{
  "cveId": "CVE-2025-39879",
  "url": "https://patchblox.com/security/cve/CVE-2025-39879",
  "summary": "CVE-2025-39879 is fixed in linux on 1 platform by DEBIAN-CVE-2025-39879 (version 6.16.8-1), released September 23, 2025. It is not reported as exploited. Patch Radar priority: Routine.",
  "title": "linux: In the Linux kernel, the following vulnerability has been resolved:  ceph: always call ceph_shift_unused_folios_left(...",
  "description": "In the Linux kernel, the following vulnerability has been resolved:  ceph: always call ceph_shift_unused_folios_left()  The function ceph_process_folio_batch() sets folio_batch entries to NULL, which is an illegal state.  Before folio_batch_release() crashes due to this API violation, the function ceph_shift_unused_folios_left() is supposed to remove those NULLs from the array.  However, since commit ce80b76dd327 (\u0022ceph: introduce ceph_process_folio_batch() method\u0022), this shifting doesn\u0027t happen anymore because the \u0022for\u0022 loop got moved to ceph_process_folio_batch(), and now the \u0060i\u0060 variable that remains in ceph_writepages_start() doesn\u0027t get incremented anymore, making the shifting effectively unreachable much of the time.  Later, commit 1551ec61dc55 (\u0022ceph: introduce ceph_submit_write() method\u0022) added more preconditions for doing the shift, replacing the \u0060i\u0060 check (with something that is still just as broken):  - if ceph_process_folio_batch() fails, shifting never happens  - if ceph_move_dirty_page_in_page_array() was never called (because   ceph_process_folio_batch() has returned early for some of various   reasons), shifting never happens  - if \u0060processed_in_fbatch\u0060 is zero (because ceph_process_folio_batch()   has returned early for some of the reasons mentioned above or   because ceph_move_dirty_page_in_page_array() has failed), shifting   never happens  Since those two commits, any problem in ceph_process_folio_batch() could crash the kernel, e.g. this way:   BUG: kernel NULL pointer dereference, address: 0000000000000034  #PF: supervisor write access in kernel mode  #PF: error_code(0x0002) - not-present page  PGD 0 P4D 0  Oops: Oops: 0002 [#1] SMP NOPTI  CPU: 172 UID: 0 PID: 2342707 Comm: kworker/u778:8 Not tainted 6.15.10-cm4all1-es #714 NONE  Hardware name: Dell Inc. PowerEdge R7615/0G9DHV, BIOS 1.6.10 12/08/2023  Workqueue: writeback wb_workfn (flush-ceph-1)  RIP: 0010:folios_put_refs\u002B0x85/0x140  Code: 83 c5 01 39 e8 7e 76 48 63 c5 49 8b 5c c4 08 b8 01 00 00 00 4d 85 ed 74 05 41 8b 44 ad 00 48 8b 15 b0 \u003E  RSP: 0018:ffffb880af8db778 EFLAGS: 00010207  RAX: 0000000000000001 RBX: 0000000000000000 RCX: 0000000000000003  RDX: ffffe377cc3b0000 RSI: 0000000000000000 RDI: ffffb880af8db8c0  RBP: 0000000000000000 R08: 000000000000007d R09: 000000000102b86f  R10: 0000000000000001 R11: 00000000000000ac R12: ffffb880af8db8c0  R13: 0000000000000000 R14: 0000000000000000 R15: ffff9bd262c97000  FS:  0000000000000000(0000) GS:ffff9c8efc303000(0000) knlGS:0000000000000000  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033  CR2: 0000000000000034 CR3: 0000000160958004 CR4: 0000000000770ef0  PKRU: 55555554  Call Trace:   \u003CTASK\u003E   ceph_writepages_start\u002B0xeb9/0x1410  The crash can be reproduced easily by changing the ceph_check_page_before_write() return value to \u0060-E2BIG\u0060.  (Interestingly, the crash happens only if \u0060huge_zero_folio\u0060 has already been allocated; without \u0060huge_zero_folio\u0060, is_huge_zero_folio(NULL) returns true and folios_put_refs() skips NULL entries instead of dereferencing them.  That makes reproducing the bug somewhat unreliable.  See https://lore.kernel.org/20250826231626.218675-1-max.kellermann@ionos.com for a discussion of this detail.)  My suggestion is to move the ceph_shift_unused_folios_left() to right after ceph_process_folio_batch() to ensure it always gets called to fix up the illegal folio_batch state.",
  "published": "2025-09-23T06:15:47Z",
  "severity": "medium",
  "cvss": 5.5,
  "cvssVector": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
  "epss": 0.00187,
  "epssPercentile": 0.08374,
  "priority": "Routine",
  "priorityTier": 4,
  "exploited": false,
  "vendorExploited": false,
  "disclosed": false,
  "fixes": [
    {
      "platform": "linux",
      "product": "linux",
      "release": "Debian 14",
      "fixedVersion": "6.16.8-1",
      "fix": "DEBIAN-CVE-2025-39879",
      "url": "https://patchblox.com/security/fix/linux/debian-cve-2025-39879",
      "released": "2025-09-23T06:15:47Z"
    }
  ],
  "noFixYet": [],
  "dataAsOf": "2026-11-08T13:06:02Z",
  "attribution": {
    "text": "Data: Patchblox Patch Radar",
    "url": "https://patchblox.com/security/patch-radar",
    "terms": "https://patchblox.com/security/patch-radar/use-the-data"
  }
}