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ALSA: pcm: Fix potential AB/BA lock with buffer_mutex and mmap_lock

Type: advisorySources: OSV

In the Linux kernel, the following vulnerability has been resolved: ALSA: pcm: Fix potential AB/BA lock with buffer_mutex and mmap_lock syzbot caught a potential deadlock between the PCM runtime->buffer_mutex and the mm->mmap_lock. It was brought by the recent fix to cover the racy read/write and other ioctls, and in that commit, I overlooked a (hopefully only) corner case that may take the revert lock, namely, the OSS mmap. The OSS mmap operation exceptionally allows to re-configure the parameters inside the OSS mmap syscall, where mm->mmap_mutex is already held. Meanwhile, the copy_from/to_user calls at read/write operations also take the mm->mmap_lock internally, hence it may lead to a AB/BA deadlock. A similar problem was already seen in the past and we fixed it with a refcount (in commit b248371628aa). The former fix covered only the call paths with OSS read/write and OSS ioctls, while we need to cover the concurrent access via both ALSA and OSS APIs now. This patch addresses the problem above by replacing the buffer_mutex lock in the read/write operations with a refcount similar as we've used for OSS. The new field, runtime->buffer_accessing, keeps the number of concurrent read/write operations. Unlike the former buffer_mutex protection, this protects only around the copy_from/to_user() calls; the other codes are basically protected by the PCM stream lock. The refcount can be a negative, meaning blocked by the ioctls. If a negative value is seen, the read/write aborts w

Products
Kernel
Affected versions
Not specified
Fixed versions
5.10.110, 5.15.33, 5.16.19, 5.17.2
CVEs
CVE-2022-49272
Confirmed fixed CVEs
Not specified
Updated in this feed
4 Nov 2026, 16:14 UTC · Revision 1

Source evidence

ALSA: pcm: Fix potential AB/BA lock with buffer_mutex and mmap_lock

core-osv · Original source

Published 26 Feb 2025, 01:56 UTC

In the Linux kernel, the following vulnerability has been resolved: ALSA: pcm: Fix potential AB/BA lock with buffer_mutex and mmap_lock syzbot caught a potential deadlock between the PCM runtime->buffer_mutex and the mm->mmap_lock. It was brought by the recent fix to cover the racy read/write and other ioctls, and in that commit, I overlooked a (hopefully only) corner case that may take the revert lock, namely, the OSS mmap. The OSS mmap operation exceptionally allows to re-configure the parameters inside the OSS mmap syscall, where mm->mmap_mutex is already held. Meanwhile, the copy_from/to_user calls at read/write operations also take the mm->mmap_lock internally, hence it may lead to a AB/BA deadlock. A similar problem was already seen in the past and we fixed it with a refcount (in commit b248371628aa). The former fix covered only the call paths with OSS read/write and OSS ioctls, while we need to cover the concurrent access via both ALSA and OSS APIs now. This patch addresses the problem above by replacing the buffer_mutex lock in the read/write operations with a refcount similar as we've used for OSS. The new field, runtime->buffer_accessing, keeps the number of concurrent read/write operations. Unlike the former buffer_mutex protection, this protects only around the copy_from/to_user() calls; the other codes are basically protected by the PCM stream lock. The refcount can be a negative, meaning blocked by the ioctls. If a negative value is seen, the read/write aborts w

osv:CVE-2022-49272

Kernel

Fixed versions: 5.10.110, 5.15.33, 5.16.19, 5.17.2

Complete source record
{
  "id": "1bac41bd695aec0c40af5fc18f64b195b1f28ea96defbf14e6e29fe3a3cd8651",
  "url": "https://osv.dev/vulnerability/CVE-2022-49272",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "ALSA: pcm: Fix potential AB/BA lock with buffer_mutex and mmap_lock",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: ALSA: pcm: Fix potential AB/BA lock with buffer_mutex and mmap_lock syzbot caught a potential deadlock between the PCM runtime->buffer_mutex and the mm->mmap_lock. It was brought by the recent fix to cover the racy read/write and other ioctls, and in that commit, I overlooked a (hopefully only) corner case that may take the revert lock, namely, the OSS mmap. The OSS mmap operation exceptionally allows to re-configure the parameters inside the OSS mmap syscall, where mm->mmap_mutex is already held. Meanwhile, the copy_from/to_user calls at read/write operations also take the mm->mmap_lock internally, hence it may lead to a AB/BA deadlock. A similar problem was already seen in the past and we fixed it with a refcount (in commit b248371628aa). The former fix covered only the call paths with OSS read/write and OSS ioctls, while we need to cover the concurrent access via both ALSA and OSS APIs now. This patch addresses the problem above by replacing the buffer_mutex lock in the read/write operations with a refcount similar as we've used for OSS. The new field, runtime->buffer_accessing, keeps the number of concurrent read/write operations. Unlike the former buffer_mutex protection, this protects only around the copy_from/to_user() calls; the other codes are basically protected by the PCM stream lock. The refcount can be a negative, meaning blocked by the ioctls. If a negative value is seen, the read/write aborts w",
    "evidence": "osv:CVE-2022-49272",
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    "severity": "unknown",
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      "modified": "2026-10-28T02:30:37.597511288Z",
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    "related_cves": [
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    "security_relevant": true,
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  },
  "source_id": "core-osv",
  "document_id": 504547,
  "published_at": "2025-02-26T01:56:18.626+00:00"
}