{"id":"DEBIAN-CVE-2026-63796","details":"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 (?:?)","modified":"2026-09-29T13:04:13.604730435Z","published":"2026-07-19T12:16:52.033Z","upstream":["CVE-2026-63796"],"references":[{"type":"ADVISORY","url":"https://security-tracker.debian.org/tracker/CVE-2026-63796"}],"affected":[{"package":{"name":"linux","ecosystem":"Debian:12","purl":"pkg:deb/debian/linux?arch=source&distro=bookworm"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.1.177-1"}]}],"versions":["6.1.106-1","6.1.106-2","6.1.106-3","6.1.112-1","6.1.115-1","6.1.119-1","6.1.123-1","6.1.124-1","6.1.128-1","6.1.129-1","6.1.133-1","6.1.135-1","6.1.137-1","6.1.139-1","6.1.140-1","6.1.147-1","6.1.148-1","6.1.153-1","6.1.158-1","6.1.159-1","6.1.162-1","6.1.164-1","6.1.170-1","6.1.170-2","6.1.170-3","6.1.172-1","6.1.174-1","6.1.176-1","6.1.27-1","6.1.37-1","6.1.38-1","6.1.38-2","6.1.38-2~bpo11+1","6.1.38-3","6.1.38-4","6.1.38-4~bpo11+1","6.1.52-1","6.1.55-1","6.1.55-1~bpo11+1","6.1.64-1","6.1.66-1","6.1.67-1","6.1.69-1","6.1.69-1~bpo11+1","6.1.76-1","6.1.76-1~bpo11+1","6.1.82-1","6.1.85-1","6.1.90-1","6.1.90-1~bpo11+1","6.1.94-1","6.1.94-1~bpo11+1","6.1.98-1","6.1.99-1"],"ecosystem_specific":{"urgency":"not yet assigned"},"database_specific":{"source":"https://storage.googleapis.com/osv-test-debian-osv/debian-cve-osv/DEBIAN-CVE-2026-63796.json"}},{"package":{"name":"linux","ecosystem":"Debian:13","purl":"pkg:deb/debian/linux?arch=source&distro=trixie"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.12.95-1"}]}],"versions":["6.12.38-1","6.12.41-1","6.12.43-1","6.12.43-1~bpo12+1","6.12.48-1","6.12.57-1","6.12.57-1~bpo12+1","6.12.63-1","6.12.63-1~bpo12+1","6.12.69-1","6.12.69-1~bpo12+1","6.12.73-1","6.12.73-1~bpo12+1","6.12.74-1","6.12.74-2","6.12.74-2~bpo12+1","6.12.85-1","6.12.85-1~bpo12+1","6.12.86-1","6.12.86-1~bpo12+1","6.12.88-1","6.12.88-1~bpo12+1","6.12.90-1","6.12.90-1~bpo12+1","6.12.90-2","6.12.90-2~bpo12+1","6.12.94-1","6.12.94-1~bpo12+1","6.12.95-1~bpo12+1"],"ecosystem_specific":{"urgency":"not yet 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