{
  "affected": [
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:12",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:13",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:14",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "details": "In the Linux kernel, the following vulnerability has been resolved:  ocfs2: validate rl_used against rl_count in refcount block validator  ocfs2_find_refcount_rec_in_rl() walks the on-disk refcount record array with:  \tfor (; i \u003c le16_to_cpu(rb-\u003erf_records.rl_used); i++) { \t\trec = \u0026rb-\u003erf_records.rl_recs[i]; \t\t...  rl_recs[] lives in a single metadata block (4096 bytes on the common configuration), so its real capacity is fixed by ocfs2_refcount_recs_per_rb(sb) (247 records for a 4K block with the 16-byte ocfs2_refcount_rec).  rl_used and rl_count are both read directly off disk by ocfs2_validate_refcount_block() and are never checked against that capacity, nor against each other, before any refcount/reflink/CoW operation walks the array.  A crafted (or corrupted) refcount block with rl_used == 0xffff makes the loop above walk far past the end of the block, dereferencing rl_recs[i] for i up to 65534.  The resulting index is then handed to the sibling ocfs2_insert_refcount_rec(), whose insert-shift does:  \tif (index \u003c le16_to_cpu(rf_list-\u003erl_used)) \t\tmemmove(\u0026rf_list-\u003erl_recs[index + 1], \t\t\t\u0026rf_list-\u003erl_recs[index], \t\t\t(le16_to_cpu(rf_list-\u003erl_used) - index) * \t\t\t sizeof(struct ocfs2_refcount_rec));  i.e.  a memmove() of up to (0xffff - index) * 16 bytes (~1 MiB) from an offset already past the block.  This is reachable from an ordinary reflink (FICLONE) against a crafted/corrupted ocfs2 image: attaching an extent whose cpos sorts past every real record in the leaf forces the lookup to run off the end instead of returning early on a match.  The attacker model is local: CAP_SYS_ADMIN mounting a crafted or corrupted ocfs2 image, or a raw write to the block device backing an already-mounted ocfs2 filesystem.  ocfs2_validate_refcount_block() already validates the block's ECC, signature, rf_blkno and rf_fs_generation, but never rl_count/rl_used against the block's actual on-disk capacity.  This is the same class of gap that ocfs2_validate_extent_block() (fs/ocfs2/alloc.c) already closes for the sibling extent-list header, which checks both the record capacity and the \"used\" bound before any code walks h_list.l_recs[]:  \tif (le16_to_cpu(eb-\u003eh_list.l_count) != ocfs2_extent_recs_per_eb(sb)) { \t\trc = ocfs2_error(...); \t\tgoto bail; \t}  \tif (le16_to_cpu(eb-\u003eh_list.l_next_free_rec) \u003e \t    le16_to_cpu(eb-\u003eh_list.l_count)) { \t\trc = ocfs2_error(...); \t\tgoto bail; \t}  Add the equivalent pair of checks to ocfs2_validate_refcount_block(): reject a refcount block whose rl_count does not match the fixed per-block capacity returned by ocfs2_refcount_recs_per_rb(), and reject rl_used \u003e rl_count.  Both checks are skipped when OCFS2_REFCOUNT_TREE_FL is set, because in that case the same union bytes hold an ocfs2_extent_list (rf_list), not the refcount record list (rf_records) -- that layout is already validated separately by ocfs2_validate_extent_block() when the referenced extent block is read.  This mirrors the existing \"!(rb-\u003erf_flags \u0026 OCFS2_REFCOUNT_TREE_FL)\" guard used elsewhere in this file (e.g.  ocfs2_get_refcount_rec()) to decide whether rf_records or rf_list is the live member of the union.  With this in place, a forged rl_used/rl_count is caught at block validation time (ocfs2_error()), consistent with every other corruption check in this function, instead of driving an out-of-bounds read in ocfs2_find_refcount_rec_in_rl() and a subsequent out-of-bounds memmove() in ocfs2_insert_refcount_rec().  Verified against a crafted image on a v6.19 KASAN (KASAN_GENERIC) build: replaying the same reflink (FICLONE) reliably hit a KASAN report in __ocfs2_increase_refcount()/ocfs2_insert_refcount_rec() before this patch, and triggers no report once ocfs2_validate_refcount_block() rejects the forged rl_used/rl_count.",
  "id": "DEBIAN-CVE-2026-89493",
  "modified": "2026-09-15T08:47:37.958625964Z",
  "published": "2026-09-11T20:19:31.220Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://security-tracker.debian.org/tracker/CVE-2026-89493"
    }
  ],
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "upstream": [
    "CVE-2026-89493"
  ]
}