btrfs: reject free space cache with more entries than pages

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-64567
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-05 08:16:36 UTC
Updated2026-08-08 15:16:31 UTC
DescriptionIn 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.

Risk And Classification

Primary CVSS: v3.1 7.8 HIGH from 416baaa9-dc9f-4396-8d5f-8c081fb06d67

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

EPSS: 0.001560000 probability, percentile 0.052580000 (date 2026-08-07)

VersionSourceTypeScoreSeverityVector
3.1416baaa9-dc9f-4396-8d5f-8c081fb06d67Secondary7.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
3.1CNADECLARED7.8HIGHCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 5b0e95bf607ddd59b39f52d3d55e6581c817b530 33878ba25e2638bc0c61623d7a05c9ca2b74c039 git Not specified
CNA Linux Linux affected 5b0e95bf607ddd59b39f52d3d55e6581c817b530 404a0b986e0b6e79738fdf1f0ebbbc43b9acd2a2 git Not specified
CNA Linux Linux affected 5b0e95bf607ddd59b39f52d3d55e6581c817b530 5e1b2ca6b34939e70fb0785e8222b53cf060016f git Not specified
CNA Linux Linux affected 5b0e95bf607ddd59b39f52d3d55e6581c817b530 f9fef131fa3f59b857217f522fa5ea430d1b707c git Not specified
CNA Linux Linux affected 5b0e95bf607ddd59b39f52d3d55e6581c817b530 a2d8d5647ed854e38f941741aea45b9eb15a6350 git Not specified
CNA Linux Linux affected 3.2 Not specified
CNA Linux Linux unaffected 3.2 semver Not specified
CNA Linux Linux unaffected 6.6.148 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.101 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.42 6.18.* semver Not specified
CNA Linux Linux unaffected 7.1.6 7.1.* semver Not specified
CNA Linux Linux unaffected 7.2-rc4 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/a2d8d5647ed854e38f941741aea45b9eb15a6350 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/33878ba25e2638bc0c61623d7a05c9ca2b74c039 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/5e1b2ca6b34939e70fb0785e8222b53cf060016f 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/404a0b986e0b6e79738fdf1f0ebbbc43b9acd2a2 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/f9fef131fa3f59b857217f522fa5ea430d1b707c 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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