CVE-2026-99084 (GCVE-0-2026-99084)

Vulnerability from cvelistv5 – Published: 2026-10-23 12:45 – Updated: 2026-10-23 12:45
VLAI
Title
readdir: take no inode lock on an immutable directory
Summary
In the Linux kernel, the following vulnerability has been resolved: readdir: take no inode lock on an immutable directory iterate_dir() takes the directory's i_rwsem shared and holds it across ->iterate_shared(). For a directory that never has an entry and is never removed the lock keeps nothing still, it only orders every reader and every writer of that inode behind each other. For the directory of a nullfs instance that matters. The instance of the initial mount namespace is the root of every empty mount namespace and the private instance is the root of every kernel thread, so one inode is shared across users who have nothing else in common. And a reader can hold the lock for as long as it likes: back the getdents() buffer with a mapping of a file on a FUSE mount of your own, let the copy of "." and ".." fault and let the server wait. Queue an exclusive taker behind it, a mkdir() in that directory goes through start_dirop() before the read-only mount is reported, and from then on every lookup that misses the dcache in that directory, every create and every mount on it waits until the server answers. One user of an empty mount namespace stalls all the others. Add FOP_IMMUTABLE for the file operations of a directory that never changes and is never removed and let iterate_dir() skip the lock for it. The flag never changes for a file, ->f_pos is protected by f_pos_lock since directories are FMODE_ATOMIC_POS, IS_DEADDIR can't be set on such a directory and neither touch_atime() nor fsnotify take i_rwsem. Set it on the nullfs directory. The placeholder directories of libfs never have an entry either but their owners remove them, so they keep the lock.
Severity
No CVSS data available.
Assigner
Linux CNA under the mitre root
CNA scorecard D 53/100 over 6971 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 9d4e752a24f740b31ca827bfab07010e4e7f34b0 , < 6d30b399ae28e5166d62484f81ccaefde6fe7996 (git)
Affected: 9d4e752a24f740b31ca827bfab07010e4e7f34b0 , < e08f57a7dcb83818c058e415988c23beb6c5a47f (git)
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Linux Linux Affected: 7.1
Unaffected: 0 , < 7.1 (semver)
Unaffected: 7.2.12 , ≤ 7.2.* (semver)
Unaffected: 7.3 , ≤ * (original_commit_for_fix)
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{
  "containers": {
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          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/nullfs.c",
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        }
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      "providerMetadata": {
        "dateUpdated": "2026-10-23T12:45:02.631Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
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          "url": "https://git.kernel.org/stable/c/e08f57a7dcb83818c058e415988c23beb6c5a47f"
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      "title": "readdir: take no inode lock on an immutable directory",
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    "datePublished": "2026-10-23T12:45:02.631Z",
    "dateReserved": "2026-09-25T10:25:14.390Z",
    "dateUpdated": "2026-10-23T12:45:02.631Z",
    "state": "PUBLISHED"
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      "percentile": "0.0376"
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          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nreaddir: take no inode lock on an immutable directory\n\niterate_dir() takes the directory\u0027s i_rwsem shared and holds it across\n-\u003eiterate_shared(). For a directory that never has an entry and is\nnever removed the lock keeps nothing still, it only orders every reader\nand every writer of that inode behind each other.\n\nFor the directory of a nullfs instance that matters. The instance of\nthe initial mount namespace is the root of every empty mount namespace\nand the private instance is the root of every kernel thread, so one\ninode is shared across users who have nothing else in common. And a\nreader can hold the lock for as long as it likes: back the getdents()\nbuffer with a mapping of a file on a FUSE mount of your own, let the\ncopy of \".\" and \"..\" fault and let the server wait. Queue an exclusive\ntaker behind it, a mkdir() in that directory goes through start_dirop()\nbefore the read-only mount is reported, and from then on every lookup\nthat misses the dcache in that directory, every create and every mount\non it waits until the server answers. One user of an empty mount\nnamespace stalls all the others.\n\nAdd FOP_IMMUTABLE for the file operations of a directory that never\nchanges and is never removed and let iterate_dir() skip the lock for\nit. The flag never changes for a file, -\u003ef_pos is protected by\nf_pos_lock since directories are FMODE_ATOMIC_POS, IS_DEADDIR can\u0027t be\nset on such a directory and neither touch_atime() nor fsnotify take\ni_rwsem. Set it on the nullfs directory. The placeholder directories of\nlibfs never have an entry either but their owners remove them, so they\nkeep the lock."
          }
        ],
        "id": "CVE-2026-99084",
        "lastModified": "2026-10-23T13:17:32.693",
        "metrics": {},
        "published": "2026-10-23T13:17:32.693",
        "references": [
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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      "cve": "CVE-2026-99084",
      "id": "CVE-2026-99084",
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      "product_status:known_affected": "14",
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      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: readdir: take no inode lock on an immutable directory",
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      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/2026/cve-2026-99084.json",
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    }
  }
}



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