{
  "affected": [
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:14",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "7.0.12-1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "details": "In the Linux kernel, the following vulnerability has been resolved:  mm/rmap: initialize nr_pages to 1 at loop start in try_to_unmap_one  Initialize nr_pages to 1 at the start of each loop iteration, like folio_referenced_one() does.  Without this, nr_pages computed by a previous folio_unmap_pte_batch() call can be reused on a later iteration that does not run folio_unmap_pte_batch() again.  mmap a 64K large folio with MAP_ANONYMOUS | MAP_DROPPABLE, then call madvise(MADV_FREE), then make the last page device-exclusive via HMM_DMIRROR_EXCLUSIVE.  Trigger node reclaim through sysfs.  Now, in try_to_unmap_one(), we will first clear the first 15 out of 16 entries mapping the lazyfree folio.  This will set nr_pages to 15.  In the next pvmw walk, this nr_pages gets reused on a device-exclusive pte, thus potentially corrupting folio refcount/mapcount.  At the moment, I have a userspace program which can make the kernel spit out a trace, but the blow up is in folio_referenced_one(), because there are existing bugs in the interaction between device-private and rmap (which too I am investigating).  I did a one liner kernel change to avoid going into folio_referenced_one(), and the kernel blows up at folio_remove_rmap_ptes in try_to_unmap_one which is what I wanted.  Note that the bug is there not since file folio batching but lazyfree folio batching, since device-exclusive only works for anonymous folios.  Userspace visible effect is simply kernel crashing somewhere due to refcount/mapcount corruption.",
  "id": "DEBIAN-CVE-2026-63950",
  "modified": "2026-09-14T16:47:50.511401989Z",
  "published": "2026-07-19T16:17:13.730Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://security-tracker.debian.org/tracker/CVE-2026-63950"
    }
  ],
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "upstream": [
    "CVE-2026-63950"
  ]
}