CVE-2026-64567

Status: UPDATED  |  Advisory ID: CVE-2026-64567

Key Details

Affected Products, Subsystems & Sectors

What to Know

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. (NVD)

What to Do

Monitor Linux's web page for any future patch releases.

References