From a8eed0ba6a4b2f1803ecdfa9f11a4818cf87c474 Mon Sep 17 00:00:00 2001 From: Shardul Bankar Date: Wed, 18 Mar 2026 13:08:22 +0530 Subject: hfsplus: refactor b-tree map page access and add node-type validation In HFS+ b-trees, the node allocation bitmap is stored across multiple records. The first chunk resides in the b-tree Header Node at record index 2, while all subsequent chunks are stored in dedicated Map Nodes at record index 0. This structural quirk forces callers like hfs_bmap_alloc() and hfs_bmap_free() to duplicate boilerplate code to validate offsets, correct lengths, and map the underlying pages via kmap_local_page(). There is also currently no strict node-type validation before reading these records, leaving the allocator vulnerable if a corrupted image points a map linkage to an Index or Leaf node. Introduce a unified bit-level API to encapsulate the map record access: 1. A new `struct hfs_bmap_ctx` to cleanly pass state and safely handle page math across all architectures. 2. `hfs_bmap_get_map_page()`: Automatically validates node types (HFS_NODE_HEADER vs HFS_NODE_MAP), infers the correct record index, handles page-boundary math, and returns the unmapped `struct page *` directly to the caller to avoid asymmetric mappings. 3. `hfs_bmap_clear_bit()`: A clean wrapper that internally handles page mapping/unmapping for single-bit operations. Refactor hfs_bmap_alloc() and hfs_bmap_free() to utilize this new API. This deduplicates the allocator logic, hardens the map traversal against fuzzed images, and provides the exact abstractions needed for upcoming mount-time validation checks. Signed-off-by: Shardul Bankar Reviewed-by: Viacheslav Dubeyko Tested-by: Viacheslav Dubeyko Signed-off-by: Viacheslav Dubeyko Link: https://lore.kernel.org/r/20260318073823.3933718-2-shardul.b@mpiricsoftware.com Signed-off-by: Viacheslav Dubeyko --- include/linux/hfs_common.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'include/linux') diff --git a/include/linux/hfs_common.h b/include/linux/hfs_common.h index dadb5e0aa8a3..be24c687858e 100644 --- a/include/linux/hfs_common.h +++ b/include/linux/hfs_common.h @@ -510,6 +510,8 @@ struct hfs_btree_header_rec { #define HFSPLUS_NODE_MXSZ 32768 #define HFSPLUS_ATTR_TREE_NODE_SIZE 8192 #define HFSPLUS_BTREE_HDR_NODE_RECS_COUNT 3 +#define HFSPLUS_BTREE_HDR_MAP_REC_INDEX 2 /* Map (bitmap) record in Header node */ +#define HFSPLUS_BTREE_MAP_NODE_REC_INDEX 0 /* Map record in Map Node */ #define HFSPLUS_BTREE_HDR_USER_BYTES 128 /* btree key type */ -- cgit v1.2.3