{"id":"CVE-2026-64567","summary":"btrfs: reject free space cache with more entries than pages","details":"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's 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.","modified":"2026-08-06T03:48:34.414937612Z","published":"2026-08-05T08:08:06.015Z","database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/64xxx/CVE-2026-64567.json"},"references":[{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"},{"type":"WEB","url":"https://git.kernel.org/stable/c/33878ba25e2638bc0c61623d7a05c9ca2b74c039"},{"type":"WEB","url":"https://git.kernel.org/stable/c/404a0b986e0b6e79738fdf1f0ebbbc43b9acd2a2"},{"type":"WEB","url":"https://git.kernel.org/stable/c/5e1b2ca6b34939e70fb0785e8222b53cf060016f"},{"type":"WEB","url":"https://git.kernel.org/stable/c/a2d8d5647ed854e38f941741aea45b9eb15a6350"},{"type":"WEB","url":"https://git.kernel.org/stable/c/f9fef131fa3f59b857217f522fa5ea430d1b707c"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/64xxx/CVE-2026-64567.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-64567"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"5b0e95bf607ddd59b39f52d3d55e6581c817b530"},{"fixed":"33878ba25e2638bc0c61623d7a05c9ca2b74c039"},{"fixed":"404a0b986e0b6e79738fdf1f0ebbbc43b9acd2a2"},{"fixed":"5e1b2ca6b34939e70fb0785e8222b53cf060016f"},{"fixed":"f9fef131fa3f59b857217f522fa5ea430d1b707c"},{"fixed":"a2d8d5647ed854e38f941741aea45b9eb15a6350"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-64567.json"}},{"package":{"name":"Kernel","ecosystem":"Linux"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"3.2.0"},{"fixed":"6.6.148"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.7.0"},{"fixed":"6.12.101"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.13.0"},{"fixed":"6.18.42"}]},{"type":"ECOSYSTEM","events":[{"introduced":"6.19.0"},{"fixed":"7.1.6"}]}],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-64567.json"}}],"schema_version":"1.8.0"}