CVE-2026-74261 (GCVE-0-2026-74261)

Vulnerability from cvelistv5 – Published: 2026-08-15 05:57 – Updated: 2026-08-17 05:16
VLAI
Title
ALSA: seq: avoid stale FIFO cells during resize
Summary
In the Linux kernel, the following vulnerability has been resolved: ALSA: seq: avoid stale FIFO cells during resize snd_seq_fifo_resize() still needs to publish the replacement pool before it waits for FIFO users. A blocking snd_seq_read() holds f->use_lock while it sleeps, so concurrent senders must be able to queue to the new pool and wake that reader instead of failing against a closing old pool. However, snd_seq_fifo_event_in() duplicates an event before it takes f->lock, and snd_seq_read() can dequeue a cell and later call snd_seq_fifo_cell_putback() if copy_to_user() or snd_seq_expand_var_event() fails. If resize swaps f->pool and detaches oldhead in between, either path can relink an old-pool cell after the snapshot. That stale cell sits outside the drained oldhead list, keeps oldpool->counter elevated, and can leave snd_seq_pool_delete() waiting for the retired pool to drain. Keep the existing swap-before-wait ordering in snd_seq_fifo_resize(), but reject stale cells before any FIFO relink. Revalidate event-in cells under f->lock and retry them against the published replacement pool, and free stale putback cells instead of linking them back into the FIFO. The buggy scenario involves two paths, with each column showing the order within that path: resize path: relink path: 1. Allocate newpool. 1. Take f->use_lock. 2. Swap f->pool to newpool and 2. Duplicate or dequeue an old-pool detach oldhead. cell before oldpool closes. 3. Mark oldpool closing and 3. Reach a later relink point after wait for FIFO users. resize published newpool. 4. Free oldhead and delete 4. Relink the old-pool cell after oldpool. resize detached oldhead. 5. Drop f->use_lock. The reproducer reports a resize ioctl blocked in the expected pool teardown path: signal: resize iteration=98 target_pool=4 exceeded 250ms (elapsed=251ms) diagnostic: resize_tid=651 wchan=snd_seq_pool_done diagnostic: resize_tid=651 stack= snd_seq_pool_done+0x5b/0x140 snd_seq_pool_delete+0x7a/0x90 snd_seq_fifo_resize+0x193/0x1e0 snd_seq_ioctl_set_client_pool+0x214/0x260 snd_seq_ioctl+0x119/0x540 __x64_sys_ioctl+0xd1/0x120 do_syscall_64+0xbb/0x2f0 entry_SYSCALL_64_after_hwframe+0x77/0x7f A second run with larger pools hit the same target path: signal: resize iteration=32 target_pool=64 exceeded 250ms (elapsed=251ms) diagnostic: resize_tid=663 wchan=snd_seq_pool_done diagnostic: resize_tid=663 stack= snd_seq_pool_done+0x5b/0x140 snd_seq_pool_delete+0x7a/0x90 snd_seq_fifo_resize+0x193/0x1e0 snd_seq_ioctl_set_client_pool+0x214/0x260 snd_seq_ioctl+0x119/0x540 __x64_sys_ioctl+0xd1/0x120 do_syscall_64+0xbb/0x2f0 entry_SYSCALL_64_after_hwframe+0x77/0x7f
Severity
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 2d7d54002e396c180db0c800c1046f0a3c471597 , < 98a965cb1e767b54b6bbd831b6cea26f521a8f51 (git)
Affected: 2d7d54002e396c180db0c800c1046f0a3c471597 , < 1c4c35fb68d520241f7d9f1c356b5e2370fd8364 (git)
Affected: 2d7d54002e396c180db0c800c1046f0a3c471597 , < e546128291f8d688dcb931827e2efd2aa6c0734d (git)
Affected: df7a2d0af9f7ab73cf22a7b62bbc0bad93a02110 (git)
Affected: 28e0ebdd57cd3287ac821068364b74c70af3861c (git)
Affected: d4b8e8a32d74052fe292618ae19f794944ddc673 (git)
Affected: e91325f27c4d98d1088e9e86b3ab475f752eeb80 (git)
Affected: 9ebfed203c0d93449a074c5c2fd5bb3e58518f0d (git)
Affected: 3492352e1f34673708fa7409b4b1d97545aa2f1c (git)
Affected: a90d7447e4a154ad26e3b9e09a0878680be49339 (git)
Affected: 74a2c1ff88a4e0960623d17f7db56ac5a60bb0cf (git)
Affected: c36ef6467420f8982e6d4d6f93d0634a85a5ee45 (git)
Affected: 3.2.91 , < 3.3 (semver)
Affected: 3.10.107 , < 3.11 (semver)
Affected: 3.12.73 , < 3.13 (semver)
Affected: 3.16.46 , < 3.17 (semver)
Affected: 3.18.50 , < 3.19 (semver)
Affected: 4.1.40 , < 4.2 (semver)
Affected: 4.4.60 , < 4.5 (semver)
Affected: 4.9.21 , < 4.10 (semver)
Affected: 4.10.9 , < 4.11 (semver)
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Linux Linux Affected: 4.11
Unaffected: 0 , < 4.11 (semver)
Unaffected: 6.18.40 , ≤ 6.18.* (semver)
Unaffected: 7.1.5 , ≤ 7.1.* (semver)
Unaffected: 7.2 , ≤ * (original_commit_for_fix)
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      "descriptions": [
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          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nALSA: seq: avoid stale FIFO cells during resize\n\nsnd_seq_fifo_resize() still needs to publish the replacement pool\nbefore it waits for FIFO users. A blocking snd_seq_read() holds\nf-\u003euse_lock while it sleeps, so concurrent senders must be able to\nqueue to the new pool and wake that reader instead of failing against a\nclosing old pool.\n\nHowever, snd_seq_fifo_event_in() duplicates an event before it takes\nf-\u003elock, and snd_seq_read() can dequeue a cell and later call\nsnd_seq_fifo_cell_putback() if copy_to_user() or\nsnd_seq_expand_var_event() fails. If resize swaps f-\u003epool and detaches\noldhead in between, either path can relink an old-pool cell after the\nsnapshot. That stale cell sits outside the drained oldhead list, keeps\noldpool-\u003ecounter elevated, and can leave snd_seq_pool_delete() waiting\nfor the retired pool to drain.\n\nKeep the existing swap-before-wait ordering in snd_seq_fifo_resize(),\nbut reject stale cells before any FIFO relink. Revalidate event-in cells\nunder f-\u003elock and retry them against the published replacement pool, and\nfree stale putback cells instead of linking them back into the FIFO.\n\nThe buggy scenario involves two paths, with each column showing the\norder within that path:\n\nresize path:                    relink path:\n1. Allocate newpool.             1. Take f-\u003euse_lock.\n2. Swap f-\u003epool to newpool and   2. Duplicate or dequeue an old-pool\n   detach oldhead.                  cell before oldpool closes.\n3. Mark oldpool closing and      3. Reach a later relink point after\n   wait for FIFO users.             resize published newpool.\n4. Free oldhead and delete       4. Relink the old-pool cell after\n   oldpool.                         resize detached oldhead.\n                                 5. Drop f-\u003euse_lock.\n\nThe reproducer reports a resize ioctl blocked in the expected pool\nteardown path:\n\nsignal: resize iteration=98 target_pool=4 exceeded 250ms\n        (elapsed=251ms)\ndiagnostic: resize_tid=651 wchan=snd_seq_pool_done\ndiagnostic: resize_tid=651 stack=\n  snd_seq_pool_done+0x5b/0x140\n  snd_seq_pool_delete+0x7a/0x90\n  snd_seq_fifo_resize+0x193/0x1e0\n  snd_seq_ioctl_set_client_pool+0x214/0x260\n  snd_seq_ioctl+0x119/0x540\n  __x64_sys_ioctl+0xd1/0x120\n  do_syscall_64+0xbb/0x2f0\n  entry_SYSCALL_64_after_hwframe+0x77/0x7f\n\nA second run with larger pools hit the same target path:\n\nsignal: resize iteration=32 target_pool=64 exceeded 250ms\n        (elapsed=251ms)\ndiagnostic: resize_tid=663 wchan=snd_seq_pool_done\ndiagnostic: resize_tid=663 stack=\n  snd_seq_pool_done+0x5b/0x140\n  snd_seq_pool_delete+0x7a/0x90\n  snd_seq_fifo_resize+0x193/0x1e0\n  snd_seq_ioctl_set_client_pool+0x214/0x260\n  snd_seq_ioctl+0x119/0x540\n  __x64_sys_ioctl+0xd1/0x120\n  do_syscall_64+0xbb/0x2f0\n  entry_SYSCALL_64_after_hwframe+0x77/0x7f"
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-17T05:16:03.389Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/98a965cb1e767b54b6bbd831b6cea26f521a8f51"
        },
        {
          "url": "https://git.kernel.org/stable/c/1c4c35fb68d520241f7d9f1c356b5e2370fd8364"
        },
        {
          "url": "https://git.kernel.org/stable/c/e546128291f8d688dcb931827e2efd2aa6c0734d"
        }
      ],
      "title": "ALSA: seq: avoid stale FIFO cells during resize",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-74261",
    "datePublished": "2026-08-15T05:57:38.311Z",
    "dateReserved": "2026-08-15T05:44:03.877Z",
    "dateUpdated": "2026-08-17T05:16:03.389Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-74261",
      "date": "2026-10-03",
      "epss": "0.00206",
      "percentile": "0.0965"
    },
    "suse_vex": {
      "aggregate_severity": "moderate",
      "current_release_date": "2026-10-03T00:26:45Z",
      "cve": "CVE-2026-74261",
      "id": "CVE-2026-74261",
      "initial_release_date": "2026-08-26T01:14:20Z",
      "product_status:known_affected": "688",
      "product_status:known_not_affected": "16",
      "product_status:recommended": "168",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-74261",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-74261.json",
      "version": "7"
    }
  }
}



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