# CVE-2026-99271: ALSA: line6: Clear prev_fbuf on capture buffer release

Status: published. Published: 2026-11-07. Updated: 2026-11-07.

In the Linux kernel, the following vulnerability has been resolved:

ALSA: line6: Clear prev_fbuf on capture buffer release

A KASAN slab-use-after-free read was reported in submit_audio_out_urb()
when generating an impulse test signal:

  BUG: KASAN: slab-use-after-free in create_impulse_test_signal sound/usb/line6/playback.c:76 [inline]
  BUG: KASAN: slab-use-after-free in submit_audio_out_urb+0x1848/0x1b20 sound/usb/line6/playback.c:249
  Read of size 2 at addr ffff888008d74870 by task syz.2.3214/7785

  Allocated by task 11:
   kmem_cache_alloc_noprof+0x2f0/0x390 mm/slub.c:4144
   line6_buffer_acquire+0x1a1/0x220 sound/usb/line6/pcm.c:158
   line6_pcm_acquire+0xb6/0x230 sound/usb/line6/pcm.c:329
   line6_startup_work+0x3c/0x50 sound/usb/line6/driver.c:728

  Freed by task 7785:
   kfree+0xf8/0x390 mm/slub.c:6566
   line6_buffer_release sound/usb/line6/pcm.c:176 [inline]
   line6_buffer_release+0xa5/0xf0 sound/usb/line6/pcm.c:170
   __line6_pcm_release sound/usb/line6/pcm.c:305 [inline]
   line6_pcm_release+0x5a/0x80 sound/usb/line6/pcm.c:313
   snd_toneport_monitor_put+0x11b/0x190 sound/usb/line6/toneport.c:183

line6pcm->prev_fbuf points into the capture PCM stream buffer
(line6pcm->in.buffer), which is updated during audio_in_callback() to
feed rate synchronization, software monitoring, and impulse test signal
generation on playback side.

When all capture streams are closed, line6_buffer_release() frees
pstr->buffer with kfree().  However, it does not clear line6pcm->prev_fbuf.
If playback is subsequently started (e.g. via impulse test signal
volume control snd_line6_impulse_volume_put()), submit_audio_out_urb()
dereferences the stale pointer line6pcm->prev_fbuf under in.lock,
resulting in a slab-use-after-free read.

Clear prev_fbuf and prev_fsize in line6_buffer_release() when releasing
the capture stream buffer under in.lock, ensuring that no stale buffer
pointer can be accessed by submit_audio_out_urb().

## Remediation

No remediation reported in collected sources

## Affected products and versions

- Linux / Linux: ≥ 63e20df1e5b2ef8d871ecbdb6c038d554ed1ca74; < 862d9268f40a6e10cef24eb226e738fb69ce8aa7 (affected, git); ≥ 63e20df1e5b2ef8d871ecbdb6c038d554ed1ca74; < 22c82f33ff0b68d37041adf1dea5533a5863cd31 (affected, git); ≥ 63e20df1e5b2ef8d871ecbdb6c038d554ed1ca74; < aa118c8f61d59387961d58ffae831c5259a9f222 (affected, git). Source: CNA: Linux
- Linux / Linux: 4.0 (affected); ≥ 0; < 4.0 (unaffected, semver); ≥ 6.18.61; ≤ 6.18.* (unaffected, semver); ≥ 7.3.2; ≤ 7.3.* (unaffected, semver); ≥ 7.4-rc1; ≤ * (unaffected, original_commit_for_fix). Source: CNA: Linux

## Severity and prioritization

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: Not reported

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://git.kernel.org/stable/c/862d9268f40a6e10cef24eb226e738fb69ce8aa7 (CNA: Linux)

- https://git.kernel.org/stable/c/22c82f33ff0b68d37041adf1dea5533a5863cd31 (CNA: Linux)

- https://git.kernel.org/stable/c/aa118c8f61d59387961d58ffae831c5259a9f222 (CNA: Linux)

## Provenance

- CNA: Linux: https://www.cve.org/CVERecord?id=CVE-2026-99271; retrieved 2026-11-07; source updated 2026-11-07

Revision: 60d12b01b15be6b4c9152c08c13423da06a4b95e3b034eb61938b9d326649e1a

Canonical: https://y2.dev/cve/CVE-2026-99271

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