{
  "schema_version": "1.6.1",
  "id": "RPI-CVE-2026-89639",
  "modified": "2026-10-09T11:39:44Z",
  "upstream": [
    "CVE-2026-89639"
  ],
  "published": "2026-09-11T19:47:07Z",
  "summary": "cifs: use cifs_invalidate_cache() in cifs_do_truncate() for O_TRUNC",
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\ncifs: use cifs_invalidate_cache() in cifs_do_truncate() for O_TRUNC\n\ncifs_do_truncate() is invoked from cifs_open() without i_rwsem, so it\ncannot use cifs_resize_file_locked() to perform a proper fscache cookie\nresize.  Instead, add cifs_invalidate_cache() after cifs_setsize().\n\ncifs_invalidate_cache() calls fscache_invalidate(), which works without\nholding i_rwsem: it unconditionally increments inval_counter and sets\nFSCACHE_COOKIE_NO_DATA_TO_READ, ensuring that stale cached data is not\nserved once the cookie is later activated by fscache_use_cookie().\nTruncation to zero leaves no valid cached data, making invalidation the\ncorrect semantic here.",
  "severity": [
    {
      "type": "CVSS_V3",
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N"
    }
  ],
  "affected": [
    {
      "package": {
        "ecosystem": "Raspberry Pi OS:12",
        "name": "linux"
      },
      "versions": [
        "1:6.12.109-1+rpt1"
      ],
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "linux-image-6.12.109+rpt-rpi-2712",
            "binary_version": "1:6.12.109-1+rpt1"
          },
          {
            "binary_name": "linux-image-6.12.109+rpt-rpi-v6",
            "binary_version": "1:6.12.109-1+rpt1"
          },
          {
            "binary_name": "linux-image-6.12.109+rpt-rpi-v7",
            "binary_version": "1:6.12.109-1+rpt1"
          },
          {
            "binary_name": "linux-image-6.12.109+rpt-rpi-v7l",
            "binary_version": "1:6.12.109-1+rpt1"
          },
          {
            "binary_name": "linux-image-6.12.109+rpt-rpi-v8",
            "binary_version": "1:6.12.109-1+rpt1"
          },
          {
            "binary_name": "linux-image-6.12.109+rpt-rpi-v8-rt",
            "binary_version": "1:6.12.109-1+rpt1"
          }
        ]
      },
      "database_specific": {
        "per_version": {
          "1:6.12.109-1+rpt1": {
            "linux_commit": "7d1826930811232688a50c99c540fbb137aed081",
            "upstream_version": "6.12.109",
            "assessment": "commit ancestry (strak rule)",
            "upstream_fixed": null
          }
        }
      }
    }
  ],
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://www.cve.org/CVERecord?id=CVE-2026-89639"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/8b9b10fe5b8b492b27b9f4546742ea541a650213"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/81fc3868a7f726980ff845c1d0d271051e5f0f45"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/364b183230586a62660a7280c1eb20138338eeb5"
    }
  ],
  "database_specific": {
    "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git",
    "upstream_modified": "2026-09-13T06:49:25Z",
    "severity": {
      "source": "kernel CNA",
      "cvss_v3_score": 7.1,
      "cvss_v3_severity": "High",
      "scenario": "AV:L - cifs_do_truncate() runs from cifs_open() on the SMB client during a local open/openat with O_TRUNC on a mounted CIFS share (fs/smb/client/), not from ksmbd/nfsd or demux-thread packet parsing; a remote SMB peer cannot invoke this path.\nAC:L - A write-capable open with O_TRUNC deterministically skips fscache invalidation, then the same cifs_open() activates the cookie via fscache_use_cookie(); the attacker can also hold another fd so the cookie is already active, with no race or layout outside their control.\nPR:L - O_TRUNC requires only MAY_WRITE on the target inode, which an ordinary local user has on an already-mounted CIFS share; no init-namespace root, CAP_SYS_ADMIN, or user-namespace mount of CIFS is needed.\nUI:N - The attacker issues open(O_TRUNC) and follow-on reads/writes themselves; on common fstab/autofs/CIFS-home deployments with the fsc option already set, no other user must mount the share or open the file.\nS:U - Stale data stays within the local CIFS client's fscache and the same SMB file's contents; this is not a VM escape, IOMMU bypass, or other cross-authority boundary crossing.\nC:H - After O_TRUNC the cookie is activated without FSCACHE_COOKIE_NO_DATA_TO_READ, so later reads (including holes after a size-extending write) can return the full previously truncated file contents that should have been discarded.\nI:H - The same stale cookie presents discarded bytes as current file data and can persist them to the SMB server via netfs read-modify-write/writeback, fully replacing zeros or newly written contents on that file.\nA:N - The flaw is fscache coherency only; it does not oops, panic, deadlock, or exhaust kernel resources, so host availability is unaffected."
    }
  }
}