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CVE-2026-89595 (GCVE-0-2026-89595)

Vulnerability from cvelistv5 – Published: 2026-09-11 19:44 – Updated: 2026-09-14 12:01
VLAI
Title
fsnotify: Fix stale object mask after concurrent mark updates
Summary
In the Linux kernel, the following vulnerability has been resolved: fsnotify: Fix stale object mask after concurrent mark updates When a mark gets a new event bit, fanotify and inotify may avoid recalculating the object mask if the cached aggregate already contains that bit. This is racy with a recalculation triggered by a concurrent update to another mark on the same connector. The concurrent scan can read the mark before the new bit is added, while the updater reads the old aggregate before that scan publishes its result. The updater then skips recalculation and the scan publishes a mask without the bit, leaving the object mask stale after both updates complete. This can be reproduced with two fanotify groups watching the same inode: one thread removes FAN_MODIFY from one existing mark while another thread adds FAN_MODIFY to the other mark. After both fanotify_mark() calls return, writes can fail to produce FAN_MODIFY for the group whose mark now contains the bit. This was reproduced on an unmodified v6.12.95 kernel. The equivalent inotify interleaving loses IN_MODIFY events. For normal fanotify additions, recalculate whenever the raw mark mask changes. The normal mask is not cleared asynchronously, so an unchanged addition cannot introduce missing interest. Always recalculate ignore-mask updates because FS_MODIFY handling may clear the ignore mask without taking mark->lock, making snapshot comparisons unreliable. Always recalculate after updating an existing inotify watch. Its replace path temporarily sets mark->mask to zero, so a concurrent scan can observe zero even when the old and final masks are equal. Assigning the replacement mask directly would avoid the transient zero, but existing-watch updates are infrequent, so unconditional recalculation is simpler.
Severity
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 63c882a05416e18de6fb59f7dd6da48f3bbe8273 , < 27d172b60eeca5c8fd51b246f9fb959067cf102b (git)
Affected: 63c882a05416e18de6fb59f7dd6da48f3bbe8273 , < 2f09f08d602647fc4e328fc27ecb4c3008d10338 (git)
Affected: 63c882a05416e18de6fb59f7dd6da48f3bbe8273 , < de75382d6e354b2b055df4896d12a91969f12090 (git)
Affected: 63c882a05416e18de6fb59f7dd6da48f3bbe8273 , < 343ae18e960f6c5f1d34d58a69750c62cd463228 (git)
Affected: 63c882a05416e18de6fb59f7dd6da48f3bbe8273 , < 92289e66639f62abc754c6f3bce5ead7e98e4ee2 (git)
Affected: 63c882a05416e18de6fb59f7dd6da48f3bbe8273 , < 947400af98b9e63841929d079a2c3ea0a8ba227b (git)
Affected: 63c882a05416e18de6fb59f7dd6da48f3bbe8273 , < ac8d8b599d466a129122bded77db3d0f8b96b461 (git)
Affected: 63c882a05416e18de6fb59f7dd6da48f3bbe8273 , < e422777fdd4746de1109575c51e65038d4c5c1be (git)
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Linux Linux Affected: 2.6.31
Unaffected: 0 , < 2.6.31 (semver)
Unaffected: 5.10.270 , ≤ 5.10.* (semver)
Unaffected: 5.15.221 , ≤ 5.15.* (semver)
Unaffected: 6.1.188 , ≤ 6.1.* (semver)
Unaffected: 6.6.157 , ≤ 6.6.* (semver)
Unaffected: 6.12.110 , ≤ 6.12.* (semver)
Unaffected: 6.18.51 , ≤ 6.18.* (semver)
Unaffected: 7.2.4 , ≤ 7.2.* (semver)
Unaffected: 7.3-rc1 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nfsnotify: Fix stale object mask after concurrent mark updates\n\nWhen a mark gets a new event bit, fanotify and inotify may avoid\nrecalculating the object mask if the cached aggregate already contains that\nbit. This is racy with a recalculation triggered by a concurrent update to\nanother mark on the same connector.\n\nThe concurrent scan can read the mark before the new bit is added, while\nthe updater reads the old aggregate before that scan publishes its result.\nThe updater then skips recalculation and the scan publishes a mask without\nthe bit, leaving the object mask stale after both updates complete.\n\nThis can be reproduced with two fanotify groups watching the same inode:\none thread removes FAN_MODIFY from one existing mark while another thread\nadds FAN_MODIFY to the other mark. After both fanotify_mark() calls return,\nwrites can fail to produce FAN_MODIFY for the group whose mark now contains\nthe bit. This was reproduced on an unmodified v6.12.95 kernel. The\nequivalent inotify interleaving loses IN_MODIFY events.\n\nFor normal fanotify additions, recalculate whenever the raw mark mask\nchanges. The normal mask is not cleared asynchronously, so an unchanged\naddition cannot introduce missing interest. Always recalculate ignore-mask\nupdates because FS_MODIFY handling may clear the ignore mask without taking\nmark-\u003elock, making snapshot comparisons unreliable.\n\nAlways recalculate after updating an existing inotify watch. Its replace\npath temporarily sets mark-\u003emask to zero, so a concurrent scan can observe\nzero even when the old and final masks are equal. Assigning the replacement\nmask directly would avoid the transient zero, but existing-watch updates\nare infrequent, so unconditional recalculation is simpler."
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        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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          "url": "https://git.kernel.org/stable/c/e422777fdd4746de1109575c51e65038d4c5c1be"
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-89595",
    "datePublished": "2026-09-11T19:44:58.057Z",
    "dateReserved": "2026-09-11T19:38:34.730Z",
    "dateUpdated": "2026-09-14T12:01:18.174Z",
    "state": "PUBLISHED"
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This is racy with a recalculation triggered by a concurrent update to\\nanother mark on the same connector.\\n\\nThe concurrent scan can read the mark before the new bit is added, while\\nthe updater reads the old aggregate before that scan publishes its result.\\nThe updater then skips recalculation and the scan publishes a mask without\\nthe bit, leaving the object mask stale after both updates complete.\\n\\nThis can be reproduced with two fanotify groups watching the same inode:\\none thread removes FAN_MODIFY from one existing mark while another thread\\nadds FAN_MODIFY to the other mark. After both fanotify_mark() calls return,\\nwrites can fail to produce FAN_MODIFY for the group whose mark now contains\\nthe bit. This was reproduced on an unmodified v6.12.95 kernel. The\\nequivalent inotify interleaving loses IN_MODIFY events.\\n\\nFor normal fanotify additions, recalculate whenever the raw mark mask\\nchanges. The normal mask is not cleared asynchronously, so an unchanged\\naddition cannot introduce missing interest. Always recalculate ignore-mask\\nupdates because FS_MODIFY handling may clear the ignore mask without taking\\nmark-\u003elock, making snapshot comparisons unreliable.\\n\\nAlways recalculate after updating an existing inotify watch. Its replace\\npath temporarily sets mark-\u003emask to zero, so a concurrent scan can observe\\nzero even when the old and final masks are equal. 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    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-09-16T12:14:03+00:00",
      "cve": "CVE-2026-89595",
      "id": "CVE-2026-89595",
      "initial_release_date": "2026-09-11T00:00:00+00:00",
      "product_status:known_affected": "2",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: fsnotify: Fix stale object mask after concurrent mark updates",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89595.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "low",
      "current_release_date": "2026-09-12T16:25:29Z",
      "cve": "CVE-2026-89595",
      "id": "CVE-2026-89595",
      "initial_release_date": "2026-09-12T16:25:29Z",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-89595",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-89595.json",
      "version": "2"
    }
  }
}



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  • Confirmed: The vulnerability has been validated from an analyst's perspective.
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