hfs: port HFS+ b-tree bitmap corruption check

Browse source

In HFS+ filesystems, during b-tree open (hfs_btree_open()), the code
verifies that the allocation map bit for the tree header (node 0) is
set. If not, it indicates a corrupted map record/bitmap and mounts
the volume as read-only (SB_RDONLY) to prevent further damage.

HFS filesystems share the same b-tree structure but currently lack
this corruption detection check.

Port this check to HFS, aligning its implementation with HFS+ to
maintain consistent b-tree logic across both filesystems:
1. Define struct hfs_bmap_ctx, and define HFS_TREE_HEAD and the relevant
   map record indices in include/linux/hfs_common.h.
2. Port the necessary offset and length validation helpers to
   fs/hfs/btree.h as static inline functions with robust null pointer
   checks.
3. Implement static hfs_bmap_get_map_page() in fs/hfs/btree.c.
4. Implement static hfs_bmap_test_bit() in fs/hfs/btree.c to inspect
   the B-tree bitmap using the get_map_page helper.
5. Implement static hfs_bmap_clear_bit() in fs/hfs/btree.c.
6. Rewrite hfs_bmap_alloc() in fs/hfs/btree.c to use the unified
   hfs_bmap_get_map_page() helper, eliminating redundant page and offset
   calculation code.
7. Refactor hfs_bmap_free() in fs/hfs/btree.c to use the new
   hfs_bmap_clear_bit() helper.
8. In hfs_btree_open(), retrieve the header node via hfs_bnode_find(),
   test its allocation bit with hfs_bmap_test_bit(), and release it
   using hfs_bnode_put().

Suggested-by: Viacheslav Dubeyko <slava@dubeyko.com>
Link: https://lore.kernel.org/all/6a36101b.be22b350.2a3e9.0001.GAE@google.com/T/#r446d0fed2a2900bd805534bbcb799d86619ae2ea
Signed-off-by: Aditya Prakash Srivastava <aditya.ansh182@gmail.com>
Reviewed-by: Viacheslav Dubeyko <slava@dubeyko.com>
Signed-off-by: Viacheslav Dubeyko <slava@dubeyko.com>
Link: https://lore.kernel.org/r/20260716074150.1660-1-aditya.ansh182@gmail.com
Signed-off-by: Viacheslav Dubeyko <slava@dubeyko.com>

...

This commit is contained in:

Aditya Prakash Srivastava 2026-07-16 07:41:50 +00:00 • committed by Viacheslav Dubeyko

parent fdbb95ff89

commit b4160f6325

4 changed files with 218 additions and 87 deletions

Show all changes Ignore whitespace when comparing lines Ignore changes in amount of whitespace Ignore changes in whitespace at EOL

Download patch file Download diff file Expand all files Collapse all files

42

fs/hfs/bnode.c

View file

210

fs/hfs/btree.c

View file

40

fs/hfs/btree.h

View file

13

include/linux/hfs_common.h

View file