CVE-2026-89648: Software Security Vulnerability Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-2j45-hm4h-36gr",
  "modified" : "2026-09-13T09:32:26Z",
  "published" : "2026-09-11T21:31:35Z",
  "aliases" : [ "CVE-2026-89648" ],
  "details" : "In the Linux kernel, the following vulnerability has been resolved:\n\nceph: cap delegated inode count in ceph_parse_deleg_inos()\n\nceph_parse_deleg_inos() decodes interval sets of delegated inode numbers\nfrom an MDS create-with-delegation reply. For each set it reads a 64-bit\nstart and a 64-bit len with ceph_decode_64_safe(), which only validates\nthat the eight bytes are present in the message, not the value, and then\nloops over len while inserting entries into s_delegated_inos.\n\nlen is fully attacker controlled. A malicious or compromised MDS can send\none huge interval, many intervals in one reply, duplicate intervals, or\nrepeated replies that accumulate delegated inodes on the same session.\nThe original code bounded none of these and could spin the insert loop or\ngrow the xarray without limit.\n\nBound both dimensions with a single enforcement point. Track the number\nof delegated inodes held by each MDS session in an atomic counter and\ngrow it only in ceph_insert_deleg_ino(), which uses atomic_add_unless()\nto refuse to push the count past CEPH_MAX_DELEG_INOS. Because that helper\nis the only place the counter grows, the per-session population can never\nexceed the cap, so no separate per-session pre-check is needed. The\ncounter is decremented when async create consumes a delegated inode or\nwhen an insert fails, incremented when a delegated inode is restored,\ninitialized with the session xarray, and reset when reconnect destroys\nthe xarray.\n\nA per-session cap alone still lets one reply spin the insert loop on\nduplicate ranges without growing the counter, so also cap the aggregate\ninterval length accepted from a single reply. Together these bound both\nthe loop trip count per reply and the xarray population across replies.\n\nThe cap is a fixed, client-chosen constant rather than a value derived\nfrom the MDS. mds_client_prealloc_inos is a userspace MDS configuration\noption; it is never sent to the kernel client on the wire, and a\nserver-supplied bound could not be trusted for a defensive limit in any\ncase. The constant is set well above that option's documented default of\n1000 (a generous multiple), so legitimate refill behavior is unaffected\nwhile the CPU and xarray memory a malformed delegation stream can consume\nstays bounded.\n\nImpact: a malicious or compromised Ceph MDS can no longer make a client\nspin through an unbounded delegated-inode interval or grow one session's\ndelegated-inode xarray without limit.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
  } ],
  "affected" : [ ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-89648"
  }, {
    "type" : "WEB",
    "url" : "https://git.kernel.org/stable/c/4bd3158bd62466d57ed72a3f7bc5f205fedd6919"
  }, {
    "type" : "WEB",
    "url" : "https://git.kernel.org/stable/c/c040e139f1a629b767f900bbbc3f9892c290ed85"
  }, {
    "type" : "WEB",
    "url" : "https://git.kernel.org/stable/c/f341270ac5f5077804d7837ce77b0f0df1cea29d"
  } ],
  "database_specific" : {
    "cwe_ids" : [ ],
    "severity" : "HIGH",
    "github_reviewed" : false,
    "github_reviewed_at" : null,
    "nvd_published_at" : "2026-09-11T20:19:50Z"
  }
}