CVE-2026-63796

Status: UPDATED  |  Advisory ID: CVE-2026-63796

Key Details

Affected Products, Subsystems & Sectors

What to Know

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 (?:?) (NVD)

What to Do

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

References