HIGH Introduced in 2.6.12
seq/oss Readq Race
CVE-2026-80628
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
KernelScan AI3.6LOW
01Description
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
02KernelScan AI Analysis
Risk summary
A local user with access to the OSS sequencer device can trigger a data race by concurrently resetting and reading the sequencer's ring buffer, corrupting internal queue state. The impact is limited to degraded sequencer functionality—stale events, dropped events, or incorrect readiness—without kernel memory disclosure or code execution. Products that do not expose /dev/sequencer to untrusted users are not at risk.
Vulnerability analysis
The ALSA OSS sequencer's queue-clear function resets the ring-buffer length and head/tail indices without holding the queue spinlock, while the normal reader and producer paths modify those same fields under that lock. A concurrent reset can therefore interleave with a locked update and corrupt the ring-buffer state, leaving stale events in the queue, dropping freshly queued ones, or reporting incorrect readiness to waiting readers. The fix acquires the queue lock before clearing the ring buffer and refactors the enqueue logic into a caller-locked helper so that timestamp-based event insertion also updates its suppression state under the same lock. The vulnerability is reachable locally by any user with access to the OSS sequencer device node, and exploitation requires two threads racing on the same device file descriptor.
Lifecycle
03Fix Versions
| Branch | Introduced | Fixed in | Patch commit |
|---|---|---|---|
| 6.18 | 2.6.12 | 6.18.40 | 287d506d4e08 |
| 7.1 | 2.6.12 | 7.1.5 | 43e10709b1ba |
| mainline | 2.6.12 | 7.2 | 49ce92d20782 |