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CVE-2026-64567 (GCVE-0-2026-64567)

Vulnerability from cvelistv5 – Published: 2026-08-05 08:08 – Updated: 2026-08-19 16:28
VLAI
Title
btrfs: reject free space cache with more entries than pages
Summary
In the Linux kernel, the following vulnerability has been resolved: btrfs: reject free space cache with more entries than pages When loading a v1 free space cache, __load_free_space_cache() takes num_entries and num_bitmaps straight from the on-disk btrfs_free_space_header. That header is stored in the tree_root under a key with type 0, which the tree-checker has no case for, so neither count is validated before the load trusts it. The load loops num_entries times and maps the next page whenever the current one runs out, going through io_ctl_check_crc() -> io_ctl_map_page(), which does io_ctl->pages[io_ctl->index++]. But pages[] is allocated in io_ctl_init() from the cache inode's i_size, not from num_entries: num_pages = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE); io_ctl->pages = kcalloc(num_pages, sizeof(struct page *), GFP_NOFS); So if num_entries claims more records than the pages can hold, io_ctl->index runs off the end of pages[]. The write side never hits this because io_ctl_add_entry() and io_ctl_add_bitmap() both stop once io_ctl->index >= io_ctl->num_pages; the read side just never had the same check. To trigger it, take a clean cache (num_entries = <N> here), set num_entries in the header to 0x10000, and fix up the leaf checksum so it still passes the tree-checker. The cache inode has i_size = 65536, so num_pages is 16 and pages[] is a 16-pointer (kmalloc-128) array. The load now tries to read 65536 entries, io_ctl->index walks up to 16, and pages[16] is read past the array: BUG: KASAN: slab-out-of-bounds in io_ctl_check_crc (fs/btrfs/free-space-cache.c:420 fs/btrfs/free-space-cache.c:565) Read of size 8 at addr ffff88800c833a80 by task kworker/u8:3/58 io_ctl_check_crc (fs/btrfs/free-space-cache.c:420 fs/btrfs/free-space-cache.c:565) __load_free_space_cache (fs/btrfs/free-space-cache.c:655 fs/btrfs/free-space-cache.c:820) load_free_space_cache (fs/btrfs/free-space-cache.c:1017) caching_thread (fs/btrfs/block-group.c:880) btrfs_work_helper (fs/btrfs/async-thread.c:312) process_one_work worker_thread kthread ret_from_fork free-space-cache.c:420 is io_ctl_map_page(), inlined into io_ctl_check_crc() at line 565, which is why that is the frame KASAN names. The out-of-bounds slot is then treated as a struct page and handed to crc32c(), so the bad read turns into a GP fault. Add the missing check to io_ctl_check_crc(), which is where both the entry loop and the bitmap loop end up. When num_entries is too large the load now fails like any corrupt cache: __load_free_space_cache() drops it and rebuilds the free space from the extent tree, so a valid cache is never rejected.
Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 5b0e95bf607ddd59b39f52d3d55e6581c817b530 , < 8ded74c654a982dc8581a17b0caa7fcedb20de69 (git)
Affected: 5b0e95bf607ddd59b39f52d3d55e6581c817b530 , < c9c38066b6446e83668c041702bb639b0ca49363 (git)
Affected: 5b0e95bf607ddd59b39f52d3d55e6581c817b530 , < 094734c7aaa2b36751dc32480a680a4952685e78 (git)
Affected: 5b0e95bf607ddd59b39f52d3d55e6581c817b530 , < 33878ba25e2638bc0c61623d7a05c9ca2b74c039 (git)
Affected: 5b0e95bf607ddd59b39f52d3d55e6581c817b530 , < 404a0b986e0b6e79738fdf1f0ebbbc43b9acd2a2 (git)
Affected: 5b0e95bf607ddd59b39f52d3d55e6581c817b530 , < 5e1b2ca6b34939e70fb0785e8222b53cf060016f (git)
Affected: 5b0e95bf607ddd59b39f52d3d55e6581c817b530 , < f9fef131fa3f59b857217f522fa5ea430d1b707c (git)
Affected: 5b0e95bf607ddd59b39f52d3d55e6581c817b530 , < a2d8d5647ed854e38f941741aea45b9eb15a6350 (git)
guessed Create a notification for this product.
Linux Linux Affected: 3.2
Unaffected: 0 , < 3.2 (semver)
Unaffected: 5.10.265 , ≤ 5.10.* (semver)
Unaffected: 5.15.216 , ≤ 5.15.* (semver)
Unaffected: 6.1.183 , ≤ 6.1.* (semver)
Unaffected: 6.6.148 , ≤ 6.6.* (semver)
Unaffected: 6.12.101 , ≤ 6.12.* (semver)
Unaffected: 6.18.42 , ≤ 6.18.* (semver)
Unaffected: 7.1.6 , ≤ 7.1.* (semver)
Unaffected: 7.2 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbtrfs: reject free space cache with more entries than pages\n\nWhen loading a v1 free space cache, __load_free_space_cache() takes\nnum_entries and num_bitmaps straight from the on-disk\nbtrfs_free_space_header. That header is stored in the tree_root under a key\nwith type 0, which the tree-checker has no case for, so neither count is\nvalidated before the load trusts it.\n\nThe load loops num_entries times and maps the next page whenever the current\none runs out, going through io_ctl_check_crc() -\u003e io_ctl_map_page(), which\ndoes io_ctl-\u003epages[io_ctl-\u003eindex++]. But pages[] is allocated in\nio_ctl_init() from the cache inode\u0027s i_size, not from num_entries:\n\n\tnum_pages = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);\n\tio_ctl-\u003epages = kcalloc(num_pages, sizeof(struct page *), GFP_NOFS);\n\nSo if num_entries claims more records than the pages can hold, io_ctl-\u003eindex\nruns off the end of pages[]. The write side never hits this because\nio_ctl_add_entry() and io_ctl_add_bitmap() both stop once\nio_ctl-\u003eindex \u003e= io_ctl-\u003enum_pages; the read side just never had the same\ncheck.\n\nTo trigger it, take a clean cache (num_entries = \u003cN\u003e here), set num_entries\nin the header to 0x10000, and fix up the leaf checksum so it still passes\nthe tree-checker. The cache inode has i_size = 65536, so num_pages is 16 and\npages[] is a 16-pointer (kmalloc-128) array. The load now tries to read\n65536 entries, io_ctl-\u003eindex walks up to 16, and pages[16] is read past the\narray:\n\n  BUG: KASAN: slab-out-of-bounds in io_ctl_check_crc (fs/btrfs/free-space-cache.c:420 fs/btrfs/free-space-cache.c:565)\n  Read of size 8 at addr ffff88800c833a80 by task kworker/u8:3/58\n   io_ctl_check_crc (fs/btrfs/free-space-cache.c:420 fs/btrfs/free-space-cache.c:565)\n   __load_free_space_cache (fs/btrfs/free-space-cache.c:655 fs/btrfs/free-space-cache.c:820)\n   load_free_space_cache (fs/btrfs/free-space-cache.c:1017)\n   caching_thread (fs/btrfs/block-group.c:880)\n   btrfs_work_helper (fs/btrfs/async-thread.c:312)\n   process_one_work\n   worker_thread\n   kthread\n   ret_from_fork\n\nfree-space-cache.c:420 is io_ctl_map_page(), inlined into io_ctl_check_crc()\nat line 565, which is why that is the frame KASAN names. The out-of-bounds\nslot is then treated as a struct page and handed to crc32c(), so the bad\nread turns into a GP fault.\n\nAdd the missing check to io_ctl_check_crc(), which is where both the entry\nloop and the bitmap loop end up. When num_entries is too large the load now\nfails like any corrupt cache: __load_free_space_cache() drops it and rebuilds\nthe free space from the extent tree, so a valid cache is never rejected."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - The bug is reached only by mounting a crafted btrfs image so caching_thread \u2192 load_free_space_cache \u2192 __load_free_space_cache runs; there is no network or adjacent protocol path into v1 free-space cache loading.\nAC:L - The attacker authors a v1 cache with inflated num_entries (and a matching leaf checksum); cache_generation auto-enables SPACE_CACHE on mount, and the OOB in io_ctl_check_crc/io_ctl_map_page is deterministic with no race or uncontrolled condition.\nPR:L - btrfs lacks FS_USERNS_MOUNT, but an unprivileged local user can loop-setup and mount a crafted image via udisks2/polkit on typical desktops/kiosks; real init-namespace root is not required.\nUI:N - In the loop/udisks mount scenario the attacker mounts the image themselves; no separate victim must open a file, click through a prompt, or otherwise interact.\nS:U - The slab OOB and resulting kernel memory misuse stay inside the host kernel\u0027s authority; no VM escape, IOMMU bypass, or sandbox boundary is crossed.\nC:H - An out-of-bounds pages[] read yields a forged struct page pointer that is passed to page_address/crc32c and then used as the source for further cache parsing, giving an arbitrary kernel-memory read primitive once adjacent slab contents are groomed.\nI:H - The forged page pointer continues into entry/bitmap load paths (including copy_page into kernel bitmaps and linking attacker-controlled free-space records), a memory-corruption primitive exploitable for arbitrary write and control-flow hijack.\nA:H - Without a valid page pointer the OOB dereference reliably faults (KASAN slab-OOB then GP fault on crc32c as in the report), crashing or oopsing the kernel."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-19T16:28:41.793Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/8ded74c654a982dc8581a17b0caa7fcedb20de69"
        },
        {
          "url": "https://git.kernel.org/stable/c/c9c38066b6446e83668c041702bb639b0ca49363"
        },
        {
          "url": "https://git.kernel.org/stable/c/094734c7aaa2b36751dc32480a680a4952685e78"
        },
        {
          "url": "https://git.kernel.org/stable/c/33878ba25e2638bc0c61623d7a05c9ca2b74c039"
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          "url": "https://git.kernel.org/stable/c/404a0b986e0b6e79738fdf1f0ebbbc43b9acd2a2"
        },
        {
          "url": "https://git.kernel.org/stable/c/5e1b2ca6b34939e70fb0785e8222b53cf060016f"
        },
        {
          "url": "https://git.kernel.org/stable/c/f9fef131fa3f59b857217f522fa5ea430d1b707c"
        },
        {
          "url": "https://git.kernel.org/stable/c/a2d8d5647ed854e38f941741aea45b9eb15a6350"
        }
      ],
      "title": "btrfs: reject free space cache with more entries than pages",
      "x_generator": {
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    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-64567",
    "datePublished": "2026-08-05T08:08:06.015Z",
    "dateReserved": "2026-07-19T15:36:31.797Z",
    "dateUpdated": "2026-08-19T16:28:41.793Z",
    "state": "PUBLISHED"
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      "cve": "CVE-2026-64567",
      "date": "2026-09-20",
      "epss": "0.0012",
      "percentile": "0.02125"
    },
    "microsoft_vex": {
      "current_release_date": "2026-08-09T01:43:07.000Z",
      "cve": "CVE-2026-64567",
      "id": "msrc_CVE-2026-64567",
      "initial_release_date": "2026-08-09T01:43:07.000Z",
      "product_status:fixed": "1",
      "product_status:known_affected": "1",
      "source": "Microsoft CSAF VEX",
      "status": "final",
      "title": "btrfs: reject free space cache with more entries than pages",
      "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-64567.json",
      "version": "1"
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                    "versionType": "original_commit_for_fix"
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            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
          }
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        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbtrfs: reject free space cache with more entries than pages\n\nWhen loading a v1 free space cache, __load_free_space_cache() takes\nnum_entries and num_bitmaps straight from the on-disk\nbtrfs_free_space_header. That header is stored in the tree_root under a key\nwith type 0, which the tree-checker has no case for, so neither count is\nvalidated before the load trusts it.\n\nThe load loops num_entries times and maps the next page whenever the current\none runs out, going through io_ctl_check_crc() -\u003e io_ctl_map_page(), which\ndoes io_ctl-\u003epages[io_ctl-\u003eindex++]. But pages[] is allocated in\nio_ctl_init() from the cache inode\u0027s i_size, not from num_entries:\n\n\tnum_pages = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);\n\tio_ctl-\u003epages = kcalloc(num_pages, sizeof(struct page *), GFP_NOFS);\n\nSo if num_entries claims more records than the pages can hold, io_ctl-\u003eindex\nruns off the end of pages[]. The write side never hits this because\nio_ctl_add_entry() and io_ctl_add_bitmap() both stop once\nio_ctl-\u003eindex \u003e= io_ctl-\u003enum_pages; the read side just never had the same\ncheck.\n\nTo trigger it, take a clean cache (num_entries = \u003cN\u003e here), set num_entries\nin the header to 0x10000, and fix up the leaf checksum so it still passes\nthe tree-checker. The cache inode has i_size = 65536, so num_pages is 16 and\npages[] is a 16-pointer (kmalloc-128) array. The load now tries to read\n65536 entries, io_ctl-\u003eindex walks up to 16, and pages[16] is read past the\narray:\n\n  BUG: KASAN: slab-out-of-bounds in io_ctl_check_crc (fs/btrfs/free-space-cache.c:420 fs/btrfs/free-space-cache.c:565)\n  Read of size 8 at addr ffff88800c833a80 by task kworker/u8:3/58\n   io_ctl_check_crc (fs/btrfs/free-space-cache.c:420 fs/btrfs/free-space-cache.c:565)\n   __load_free_space_cache (fs/btrfs/free-space-cache.c:655 fs/btrfs/free-space-cache.c:820)\n   load_free_space_cache (fs/btrfs/free-space-cache.c:1017)\n   caching_thread (fs/btrfs/block-group.c:880)\n   btrfs_work_helper (fs/btrfs/async-thread.c:312)\n   process_one_work\n   worker_thread\n   kthread\n   ret_from_fork\n\nfree-space-cache.c:420 is io_ctl_map_page(), inlined into io_ctl_check_crc()\nat line 565, which is why that is the frame KASAN names. The out-of-bounds\nslot is then treated as a struct page and handed to crc32c(), so the bad\nread turns into a GP fault.\n\nAdd the missing check to io_ctl_check_crc(), which is where both the entry\nloop and the bitmap loop end up. When num_entries is too large the load now\nfails like any corrupt cache: __load_free_space_cache() drops it and rebuilds\nthe free space from the extent tree, so a valid cache is never rejected."
          }
        ],
        "id": "CVE-2026-64567",
        "lastModified": "2026-08-19T17:20:16.587",
        "metrics": {
          "cvssMetricV31": [
            {
              "cvssData": {
                "attackComplexity": "LOW",
                "attackVector": "LOCAL",
                "availabilityImpact": "HIGH",
                "baseScore": 7.8,
                "baseSeverity": "HIGH",
                "confidentialityImpact": "HIGH",
                "integrityImpact": "HIGH",
                "privilegesRequired": "LOW",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
                "version": "3.1"
              },
              "exploitabilityScore": 1.8,
              "impactScore": 5.9,
              "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
              "type": "Secondary"
            }
          ]
        },
        "published": "2026-08-05T08:16:36.277",
        "references": [
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/094734c7aaa2b36751dc32480a680a4952685e78"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/33878ba25e2638bc0c61623d7a05c9ca2b74c039"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/404a0b986e0b6e79738fdf1f0ebbbc43b9acd2a2"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/5e1b2ca6b34939e70fb0785e8222b53cf060016f"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/8ded74c654a982dc8581a17b0caa7fcedb20de69"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/a2d8d5647ed854e38f941741aea45b9eb15a6350"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/c9c38066b6446e83668c041702bb639b0ca49363"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/f9fef131fa3f59b857217f522fa5ea430d1b707c"
          }
        ],
        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Received"
      }
    },
    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-08-08T16:35:09+00:00",
      "cve": "CVE-2026-64567",
      "id": "CVE-2026-64567",
      "initial_release_date": "2026-08-05T00:00:00+00:00",
      "product_status:known_affected": "118",
      "product_status:known_not_affected": "156",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: btrfs: reject free space cache with more entries than pages",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-64567.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "moderate",
      "current_release_date": "2026-09-18T00:38:00Z",
      "cve": "CVE-2026-64567",
      "id": "CVE-2026-64567",
      "initial_release_date": "2026-08-06T01:06:32Z",
      "product_status:first_fixed": "23",
      "product_status:known_affected": "731",
      "product_status:recommended": "111",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-64567",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-64567.json",
      "version": "11"
    }
  }
}



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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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  • 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.
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  • 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.


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Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.