CVE-2025-39879 (GCVE-0-2025-39879)

Vulnerability from cvelistv5 – Published: 2025-09-23 06:00 – Updated: 2026-05-11 21:38
VLAI
Title
ceph: always call ceph_shift_unused_folios_left()
Summary
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 ("ceph: introduce ceph_process_folio_batch() method"), this shifting doesn't happen anymore because the "for" loop got moved to ceph_process_folio_batch(), and now the `i` variable that remains in ceph_writepages_start() doesn't get incremented anymore, making the shifting effectively unreachable much of the time. Later, commit 1551ec61dc55 ("ceph: introduce ceph_submit_write() method") added more preconditions for doing the shift, replacing the `i` 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 `processed_in_fbatch` 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+0x85/0x140 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 > 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: <TASK> ceph_writepages_start+0xeb9/0x1410 The crash can be reproduced easily by changing the ceph_check_page_before_write() return value to `-E2BIG`. (Interestingly, the crash happens only if `huge_zero_folio` has already been allocated; without `huge_zero_folio`, 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.
Severity
5.5 (Medium)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
CWE
  • CWE-476 - NULL Pointer Dereference
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: ce80b76dd32764cc914975777e058d4fae4f0ea0 , < 289b6615cf553d98509a9b273195d9936da1cfb2 (git)
Affected: ce80b76dd32764cc914975777e058d4fae4f0ea0 , < cce7c15faaac79b532a07ed6ab8332280ad83762 (git)
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Linux Linux Affected: 6.15
Unaffected: 0 , < 6.15 (semver)
Unaffected: 6.16.8 , ≤ 6.16.* (semver)
Unaffected: 6.17 , ≤ * (original_commit_for_fix)
Create a notification for this product.
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    "vulnrichment": {
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Before folio_batch_release() crashes\\ndue to this API violation, the function ceph_shift_unused_folios_left()\\nis supposed to remove those NULLs from the array.\\n\\nHowever, since commit ce80b76dd327 (\\\"ceph: introduce\\nceph_process_folio_batch() method\\\"), this shifting doesn\u0027t happen\\nanymore because the \\\"for\\\" loop got moved to ceph_process_folio_batch(),\\nand now the `i` variable that remains in ceph_writepages_start()\\ndoesn\u0027t get incremented anymore, making the shifting effectively\\nunreachable much of the time.\\n\\nLater, commit 1551ec61dc55 (\\\"ceph: introduce ceph_submit_write()\\nmethod\\\") added more preconditions for doing the shift, replacing the\\n`i` check (with something that is still just as broken):\\n\\n- if ceph_process_folio_batch() fails, shifting never happens\\n\\n- if ceph_move_dirty_page_in_page_array() was never called (because\\n  ceph_process_folio_batch() has returned early for some of various\\n  reasons), shifting never happens\\n\\n- if `processed_in_fbatch` is zero (because ceph_process_folio_batch()\\n  has returned early for some of the reasons mentioned above or\\n  because ceph_move_dirty_page_in_page_array() has failed), shifting\\n  never happens\\n\\nSince those two commits, any problem in ceph_process_folio_batch()\\ncould crash the kernel, e.g. this way:\\n\\n BUG: kernel NULL pointer dereference, address: 0000000000000034\\n #PF: supervisor write access in kernel mode\\n #PF: error_code(0x0002) - not-present page\\n PGD 0 P4D 0\\n Oops: Oops: 0002 [#1] SMP NOPTI\\n CPU: 172 UID: 0 PID: 2342707 Comm: kworker/u778:8 Not tainted 6.15.10-cm4all1-es #714 NONE\\n Hardware name: Dell Inc. PowerEdge R7615/0G9DHV, BIOS 1.6.10 12/08/2023\\n Workqueue: writeback wb_workfn (flush-ceph-1)\\n RIP: 0010:folios_put_refs+0x85/0x140\\n 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\\n RSP: 0018:ffffb880af8db778 EFLAGS: 00010207\\n RAX: 0000000000000001 RBX: 0000000000000000 RCX: 0000000000000003\\n RDX: ffffe377cc3b0000 RSI: 0000000000000000 RDI: ffffb880af8db8c0\\n RBP: 0000000000000000 R08: 000000000000007d R09: 000000000102b86f\\n R10: 0000000000000001 R11: 00000000000000ac R12: ffffb880af8db8c0\\n R13: 0000000000000000 R14: 0000000000000000 R15: ffff9bd262c97000\\n FS:  0000000000000000(0000) GS:ffff9c8efc303000(0000) knlGS:0000000000000000\\n CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033\\n CR2: 0000000000000034 CR3: 0000000160958004 CR4: 0000000000770ef0\\n PKRU: 55555554\\n Call Trace:\\n  \u003cTASK\u003e\\n  ceph_writepages_start+0xeb9/0x1410\\n\\nThe crash can be reproduced easily by changing the\\nceph_check_page_before_write() return value to `-E2BIG`.\\n\\n(Interestingly, the crash happens only if `huge_zero_folio` has\\nalready been allocated; without `huge_zero_folio`,\\nis_huge_zero_folio(NULL) returns true and folios_put_refs() skips NULL\\nentries instead of dereferencing them.  That makes reproducing the bug\\nsomewhat unreliable.  See\\nhttps://lore.kernel.org/20250826231626.218675-1-max.kellermann@ionos.com\\nfor a discussion of this detail.)\\n\\nMy suggestion is to move the ceph_shift_unused_folios_left() to right\\nafter ceph_process_folio_batch() to ensure it always gets called to\\nfix up the illegal folio_batch state.\"}], \"cpeApplicability\": [{\"nodes\": [{\"negate\": false, \"cpeMatch\": [{\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.16.8\", \"versionStartIncluding\": \"6.15\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.17\", \"versionStartIncluding\": \"6.15\"}], \"operator\": \"OR\"}]}], \"providerMetadata\": {\"orgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"shortName\": \"Linux\", \"dateUpdated\": \"2025-09-29T06:01:38.349Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2025-39879\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-01-14T19:33:12.440Z\", \"dateReserved\": \"2025-04-16T07:20:57.144Z\", \"assignerOrgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"datePublished\": \"2025-09-23T06:00:49.377Z\", \"assignerShortName\": \"Linux\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}


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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

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Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



Detection rules are retrieved from Rulezet.