GHSA-39Q8-GJM7-PM22

Vulnerability from github – Published: 2026-09-16 12:30 – Updated: 2026-10-21 15:41
VLAI
Details

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

ceph: properly decrypt filenames in vmalloc() buffers

The fscrypt subsystem uses the scatterlist crypto API, inheriting its requirement that any buffers are in the linear mapping region. However, the messenger client uses kvmalloc() to create buffers for messages, which will occasionally place those buffers in the vmalloc() region when physical memory fragmentation doesn't permit a large enough kmalloc(). The various callers of ceph_fname_to_usr() directly pass (slices of) raw messages from the MDS without considering that the messages may be in vmalloc() buffers, resulting in oopses especially on non-x86 platforms (see 'Closes:' for more details and a reproducer).

Make ceph_fname_to_usr() explicitly tolerant of vmalloc()-allocated fname->ctext, fname->name, and/or oname->name buffers, using tname (which, when non-null, must be a linear address; when null, is briefly allocated as necessary) as a bounce buffer to avoid passing any inappropriate addresses to fscrypt_fname_disk_to_usr().

Additionally change parse_reply_info_readdir() -- the only function to supply its own tname -- to follow the new "tname must never come from vmalloc()" rule by passing NULL when the message is not in the linear region. Though this causes a per-dentry kmalloc()+kfree(), this overhead exists only when processing the minority of messages that spill into vmalloc(). My (crude) testing puts this at only about 1 in 8,000 readdir messages. Still, if the overhead proves unreasonable in the future, it is easy enough to mitigate: a future change could allocate a bounce buffer in parse_reply_info_readdir() and use that as tname instead.

Severity
9.8 (Critical)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
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{
  "affected": [],
  "aliases": [
    "CVE-2026-90042"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-09-16T11:17:17Z",
    "severity": "CRITICAL"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nceph: properly decrypt filenames in vmalloc() buffers\n\nThe fscrypt subsystem uses the scatterlist crypto API, inheriting its\nrequirement that any buffers are in the linear mapping region. However,\nthe messenger client uses kvmalloc() to create buffers for messages,\nwhich will occasionally place those buffers in the vmalloc() region when\nphysical memory fragmentation doesn\u0027t permit a large enough kmalloc().\nThe various callers of ceph_fname_to_usr() directly pass (slices of) raw\nmessages from the MDS without considering that the messages may be in\nvmalloc() buffers, resulting in oopses especially on non-x86 platforms\n(see \u0027Closes:\u0027 for more details and a reproducer).\n\nMake ceph_fname_to_usr() explicitly tolerant of vmalloc()-allocated\nfname-\u003ectext, fname-\u003ename, and/or oname-\u003ename buffers, using `tname`\n(which, when non-null, must be a linear address; when null, is briefly\nallocated as necessary) as a bounce buffer to avoid passing any\ninappropriate addresses to fscrypt_fname_disk_to_usr().\n\nAdditionally change parse_reply_info_readdir() -- the only function to\nsupply its own `tname` -- to follow the new \"tname must never come from\nvmalloc()\" rule by passing NULL when the message is not in the linear\nregion. Though this causes a per-dentry kmalloc()+kfree(), this overhead\nexists only when processing the minority of messages that spill into\nvmalloc(). My (crude) testing puts this at only about 1 in 8,000 readdir\nmessages. Still, if the overhead proves unreasonable in the future, it\nis easy enough to mitigate: a future change could allocate a bounce\nbuffer in parse_reply_info_readdir() and use that as `tname` instead.",
  "id": "GHSA-39q8-gjm7-pm22",
  "modified": "2026-10-21T15:41:17Z",
  "published": "2026-09-16T12:30:46Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-90042"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/110747ff535e3d98ac17d68dbd056bb6ef000e23"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/23c5cc9652c6ee85617002cb66e1068395045de6"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/3b467c68803d7c7e82678289e598afd44faa6101"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/93729594af506557a86f8b603be7ac5f3370eeca"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/e939fc6a7bd969a58a150b7f188c1047138403e3"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ]
}



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