CVE-2026-64567 (GCVE-0-2026-64567)
Vulnerability from cvelistv5
Published
2026-08-05 08:08
Modified
2026-08-19 16:28
Severity ?
VLAI Severity ?
EPSS score ?
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.
References
Impacted products
| Vendor | Product | Version | ||
|---|---|---|---|---|
| Linux | Linux |
Version: 5b0e95bf607ddd59b39f52d3d55e6581c817b530 Version: 5b0e95bf607ddd59b39f52d3d55e6581c817b530 Version: 5b0e95bf607ddd59b39f52d3d55e6581c817b530 Version: 5b0e95bf607ddd59b39f52d3d55e6581c817b530 Version: 5b0e95bf607ddd59b39f52d3d55e6581c817b530 Version: 5b0e95bf607ddd59b39f52d3d55e6581c817b530 Version: 5b0e95bf607ddd59b39f52d3d55e6581c817b530 Version: 5b0e95bf607ddd59b39f52d3d55e6581c817b530 |
||
{
"containers": {
"cna": {
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{
"defaultStatus": "unaffected",
"product": "Linux",
"programFiles": [
"fs/btrfs/free-space-cache.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"versions": [
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],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"versions": [
{
"status": "affected",
"version": "3.2"
},
{
"lessThan": "3.2",
"status": "unaffected",
"version": "0",
"versionType": "semver"
},
{
"lessThanOrEqual": "5.10.*",
"status": "unaffected",
"version": "5.10.265",
"versionType": "semver"
},
{
"lessThanOrEqual": "5.15.*",
"status": "unaffected",
"version": "5.15.216",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.1.*",
"status": "unaffected",
"version": "6.1.183",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.6.*",
"status": "unaffected",
"version": "6.6.148",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.12.*",
"status": "unaffected",
"version": "6.12.101",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.18.*",
"status": "unaffected",
"version": "6.18.42",
"versionType": "semver"
},
{
"lessThanOrEqual": "7.1.*",
"status": "unaffected",
"version": "7.1.6",
"versionType": "semver"
},
{
"lessThanOrEqual": "*",
"status": "unaffected",
"version": "7.2",
"versionType": "original_commit_for_fix"
}
]
}
],
"cpeApplicability": [
{
"nodes": [
{
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"vulnerable": true
},
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}
],
"negate": false,
"operator": "OR"
}
]
}
],
"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"
},
{
"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": {
"engine": "bippy-1.2.0"
}
}
},
"cveMetadata": {
"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"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
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Sightings
| Author | Source | Type | Date |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
- Confirmed: The vulnerability is confirmed from an analyst perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
- Patched: This vulnerability was successfully patched by the user reporting the sighting.
- Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
- Not confirmed: The user expresses doubt about the veracity of the vulnerability.
- Not patched: This vulnerability was not successfully patched by the user reporting the sighting.
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