{"cve":"CVE-2026-63796","nvd":{"published":"2026-07-19T12:16:52.033","modified":"2026-10-19T20:19:20.113","status":"Modified","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nocfs2: reject oversized group bitmap descriptors\n\nocfs2_validate_gd_parent() only bounds bg_bits against the parent\nallocator's chain geometry.  A malicious descriptor can still claim a\nbg_size/bg_bits pair that exceeds the bitmap bytes that physically fit in\nthe group descriptor block, so later bitmap scans and bit updates can run\npast bg_bitmap.\n\nAdd a physical-cap check based on ocfs2_group_bitmap_size() for the parent\nallocator type and reject descriptors whose bg_size or bg_bits exceed that\ncapacity.  Keep the existing chain geometry check so both the on-disk\nbitmap layout and the allocator metadata must agree before the descriptor\nis used.\n\nValidation reproduced this kernel report:\nKASAN use-after-free in _find_next_bit+0x7f/0xc0\nRead of size 8\nCall trace:\n  dump_stack_lvl+0x66/0xa0 (?:?)\n  print_report+0xd0/0x630 (?:?)\n  _find_next_bit+0x7f/0xc0 (?:?)\n  srso_alias_return_thunk+0x5/0xfbef5 (?:?)\n  __virt_addr_valid+0x188/0x2f0 (?:?)\n  kasan_report+0xe4/0x120 (?:?)\n  ocfs2_find_max_contig_free_bits+0x35/0x70 (fs/ocfs2/suballoc.c:1375)\n  ocfs2_block_group_set_bits+0x472/0x4b0 (fs/ocfs2/suballoc.c:1457)\n  ocfs2_cluster_group_search+0x16b/0x440 (fs/ocfs2/suballoc.c:86)\n  ocfs2_bg_discontig_fix_result+0x1ef/0x230 (fs/ocfs2/suballoc.c:1786)\n  ocfs2_search_chain+0x8f8/0x10a0 (fs/ocfs2/suballoc.c:1886)\n  get_page_from_freelist+0x70e/0x2370 (?:?)\n  lock_release+0xc6/0x290 (?:?)\n  do_raw_spin_unlock+0x9a/0x100 (?:?)\n  kasan_unpoison+0x27/0x60 (?:?)\n  __bfs+0x147/0x240 (?:?)\n  get_page_from_freelist+0x83d/0x2370 (?:?)\n  ocfs2_claim_suballoc_bits+0x38c/0xe70 (fs/ocfs2/suballoc.c:96)\n  sched_domains_numa_masks_clear+0x70/0xd0 (?:?)\n  check_irq_usage+0xe8/0xb70 (?:?)\n  __ocfs2_claim_clusters+0x18d/0x4c0 (fs/ocfs2/suballoc.c:2497)\n  check_path+0x24/0x50 (?:?)\n  rcu_is_watching+0x20/0x50 (?:?)\n  check_prev_add+0xfd/0xd00 (?:?)\n  ocfs2_add_clusters_in_btree+0x17d/0x810 (fs/ocfs2/suballoc.c:?)\n  __folio_batch_add_and_move+0x1f5/0x3d0 (?:?)\n  ocfs2_add_inode_data+0xd9/0x120 (fs/ocfs2/suballoc.c:?)\n  filemap_add_folio+0x105/0x1f0 (?:?)\n  ocfs2_write_begin_nolock+0x29f7/0x2f80 (fs/ocfs2/suballoc.c:3043)\n  ocfs2_read_inode_block+0xb5/0x110 (fs/ocfs2/suballoc.c:?)\n  down_write+0xf5/0x180 (?:?)\n  ocfs2_write_begin+0x180/0x240 (fs/ocfs2/suballoc.c:?)\n  __mark_inode_dirty+0x758/0x9a0 (?:?)\n  inode_to_bdi+0x41/0x90 (?:?)\n  balance_dirty_pages_ratelimited_flags+0xf8/0x1d0 (?:?)\n  generic_perform_write+0x252/0x440 (?:?)\n  mnt_put_write_access_file+0x16/0x70 (?:?)\n  file_update_time_flags+0xe4/0x200 (?:?)\n  ocfs2_file_write_iter+0x80a/0x1320 (fs/ocfs2/suballoc.c:?)\n  lock_acquire+0x184/0x2f0 (?:?)\n  ksys_write+0xd2/0x170 (?:?)\n  apparmor_file_permission+0xf5/0x310 (?:?)\n  read_zero+0x8d/0x140 (?:?)\n  lock_is_held_type+0x8f/0x100 (?:?)","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","score":8.8},"cwes":["CWE-125"],"references":["https://git.kernel.org/stable/c/296c6a42b1174395935ca4cfe8f393e37b698d54","https://git.kernel.org/stable/c/336340a0f8a141df8a4eb21a5a86f8ffb87769f6","https://git.kernel.org/stable/c/4cd57ebee395041099fcdfcabb00749ce38d8b27","https://git.kernel.org/stable/c/8f9903b0cdbb3155a8899410330b4b4d583a7a5c","https://git.kernel.org/stable/c/99c21e7263248c3f084756bfae08163cc5d6c62f"],"products":["linux:linux_kernel"],"source":"nvd","synced_at":"2026-10-21T03:43:09.190223697+00:00"},"epss":{"cve":"CVE-2026-63796","score":0.00587,"percentile":0.47782,"date":"2026-10-25"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}