--- id: CVE-2026-64567 title: |- 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 fr… 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 fr… severity: high cvss: 7.8 cvssVector: 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H' published: '2026-08-05' updated: '2026-08-08' source: NVD sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-64567' references: - url: 'https://git.kernel.org/stable/c/33878ba25e2638bc0c61623d7a05c9ca2b74c039' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/404a0b986e0b6e79738fdf1f0ebbbc43b9acd2a2' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/5e1b2ca6b34939e70fb0785e8222b53cf060016f' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/a2d8d5647ed854e38f941741aea45b9eb15a6350' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/f9fef131fa3f59b857217f522fa5ea430d1b707c' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - 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://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-64567.json - url: 'https://access.redhat.com/security/cve/CVE-2026-64567' - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2511408' - url: 'https://www.cve.org/CVERecord?id=CVE-2026-64567' - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-64567' - url: >- https://lore.kernel.org/linux-cve-announce/2026080558-CVE-2026-64567-a7b8@gregkh/T tags: - nvd - cve.org - csaf - vex - red-hat - score-dispute epss: 0.00125 epssPercentile: 0.02178 ingestedAt: '2026-08-08T20:29:49.170Z' vendor: Linux product: Linux affected: - >- Linux >= 5b0e95bf607ddd59b39f52d3d55e6581c817b530 < 8ded74c654a982dc8581a17b0caa7fcedb20de69 - >- Linux >= 5b0e95bf607ddd59b39f52d3d55e6581c817b530 < c9c38066b6446e83668c041702bb639b0ca49363 - >- Linux >= 5b0e95bf607ddd59b39f52d3d55e6581c817b530 < 094734c7aaa2b36751dc32480a680a4952685e78 - >- Linux >= 5b0e95bf607ddd59b39f52d3d55e6581c817b530 < 33878ba25e2638bc0c61623d7a05c9ca2b74c039 - >- Linux >= 5b0e95bf607ddd59b39f52d3d55e6581c817b530 < 404a0b986e0b6e79738fdf1f0ebbbc43b9acd2a2 - >- Linux >= 5b0e95bf607ddd59b39f52d3d55e6581c817b530 < 5e1b2ca6b34939e70fb0785e8222b53cf060016f - >- Linux >= 5b0e95bf607ddd59b39f52d3d55e6581c817b530 < f9fef131fa3f59b857217f522fa5ea430d1b707c - >- Linux >= 5b0e95bf607ddd59b39f52d3d55e6581c817b530 < a2d8d5647ed854e38f941741aea45b9eb15a6350 - Linux 3.2 ssvc: exploitation: none automatable: 'no' technicalImpact: total timestamp: '2026-10-16T15:42:59.944567Z' cwe: - CWE-125 scores: nvd: 7.8 vendor: 5.5 cna: 7.8 --- ## Overview 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 = 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. ## Remediation Refer to the linked advisories for vendor-supplied fixes and affected version ranges. ## Vendor advisories - **Red Hat VEX** · Moderate · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7 · no fix planned: Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 7 · updated 2026-10-16 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-64567.json)