Re: [PATCH v6] hfsplus: validate B-tree record offset table

On Thu, 2026-08-06 at 15:33 +0800, Jiaming Zhang wrote:
> A crafted HFS+ image can contain a corrupted B-tree node. The node
> descriptor may contain a record count that does not fit in the node,
> and
> record offsets may be unordered, unaligned, outside the node, or
> point into
> the offset table itself.
> 
> Several B-tree helpers consume these on-disk fields before validating
> them:
> hfs_bnode_dump() can walk past the offset table when num_recs is
> corrupted,
> hfs_brec_lenoff() can produce an underflowed length or a record range
> that
> overlaps the offset table. This can make the unlink/writeback path
> repeatedly call hfs_bnode_read_u16() with invalid offsets while
> holding the
> HFS+ B-tree lock, producing a flood of "requested invalid offset"
> messages.
> Other writeback workers then block on tree->tree_lock and the system
> reports tasks hung in hfsplus_write_inode().
> 
> Validate num_recs against the node size before walking the record
> offset
> table. Reject record ranges that are unordered, unaligned, outside
> the
> node, or overlapping the offset table. Reject invalid record indexes
> before
> reading their offset entries, and avoid decrementing an already-zero
> leaf_count.
> 
> Closes:
> https://lore.kernel.org/lkml/CANypQFb_2TqKGrztAXj5m0_v+QChxXDnQVeifzV8J25Vuju10Q@mail.gmail.com/
> Assisted-by: Codex:gpt-5.5-xhigh
> Signed-off-by: Jiaming Zhang <[email protected]>
> ---
> Changes in v6:
> - hfs_bmap_free(): Drop offset checks and print error message when B-
> tree
>   map record length is invalid.
> 
> Changes in v5:
> - Switch helpers to invalid checker and invert callers.
> - hfs_brec_offsets_invalid(): Drop the redundant offset-table
> argument
>   since it is already covered by the offset-table overlap check and
> take
>   just the two neighboring record offsets (off and next_off).
> - hfs_brec_len_invalid(): reject a length against node_size.
> - Use hfs_brec_len_invalid() for both length checks in
> hfs_bmap_get_map_page().
> - Validate the record offset in hfs_bmap_free().
> - Check the __hfs_brec_find() return code in [2] and [3]. [1] and [4]
> call
>   it to find the insertion slot for a new index key after a split, -
> ENOENT is
>   one of expected, even -EINVAL the following hfs_brec_insert() just
> inserts
>   at slot 0 of a node already validated by hfs_bnode_find(), so it
> stays
>   in-bounds and cannot trigger the invalid-offset flood. Hence no
> check was
>   added.
> 
> [1]
> https://elixir.bootlin.com/linux/v7.2-rc3/source/fs/hfsplus/brec.c#L160
> [2]
> https://elixir.bootlin.com/linux/v7.2-rc3/source/fs/hfsplus/brec.c#L208
> [3]
> https://elixir.bootlin.com/linux/v7.2-rc3/source/fs/hfsplus/brec.c#L382
> [4]
> https://elixir.bootlin.com/linux/v7.2-rc3/source/fs/hfsplus/brec.c#L449
> 
> Changes in v4:
> - Rename hfs_find_reset() to hfs_find_result_init().
> - Reset find result fields in __hfs_brec_find().
> - Move num_recs validation next to descriptor field initialization.
> - Rename hfs_brec_range_valid() to hfs_brec_offpair_valid().
> - Use U16_MAX for invalid offset/len/keylen sentinels and update
> callers.
> - Add hfs_brec_len_valid() to check validity of len/keylen.
> - Handle invalid B-tree map record lengths in hfs_bmap_get_map_page()
>   and hfs_bmap_free().
> - Return -EINVAL instead of -EIO for invalid remove cursor/leaf_count
> state.
> 
> Changes in v3:
> - Drop the keylen == len check.
> - Drop the explicit zero-record check in __hfs_brec_find().
> - Move find cursor reset into hfs_find_reset() and call it from
> hfs_find_init() and hfs_brec_find().
> - Rename helper-local variables as suggested.
> 
>  fs/hfsplus/bfind.c      | 23 ++++++------
>  fs/hfsplus/bnode.c      | 16 ++++++---
>  fs/hfsplus/brec.c       | 53 ++++++++++++++++++---------
>  fs/hfsplus/btree.c      | 16 +++++++--
>  fs/hfsplus/hfsplus_fs.h | 79
> +++++++++++++++++++++++++++++++++++++++++
>  5 files changed, 155 insertions(+), 32 deletions(-)
> 
> diff --git a/fs/hfsplus/bfind.c b/fs/hfsplus/bfind.c
> index 9a55fa6d5294..ca9813f58a6d 100644
> --- a/fs/hfsplus/bfind.c
> +++ b/fs/hfsplus/bfind.c
> @@ -18,6 +18,7 @@ int hfs_find_init(struct hfs_btree *tree, struct
> hfs_find_data *fd)
>  
>  	fd->tree = tree;
>  	fd->bnode = NULL;
> +	hfs_find_result_init(fd);
>  	ptr = kzalloc(tree->max_key_len * 2 + 4, GFP_KERNEL);
>  	if (!ptr)
>  		return -ENOMEM;
> @@ -106,17 +107,21 @@ int __hfs_brec_find(struct hfs_bnode *bnode,
> struct hfs_find_data *fd,
>  	u16 off, len, keylen;
>  	int rec;
>  	int b, e;
> -	int res;
> +	int res = -ENOENT;
>  
>  	BUG_ON(!rec_found);
> +	hfs_find_result_init(fd);
> +	if (hfs_bnode_num_recs_invalid(bnode))
> +		goto fail;
> +
>  	b = 0;
>  	e = bnode->num_recs - 1;
> -	res = -ENOENT;
>  	do {
>  		rec = (e + b) / 2;
>  		len = hfs_brec_lenoff(bnode, rec, &off);
>  		keylen = hfs_brec_keylen(bnode, rec);
> -		if (keylen == 0) {
> +		if (hfs_brec_len_invalid(bnode, len) ||
> +		    hfs_brec_len_invalid(bnode, keylen)) {
>  			res = -EINVAL;
>  			goto fail;
>  		}


I've realized that we have additional issue in HFS+ logic. Potentially,
keylen and len could be not invalid but we could have negative value
later in the logic:

done:
	fd->record = e;
	fd->keyoffset = off;
	fd->keylength = keylen;
	fd->entryoffset = off + keylen;
	fd->entrylength = len - keylen; <-- negative value here.

The negative value of fd->entrylength is checked in multiple places.
However, there is extents tree logic that has no such check [1]:

static int __hfsplus_ext_write_extent(struct inode *inode,
		struct hfs_find_data *fd)
{
<skipped>

	} else {
		if (res)
			return res;
		hfs_bnode_write(fd->bnode, hip->cached_extents,
				fd->entryoffset, fd->entrylength);
		hip->extent_state &= ~HFSPLUS_EXT_DIRTY;
	}

<skipped>
}

Could you please double check my conclusion? We can fix the issue in
another patch. Could you please fix the issue?

> @@ -130,7 +135,8 @@ int __hfs_brec_find(struct hfs_bnode *bnode,
> struct hfs_find_data *fd,
>  	if (rec != e && e >= 0) {
>  		len = hfs_brec_lenoff(bnode, e, &off);
>  		keylen = hfs_brec_keylen(bnode, e);
> -		if (keylen == 0) {
> +		if (hfs_brec_len_invalid(bnode, keylen) ||
> +		    hfs_brec_len_invalid(bnode, len)) {
>  			res = -EINVAL;
>  			goto fail;
>  		}
> @@ -158,11 +164,7 @@ int hfs_brec_find(struct hfs_find_data *fd,
> search_strategy_t do_key_compare)
>  	__be32 data;
>  	int height, res;
>  
> -	fd->record = -1;
> -	fd->keyoffset = -1;
> -	fd->keylength = -1;
> -	fd->entryoffset = -1;
> -	fd->entrylength = -1;
> +	hfs_find_result_init(fd);
>  
>  	tree = fd->tree;
>  	if (fd->bnode)
> @@ -274,7 +276,8 @@ int hfs_brec_goto(struct hfs_find_data *fd, int
> cnt)
>  
>  	len = hfs_brec_lenoff(bnode, fd->record, &off);
>  	keylen = hfs_brec_keylen(bnode, fd->record);
> -	if (keylen == 0) {
> +	if (hfs_brec_len_invalid(bnode, len) ||
> +	    hfs_brec_len_invalid(bnode, keylen)) {
>  		res = -EINVAL;
>  		goto out;
>  	}
> diff --git a/fs/hfsplus/bnode.c b/fs/hfsplus/bnode.c
> index d088fb7eb0df..3a1a1fa6f2e2 100644
> --- a/fs/hfsplus/bnode.c
> +++ b/fs/hfsplus/bnode.c
> @@ -352,15 +352,22 @@ void hfs_bnode_dump(struct hfs_bnode *node)
>  	struct hfs_bnode_desc desc;
>  	__be32 cnid;
>  	int i, off, key_off;
> +	u16 num_recs;
>  
>  	hfs_dbg("node %d\n", node->this);
>  	hfs_bnode_read(node, &desc, 0, sizeof(desc));
> +	num_recs = node->num_recs;
>  	hfs_dbg("next %d, prev %d, type %d, height %d, num_recs
> %d\n",
>  		be32_to_cpu(desc.next), be32_to_cpu(desc.prev),
>  		desc.type, desc.height, be16_to_cpu(desc.num_recs));
>  
> +	if (hfs_bnode_num_recs_invalid(node)) {
> +		hfs_dbg("invalid num_recs %u\n", num_recs);
> +		return;
> +	}
> +
>  	off = node->tree->node_size - 2;
> -	for (i = be16_to_cpu(desc.num_recs); i >= 0; off -= 2, i--)
> {
> +	for (i = num_recs; i >= 0; off -= 2, i--) {
>  		key_off = hfs_bnode_read_u16(node, off);
>  		hfs_dbg(" key_off %d", key_off);
>  		if (i && node->type == HFS_NODE_INDEX) {
> @@ -561,6 +568,9 @@ struct hfs_bnode *hfs_bnode_find(struct hfs_btree
> *tree, u32 num)
>  	node->height = desc->height;
>  	kunmap_local(desc);
>  
> +	if (hfs_bnode_num_recs_invalid(node))
> +		goto node_error;
> +
>  	switch (node->type) {
>  	case HFS_NODE_HEADER:
>  	case HFS_NODE_MAP:
> @@ -586,9 +596,7 @@ struct hfs_bnode *hfs_bnode_find(struct hfs_btree
> *tree, u32 num)
>  	for (i = 1; i <= node->num_recs; off = next_off, i++) {
>  		rec_off -= 2;
>  		next_off = hfs_bnode_read_u16(node, rec_off);
> -		if (next_off <= off ||
> -		    next_off > tree->node_size ||
> -		    next_off & 1)
> +		if (hfs_brec_offsets_invalid(node, off, next_off))
>  			goto node_error;
>  		entry_size = next_off - off;
>  		if (node->type != HFS_NODE_INDEX &&
> diff --git a/fs/hfsplus/brec.c b/fs/hfsplus/brec.c
> index e3df89284079..f416e562d439 100644
> --- a/fs/hfsplus/brec.c
> +++ b/fs/hfsplus/brec.c
> @@ -9,6 +9,8 @@
>   * Handle individual btree records
>   */
>  
> +#include <linux/limits.h>
> +
>  #include "hfsplus_fs.h"
>  #include "hfsplus_raw.h"
>  
> @@ -20,41 +22,49 @@ static int hfs_btree_inc_height(struct hfs_btree
> *);
>  u16 hfs_brec_lenoff(struct hfs_bnode *node, u16 rec, u16 *off)
>  {
>  	__be16 retval[2];
> -	u16 dataoff;
> +	u16 data_off;
> +	u16 next_off;
> +
> +	if (hfs_brec_record_invalid(node, rec)) {
> +		*off = U16_MAX;
> +		return U16_MAX;
> +	}
>  
> -	dataoff = node->tree->node_size - (rec + 2) * 2;
> -	hfs_bnode_read(node, retval, dataoff, 4);
> +	data_off = node->tree->node_size - (rec + 2) * 2;
> +	hfs_bnode_read(node, retval, data_off, 4);
>  	*off = be16_to_cpu(retval[1]);
> -	return be16_to_cpu(retval[0]) - *off;
> +	next_off = be16_to_cpu(retval[0]);
> +	if (hfs_brec_offsets_invalid(node, *off, next_off)) {
> +		*off = U16_MAX;
> +		return U16_MAX;
> +	}
> +	return next_off - *off;
>  }
>  
>  /* Get the length of the key from a keyed record */
>  u16 hfs_brec_keylen(struct hfs_bnode *node, u16 rec)
>  {
> -	u16 retval, recoff;
> +	u16 retval, recoff, len;
>  
>  	if (node->type != HFS_NODE_INDEX && node->type !=
> HFS_NODE_LEAF)
>  		return 0;
> +	if (hfs_brec_record_invalid(node, rec))
> +		return U16_MAX;
>  
>  	if ((node->type == HFS_NODE_INDEX) &&
>  	   !(node->tree->attributes & HFS_TREE_VARIDXKEYS) &&
>  	   (node->tree->cnid != HFSPLUS_ATTR_CNID)) {
>  		retval = node->tree->max_key_len + 2;
>  	} else {
> -		recoff = hfs_bnode_read_u16(node,
> -			node->tree->node_size - (rec + 1) * 2);
> -		if (!recoff)
> -			return 0;
> -		if (recoff > node->tree->node_size - 2) {
> -			pr_err("recoff %d too large\n", recoff);
> -			return 0;
> -		}
> +		len = hfs_brec_lenoff(node, rec, &recoff);
> +		if (hfs_brec_len_invalid(node, len))
> +			return len;
>  
>  		retval = hfs_bnode_read_u16(node, recoff) + 2;
>  		if (retval > node->tree->max_key_len + 2) {
>  			pr_err("keylen %d too large\n",
>  				retval);
> -			retval = 0;
> +			retval = U16_MAX;
>  		}
>  	}
>  	return retval;
> @@ -181,14 +191,20 @@ int hfs_brec_remove(struct hfs_find_data *fd)
>  	struct hfs_btree *tree;
>  	struct hfs_bnode *node, *parent;
>  	int end_off, rec_off, data_off, size;
> +	int res;
>  
>  	tree = fd->tree;
>  	node = fd->bnode;
>  again:
> +	if (hfs_brec_record_invalid(node, fd->record))
> +		return -EINVAL;
> +
>  	rec_off = tree->node_size - (fd->record + 2) * 2;
>  	end_off = tree->node_size - (node->num_recs + 1) * 2;
>  
>  	if (node->type == HFS_NODE_LEAF) {
> +		if (tree->leaf_count == 0)
> +			return -EINVAL;
>  		tree->leaf_count--;
>  		mark_inode_dirty(tree->inode);
>  	}
> @@ -205,7 +221,9 @@ int hfs_brec_remove(struct hfs_find_data *fd)
>  		hfs_bnode_put(node);
>  		node = fd->bnode = parent;
>  
> -		__hfs_brec_find(node, fd, hfs_find_rec_by_key);
> +		res = __hfs_brec_find(node, fd,
> hfs_find_rec_by_key);
> +		if (res && res != -ENOENT)
> +			return res;
>  		goto again;
>  	}
>  	hfs_bnode_write_u16(node,
> @@ -368,6 +386,7 @@ static int hfs_brec_update_parent(struct
> hfs_find_data *fd)
>  	int newkeylen, diff;
>  	int rec, rec_off, end_rec_off;
>  	int start_off, end_off;
> +	int res;
>  
>  	tree = fd->tree;
>  	node = fd->bnode;
> @@ -379,7 +398,9 @@ static int hfs_brec_update_parent(struct
> hfs_find_data *fd)
>  	parent = hfs_bnode_find(tree, node->parent);
>  	if (IS_ERR(parent))
>  		return PTR_ERR(parent);
> -	__hfs_brec_find(parent, fd, hfs_find_rec_by_key);
> +	res = __hfs_brec_find(parent, fd, hfs_find_rec_by_key);
> +	if (res && res != -ENOENT)
> +		return res;
>  	if (fd->record < 0)
>  		return -ENOENT;
>  	hfs_bnode_dump(parent);
> diff --git a/fs/hfsplus/btree.c b/fs/hfsplus/btree.c
> index 394542a47e60..2ea8cd5658e1 100644
> --- a/fs/hfsplus/btree.c
> +++ b/fs/hfsplus/btree.c
> @@ -168,8 +168,8 @@ static struct page *hfs_bmap_get_map_page(struct
> hfs_bnode *node,
>  	}
>  
>  	ctx->len = hfs_brec_lenoff(node, rec_idx, &off16);
> -	if (!ctx->len)
> -		return ERR_PTR(-ENOENT);
> +	if (hfs_brec_len_invalid(node, ctx->len))
> +		return ERR_PTR(-EINVAL);
>  
>  	if (!is_bnode_offset_valid(node, off16))
>  		return ERR_PTR(-EIO);
> @@ -622,6 +622,12 @@ void hfs_bmap_free(struct hfs_bnode *node)
>  	if (IS_ERR(node))
>  		return;
>  	len = hfs_brec_lenoff(node, 2, &off);
> +	if (hfs_brec_len_invalid(node, len)) {
> +		pr_err("invalid bmap record length: node %u, len
> %u\n",
> +		       node->this, len);
> +		hfs_bnode_put(node);
> +		return;
> +	}
>  	while (nidx >= len * 8) {
>  		u32 i;
>  
> @@ -648,6 +654,12 @@ void hfs_bmap_free(struct hfs_bnode *node)
>  			return;
>  		}
>  		len = hfs_brec_lenoff(node, 0, &off);
> +		if (hfs_brec_len_invalid(node, len)) {
> +			pr_err("invalid bmap record length: node %u,
> len %u\n",
> +			       node->this, len);
> +			hfs_bnode_put(node);
> +			return;
> +		}
>  	}
>  
>  	res = hfs_bmap_clear_bit(node, nidx);
> diff --git a/fs/hfsplus/hfsplus_fs.h b/fs/hfsplus/hfsplus_fs.h
> index ec04b82ad927..90fcf1eac913 100644
> --- a/fs/hfsplus/hfsplus_fs.h
> +++ b/fs/hfsplus/hfsplus_fs.h
> @@ -587,6 +587,85 @@ bool is_bnode_offset_valid(struct hfs_bnode
> *node, u32 off)
>  	return is_valid;
>  }
>  
> +static inline
> +bool hfs_bnode_num_recs_invalid(struct hfs_bnode *node)
> +{
> +	u32 node_size;
> +	u32 table_size;
> +	u32 area_size;
> +	u32 rec_size = sizeof(__be16);
> +	u32 desc_size = sizeof(struct hfs_bnode_desc);
> +
> +	if (!node || !node->tree)
> +		return true;
> +
> +	node_size = node->tree->node_size;
> +	if (node_size < desc_size)
> +		return true;
> +
> +	area_size = node_size - desc_size;
> +	table_size = ((u32)node->num_recs + 1) * rec_size;
> +
> +	return table_size > area_size;
> +}
> +
> +static inline
> +bool hfs_brec_record_invalid(struct hfs_bnode *node, int record)
> +{
> +	if (hfs_bnode_num_recs_invalid(node))
> +		return true;
> +	if (record < 0)
> +		return true;
> +
> +	return record >= node->num_recs;
> +}
> +
> +static inline
> +bool hfs_brec_offsets_invalid(struct hfs_bnode *node, u16 off, u16
> next_off)
> +{
> +	u32 table_size;
> +	u32 table_start;
> +	u32 rec_size = sizeof(__be16);
> +	u32 desc_size = sizeof(struct hfs_bnode_desc);
> +
> +	if (!node || !node->tree)
> +		return true;
> +
> +	if (off < desc_size || (off & 1))
> +		return true;
> +
> +	if (next_off <= off ||
> +	    next_off > node->tree->node_size ||
> +	    (next_off & 1))
> +		return true;
> +
> +	table_size = ((u32)node->num_recs + 1) * rec_size;
> +	table_start = node->tree->node_size - table_size;
> +	if (next_off > table_start)
> +		return true;
> +
> +	return false;
> +}
> +
> +static inline
> +bool hfs_brec_len_invalid(struct hfs_bnode *node, u16 len)
> +{
> +	if (!node || !node->tree)
> +		return true;
> +
> +	return len == 0 || len > node->tree->node_size;
> +}
> +
> +static inline
> +void hfs_find_result_init(struct hfs_find_data *fd)
> +{
> +	fd->record = -1;
> +	fd->keyoffset = -1;
> +	fd->keylength = -1;
> +	fd->entryoffset = -1;
> +	fd->entrylength = -1;
> +}
> +
>  static inline
>  u32 check_and_correct_requested_length(struct hfs_bnode *node, u32
> off, u32 len)
>  {

Looks good.

Reviewed-by: Viacheslav Dubeyko <[email protected]>
Tested-by: Viacheslav Dubeyko <[email protected]>

[1]
https://elixir.bootlin.com/linux/v7.2-rc6/source/fs/hfsplus/extents.c#L113

Thanks,
Slava.