GHSA-9923-9MC9-HQ5V
Vulnerability from github – Published: 2026-07-19 12:30 – Updated: 2026-07-20 15:31In 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 (?:?)
{
"affected": [],
"aliases": [
"CVE-2026-63796"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-07-19T12:16:52Z",
"severity": "HIGH"
},
"details": "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\u0027s 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 (?:?)",
"id": "GHSA-9923-9mc9-hq5v",
"modified": "2026-07-20T15:31:46Z",
"published": "2026-07-19T12:30:23Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-63796"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/296c6a42b1174395935ca4cfe8f393e37b698d54"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/336340a0f8a141df8a4eb21a5a86f8ffb87769f6"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/4cd57ebee395041099fcdfcabb00749ce38d8b27"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/8f9903b0cdbb3155a8899410330b4b4d583a7a5c"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/99c21e7263248c3f084756bfae08163cc5d6c62f"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/9bd541e09dffff27e5bec0f9f45b0228173a5375"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/c5a125eadba05ba421c4b55e68da22b4a40d32b4"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/d2cd59fa848f9f13796ef214d3b1b5ca9a3fe21e"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
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- Confirmed: The vulnerability has been validated from an analyst's perspective.
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- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.