From: Shardul Bankar Date: Wed, 18 Mar 2026 07:38:22 +0000 (+0530) Subject: hfsplus: refactor b-tree map page access and add node-type validation X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=a8eed0ba6a4b2f1803ecdfa9f11a4818cf87c474;p=thirdparty%2Flinux.git 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 --- diff --git a/fs/hfsplus/btree.c b/fs/hfsplus/btree.c index 1220a2f227371..64d168347b4bb 100644 --- a/fs/hfsplus/btree.c +++ b/fs/hfsplus/btree.c @@ -129,6 +129,95 @@ u32 hfsplus_calc_btree_clump_size(u32 block_size, u32 node_size, return clump_size; } +/* Context for iterating b-tree map pages + * @page_idx: The index of the page within the b-node's page array + * @off: The byte offset within the mapped page + * @len: The remaining length of the map record + */ +struct hfs_bmap_ctx { + unsigned int page_idx; + unsigned int off; + u16 len; +}; + +/* + * Finds the specific page containing the requested byte offset within the map + * record. Automatically handles the difference between header and map nodes. + * Returns the struct page pointer, or an ERR_PTR on failure. + * Note: The caller is responsible for mapping/unmapping the returned page. + */ +static struct page *hfs_bmap_get_map_page(struct hfs_bnode *node, struct hfs_bmap_ctx *ctx, + u32 byte_offset) +{ + u16 rec_idx, off16; + unsigned int page_off; + + if (node->this == HFSPLUS_TREE_HEAD) { + if (node->type != HFS_NODE_HEADER) { + pr_err("hfsplus: invalid btree header node\n"); + return ERR_PTR(-EIO); + } + rec_idx = HFSPLUS_BTREE_HDR_MAP_REC_INDEX; + } else { + if (node->type != HFS_NODE_MAP) { + pr_err("hfsplus: invalid btree map node\n"); + return ERR_PTR(-EIO); + } + rec_idx = HFSPLUS_BTREE_MAP_NODE_REC_INDEX; + } + + ctx->len = hfs_brec_lenoff(node, rec_idx, &off16); + if (!ctx->len) + return ERR_PTR(-ENOENT); + + if (!is_bnode_offset_valid(node, off16)) + return ERR_PTR(-EIO); + + ctx->len = check_and_correct_requested_length(node, off16, ctx->len); + + if (byte_offset >= ctx->len) + return ERR_PTR(-EINVAL); + + page_off = (u32)off16 + node->page_offset + byte_offset; + ctx->page_idx = page_off >> PAGE_SHIFT; + ctx->off = page_off & ~PAGE_MASK; + + return node->page[ctx->page_idx]; +} + +/** + * hfs_bmap_clear_bit - clear a bit in the b-tree map + * @node: the b-tree node containing the map record + * @node_bit_idx: the relative bit index within the node's map record + * + * Returns 0 on success, -EINVAL if already clear, or negative error code. + */ +static int hfs_bmap_clear_bit(struct hfs_bnode *node, u32 node_bit_idx) +{ + struct hfs_bmap_ctx ctx; + struct page *page; + u8 *bmap, mask; + + page = hfs_bmap_get_map_page(node, &ctx, node_bit_idx / BITS_PER_BYTE); + if (IS_ERR(page)) + return PTR_ERR(page); + + bmap = kmap_local_page(page); + + mask = 1 << (7 - (node_bit_idx % BITS_PER_BYTE)); + + if (!(bmap[ctx.off] & mask)) { + kunmap_local(bmap); + return -EINVAL; + } + + bmap[ctx.off] &= ~mask; + set_page_dirty(page); + kunmap_local(bmap); + + return 0; +} + /* Get a reference to a B*Tree and do some initial checks */ struct hfs_btree *hfs_btree_open(struct super_block *sb, u32 id) { @@ -374,11 +463,9 @@ int hfs_bmap_reserve(struct hfs_btree *tree, u32 rsvd_nodes) struct hfs_bnode *hfs_bmap_alloc(struct hfs_btree *tree) { struct hfs_bnode *node, *next_node; - struct page **pagep; + struct hfs_bmap_ctx ctx; + struct page *page; u32 nidx, idx; - unsigned off; - u16 off16; - u16 len; u8 *data, byte, m; int i, res; @@ -390,30 +477,26 @@ struct hfs_bnode *hfs_bmap_alloc(struct hfs_btree *tree) node = hfs_bnode_find(tree, nidx); if (IS_ERR(node)) return node; - len = hfs_brec_lenoff(node, 2, &off16); - off = off16; - if (!is_bnode_offset_valid(node, off)) { + page = hfs_bmap_get_map_page(node, &ctx, 0); + if (IS_ERR(page)) { + res = PTR_ERR(page); hfs_bnode_put(node); - return ERR_PTR(-EIO); + return ERR_PTR(res); } - len = check_and_correct_requested_length(node, off, len); - off += node->page_offset; - pagep = node->page + (off >> PAGE_SHIFT); - data = kmap_local_page(*pagep); - off &= ~PAGE_MASK; + data = kmap_local_page(page); idx = 0; for (;;) { - while (len) { - byte = data[off]; + while (ctx.len) { + byte = data[ctx.off]; if (byte != 0xff) { for (m = 0x80, i = 0; i < 8; m >>= 1, i++) { if (!(byte & m)) { idx += i; - data[off] |= m; - set_page_dirty(*pagep); + data[ctx.off] |= m; + set_page_dirty(page); kunmap_local(data); tree->free_nodes--; mark_inode_dirty(tree->inode); @@ -423,13 +506,14 @@ struct hfs_bnode *hfs_bmap_alloc(struct hfs_btree *tree) } } } - if (++off >= PAGE_SIZE) { + if (++ctx.off >= PAGE_SIZE) { kunmap_local(data); - data = kmap_local_page(*++pagep); - off = 0; + page = node->page[++ctx.page_idx]; + data = kmap_local_page(page); + ctx.off = 0; } idx += 8; - len--; + ctx.len--; } kunmap_local(data); nidx = node->next; @@ -443,22 +527,22 @@ struct hfs_bnode *hfs_bmap_alloc(struct hfs_btree *tree) return next_node; node = next_node; - len = hfs_brec_lenoff(node, 0, &off16); - off = off16; - off += node->page_offset; - pagep = node->page + (off >> PAGE_SHIFT); - data = kmap_local_page(*pagep); - off &= ~PAGE_MASK; + page = hfs_bmap_get_map_page(node, &ctx, 0); + if (IS_ERR(page)) { + res = PTR_ERR(page); + hfs_bnode_put(node); + return ERR_PTR(res); + } + data = kmap_local_page(page); } } void hfs_bmap_free(struct hfs_bnode *node) { struct hfs_btree *tree; - struct page *page; u16 off, len; u32 nidx; - u8 *data, byte, m; + int res; hfs_dbg("node %u\n", node->this); BUG_ON(!node->this); @@ -495,24 +579,15 @@ void hfs_bmap_free(struct hfs_bnode *node) } len = hfs_brec_lenoff(node, 0, &off); } - off += node->page_offset + nidx / 8; - page = node->page[off >> PAGE_SHIFT]; - data = kmap_local_page(page); - off &= ~PAGE_MASK; - m = 1 << (~nidx & 7); - byte = data[off]; - if (!(byte & m)) { - pr_crit("trying to free free bnode " - "%u(%d)\n", - node->this, node->type); - kunmap_local(data); - hfs_bnode_put(node); - return; + + res = hfs_bmap_clear_bit(node, nidx); + if (res == -EINVAL) { + pr_crit("trying to free free bnode %u(%d)\n", + node->this, node->type); + } else if (!res) { + tree->free_nodes++; + mark_inode_dirty(tree->inode); } - data[off] = byte & ~m; - set_page_dirty(page); - kunmap_local(data); + hfs_bnode_put(node); - tree->free_nodes++; - mark_inode_dirty(tree->inode); } diff --git a/include/linux/hfs_common.h b/include/linux/hfs_common.h index dadb5e0aa8a38..be24c687858e0 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 */