CVE-2026-80628 in Linux
Summary
by MITRE • 08/28/2026
In the Linux kernel, the following vulnerability has been resolved:
ALSA: seq: oss: Serialize readq reset state with q->lock
snd_seq_oss_readq_clear() resets qlen, head, and tail without q->lock even though the normal reader and producer paths serialize the same ring state under that spinlock. A reset can therefore race snd_seq_oss_readq_free() or snd_seq_oss_readq_put_event() and leave stale records in the queue, drop freshly queued ones, or report the wrong readiness after wakeup. KCSAN reports a data race between snd_seq_oss_readq_clear() and snd_seq_oss_readq_free().
Take q->lock while clearing the ring and resetting input_time. Factor the enqueue logic into a caller-locked helper so snd_seq_oss_readq_put_timestamp() updates its suppression state under the same lock instead of racing the reset path.
The buggy scenario involves two paths, with each column showing the order within that path:
reset path: locked readq updater: 1. snd_seq_oss_reset() or 1. A reader or callback producer release reaches takes q->lock on the same queue. snd_seq_oss_readq_clear(). 2. snd_seq_oss_readq_clear() 2. The updater tests or modifies resets qlen, head, tail, qlen, head, and tail. and input_time. 3. snd_seq_oss_readq_clear() 3. The updater completes its wakes sleepers on read-modify-write sequence. q->midi_sleep. 4. Without q->lock, the reset 4. The resulting ring state drives can overlap the locked later reads and readiness. update.
KCSAN reports:
BUG: KCSAN: data-race in snd_seq_oss_readq_clear / snd_seq_oss_readq_free
write to 0xffff8881069fe608 of 4 bytes by task 120516 on cpu 0: snd_seq_oss_readq_free+0x6c/0x80 snd_seq_oss_read+0xcb/0x250 odev_read+0x38/0x60 vfs_read+0xff/0x600 ksys_read+0xb4/0x140 __x64_sys_read+0x46/0x60 do_syscall_64+0xbb/0x2f0 entry_SYSCALL_64_after_hwframe+0x77/0x7f
read to 0xffff8881069fe608 of 4 bytes by task 120517 on cpu 1: snd_seq_oss_readq_clear+0x1f/0x90 snd_seq_oss_reset+0xa7/0xf0 snd_seq_oss_ioctl+0x6f6/0x7e0 odev_ioctl+0x56/0xc0 __x64_sys_ioctl+0xd1/0x120 do_syscall_64+0xbb/0x2f0 entry_SYSCALL_64_after_hwframe+0x77/0x7f
value changed: 0x00000001 -> 0x00000000
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Analysis
by VulDB Data Team • 08/28/2026
The Linux kernel's Advanced Linux Sound Architecture (ALSA) subsystem contains a concurrency vulnerability within the OSS compatibility layer, specifically affecting the sequence read queue management. The core issue resides in the snd_seq_oss_readq_clear function, which is responsible for resetting the ring buffer state by clearing length, head, and tail pointers as well as input time metrics. This operation was previously executed without acquiring the q->lock spinlock that governs access to these shared data structures. In contrast, the standard producer path via snd_seq_oss_readq_put_event and the consumer path via snd_seq_oss_readq_free both correctly serialize their modifications under this same lock. The absence of synchronization in the reset path creates a classic race condition where concurrent execution can lead to inconsistent state transitions within the ring buffer infrastructure.
This lack of mutual exclusion allows for data races between the reset operation and active read or free operations performed by other threads. When snd_seq_oss_readq_clear executes concurrently with snd_seq_oss_readq_free, it modifies shared memory locations such as queue length pointers without atomic guarantees. Kernel Concurrency Sanitizer (KCSAN) has identified this specific race condition, highlighting a write to the ring buffer state from the reset path conflicting with reads or modifications in the free path. The operational impact of this flaw includes potential corruption of internal queue structures, leading to stale records remaining in the queue after a reset, loss of newly queued events due to overwritten pointers, and incorrect readiness states reported to user-space applications following wake-up sequences. Such inconsistencies can cause audio processing errors, application crashes, or unpredictable behavior in systems relying on precise timing and data integrity within ALSA OSS emulation layers.
From a vulnerability classification perspective, this defect aligns with CWE-362, which describes concurrent execution using shared resources with improper synchronization. The race condition allows one thread to interfere with the state of another by modifying critical variables outside the protected section defined by the spinlock. Furthermore, in the context of the MITRE ATT&CK framework for Linux systems, this scenario reflects techniques associated with resource manipulation and potential denial of service through instability or data corruption within kernel subsystems. Although primarily a stability issue rather than an immediate privilege escalation vector, such race conditions can sometimes be leveraged to trigger undefined behavior that might lead to memory safety violations if the corrupted state is subsequently dereferenced in unexpected ways.
The remediation strategy implemented involves enforcing strict serialization by acquiring q->lock during the execution of snd_seq_oss_readq_clear. This ensures that all modifications to qlen, head, tail, and input_time are atomic with respect to other operations on the same queue. Additionally, the enqueue logic was refactored into a caller-locked helper function. This structural change allows snd_seq_oss_readq_put_timestamp to update its suppression state under the protection of q->lock, thereby eliminating races between timestamp updates and reset operations. By ensuring that all paths accessing or modifying the ring buffer state operate within the same critical section, the kernel maintains data integrity and prevents the interleaving of conflicting read-modify-write sequences. This fix restores the expected deterministic behavior of the ALSA OSS sequence interface under concurrent load conditions.