conditions related to group membership changes. However, a previous optimization removed this lock coverage around the wait period, making the system susceptible to timing windows where stream topology could change mid-operation. Furthermore, the transition from explicit manual removal of wait entries to using finish_wait() inadvertently preserved a conditional logic that only removes the entry if the peer is still found in the caller's group. This design oversight meant that under signal or timeout conditions, which do not trigger automatic removal via autoremove_wake_function(), the stale pointer remained active on the queue.
To mitigate this vulnerability and restore robustness to the PCM subsystem, the fix involves ensuring that all members of a linked stream group are woken up before any changes to their membership status occur. By waking every group member under the protection of the group lock prior to unlinking or modifying the link structure, the draining stream is guaranteed to be released from its wait state while it still maintains valid references and context within the group. This ensures that when the drain operation completes, the associated stack-based wait entry is properly removed before the function returns, thereby preventing the dangling pointer scenario. From a classification perspective, this vulnerability aligns with CWE-416 Use After Free, as it involves accessing memory after it has been freed due to improper lifecycle management of kernel objects. In terms of attack vectors and techniques, this flaw relates to ATT&CK technique T1059 Command and Scripting Interpreter if exploited for privilege escalation via local code execution, or more broadly falls under exploitation of resource management errors that lead to stability compromise. System administrators should ensure their Linux kernels are updated with the patch addressing snd_pcm_drain() logic in the ALSA PCM subsystem to prevent potential remote or local exploitation leading to system instability or unauthorized access.