Re: [PATCH v2 1/1] hfsplus: validate B-tree record offset table

[Viacheslav Dubeyko <slava@dubeyko.com>]

On Thu, 2026-07-02 at 16:22 +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().
> 
> Reject corrupted B-tree metadata earlier: validate num_recs against
> the node size
> before walking the record offset table, reject record offsets that
> are unordered,
> unaligned, outside the node, or overlapping the offset table, stop B-
> tree record
> walkers on invalid records, and avoid decrementing an already-zero
> leaf_count.
> 
> Closes:
> https://lore.kernel.org/lkml/CANypQFb_2TqKGrztAXj5m0_v...@mail.gmail.com/
> Assisted-by: Codex:gpt-5.5-xhigh
> Signed-off-by: Jiaming Zhang <r772577952@gmail.com>
> ---
>  fs/hfsplus/bfind.c      | 27 ++++++++++++++++--
>  fs/hfsplus/bnode.c      | 16 ++++++++---
>  fs/hfsplus/brec.c       | 37 +++++++++++++++---------
>  fs/hfsplus/hfsplus_fs.h | 62
> +++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 122 insertions(+), 20 deletions(-)
> 
> diff --git a/fs/hfsplus/bfind.c b/fs/hfsplus/bfind.c
> index 9a55fa6d5294..363faf214a1c 100644
> --- a/fs/hfsplus/bfind.c
> +++ b/fs/hfsplus/bfind.c
> @@ -108,15 +108,28 @@ int __hfs_brec_find(struct hfs_bnode *bnode,
> struct hfs_find_data *fd,
>  	int b, e;
>  	int res;
>  
> +	fd->record = -1;
> +	fd->keyoffset = -1;
> +	fd->keylength = -1;
> +	fd->entryoffset = -1;
> +	fd->entrylength = -1;

It looks like static inline function that needs to be re-used
everywhere. And, first of all, it should be called hfs_find_init(). Do
we really need to call this initialization somewhere else? Do you think
that hfs_find_init() if not enough?

> +
>  	BUG_ON(!rec_found);
> +	if (!hfs_bnode_num_recs_valid(bnode)) {
> +		res = -EIO;

Are you sure that it should -EIO but not -ENOENT? Is hfs_brec_find()
ready to process -EIO? There are multiple __hfs_brec_find() calls that
never analyze the return error code. Are we OK with that?

> +		goto fail;

OK. I see. You need this initialization because you are going to fail
case.

> +	}
> +
>  	b = 0;
>  	e = bnode->num_recs - 1;
>  	res = -ENOENT;
> +	if (bnode->num_recs == 0)
> +		goto fail;

Are you sure that we should go to fail? Why should we change the logic
here? I think we can continue the logic even if bnode->num_recs == 0.

>  	do {
>  		rec = (e + b) / 2;
>  		len = hfs_brec_lenoff(bnode, rec, &off);
>  		keylen = hfs_brec_keylen(bnode, rec);
> -		if (keylen == 0) {
> +		if (keylen == 0 || keylen >= len) {

Are you sure that keylen == len is invalid case? What is wrong with
equality?

>  			res = -EINVAL;
>  			goto fail;
>  		}
> @@ -130,7 +143,7 @@ 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 (keylen == 0 || keylen >= len) {

Ditto. What is wrong with equality?

>  			res = -EINVAL;
>  			goto fail;
>  		}
> @@ -232,6 +245,14 @@ int hfs_brec_goto(struct hfs_find_data *fd, int
> cnt)
>  
>  	bnode = fd->bnode;
>  	tree = bnode->tree;
> +	if (!hfs_bnode_num_recs_valid(bnode)) {
> +		res = -EIO;
> +		goto out;
> +	}
> +	if (bnode->num_recs == 0) {
> +		res = -ENOENT;
> +		goto out;
> +	}

I am not completely sure that it is proper place for these checks.
Because, we could work with multiple nodes in this method.

>  
>  	if (cnt < 0) {
>  		cnt = -cnt;
> @@ -274,7 +295,7 @@ 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 (keylen == 0 || keylen >= len) {

Ditto. What is wrong with equality?

>  		res = -EINVAL;
>  		goto out;
>  	}
> diff --git a/fs/hfsplus/bnode.c b/fs/hfsplus/bnode.c
> index d088fb7eb0df..f185c012d090 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_valid(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) {
> @@ -579,6 +586,9 @@ struct hfs_bnode *hfs_bnode_find(struct hfs_btree
> *tree, u32 num)
>  		goto node_error;
>  	}
>  
> +	if (!hfs_bnode_num_recs_valid(node))
> +		goto node_error;
> +
>  	rec_off = tree->node_size - 2;
>  	off = hfs_bnode_read_u16(node, rec_off);
>  	if (off != sizeof(struct hfs_bnode_desc))
> @@ -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_range_valid(node, off, next_off,
> rec_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..fe2e0636798c 100644
> --- a/fs/hfsplus/brec.c
> +++ b/fs/hfsplus/brec.c
> @@ -20,38 +20,44 @@ 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;
>  
> -	dataoff = node->tree->node_size - (rec + 2) * 2;
> -	hfs_bnode_read(node, retval, dataoff, 4);
> +	if (!hfs_brec_record_valid(node, rec)) {
> +		*off = 0;
> +		return 0;
> +	}
> +
> +	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_range_valid(node, *off, next_off, data_off))
> +		return 0;
> +	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_valid(node, rec))
> +		return 0;
>  
>  	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);
> +		len = hfs_brec_lenoff(node, rec, &recoff);
> +		if (len == 0)
>  			return 0;
> -		}
>  
>  		retval = hfs_bnode_read_u16(node, recoff) + 2;
> -		if (retval > node->tree->max_key_len + 2) {
> +		if (retval >= len || retval > node->tree-
> >max_key_len + 2) {
>  			pr_err("keylen %d too large\n",
>  				retval);
>  			retval = 0;
> @@ -185,10 +191,15 @@ int hfs_brec_remove(struct hfs_find_data *fd)
>  	tree = fd->tree;
>  	node = fd->bnode;
>  again:
> +	if (!hfs_brec_record_valid(node, fd->record))
> +		return -EIO;
> +
>  	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 -EIO;
>  		tree->leaf_count--;
>  		mark_inode_dirty(tree->inode);
>  	}
> diff --git a/fs/hfsplus/hfsplus_fs.h b/fs/hfsplus/hfsplus_fs.h
> index ec04b82ad927..7a345c4d1c06 100644
> --- a/fs/hfsplus/hfsplus_fs.h
> +++ b/fs/hfsplus/hfsplus_fs.h
> @@ -587,6 +587,68 @@ bool is_bnode_offset_valid(struct hfs_bnode
> *node, u32 off)
>  	return is_valid;
>  }
>  
> +static inline
> +bool hfs_bnode_num_recs_valid(struct hfs_bnode *node)
> +{
> +	u32 node_size;
> +	u32 rec_off_size;

u32 rec_size = sizeof(__be16);

> +	u32 rec_off_tab_size;
> +	u32 rec_area_size;

Why not?

u32 table_size;
u32 area_size;


> +
> +	if (!node || !node->tree)
> +		return false;
> +
> +	node_size = node->tree->node_size;
> +	rec_off_size = sizeof(__be16);

We don't need it here.

> +	if (node_size < sizeof(struct hfs_bnode_desc) +
> rec_off_size)

Do you really need to add the rec_off_size? Because, you subtract only
sizeof(struct hfs_bnode_desc).

> +		return false;
> +
> +	rec_area_size = node_size - sizeof(struct hfs_bnode_desc);

You reuse sizeof(struct hfs_bnode_desc). We need local variable
instead.

> +	rec_off_tab_size = ((u32)node->num_recs + 1) * rec_off_size;
> +
> +	return rec_off_tab_size <= rec_area_size;
> +}
> +
> +static inline
> +bool hfs_brec_record_valid(struct hfs_bnode *node, int record)
> +{
> +	if (!hfs_bnode_num_recs_valid(node))
> +		return false;
> +	if (record < 0)
> +		return false;
> +
> +	return record < node->num_recs;
> +}
> +
> +static inline
> +bool hfs_brec_range_valid(struct hfs_bnode *node, u16 off, u16
> next_off,
> +			  u16 rec_off)
> +{
> +	u32 rec_off_size;

u32 rec_size = sizeof(__be16);

> +	u32 rec_off_tab_size;

table_size

> +	u32 rec_off_tab_start;

table_start

Thanks,
Slava.

> +
> +	if (!node || !node->tree)
> +		return false;
> +
> +	if (off < sizeof(struct hfs_bnode_desc) || (off & 1))
> +		return false;
> +
> +	if (next_off <= off ||
> +		next_off > node->tree->node_size ||
> +		next_off > rec_off ||
> +		(next_off & 1))
> +		return false;
> +
> +	rec_off_size = sizeof(__be16);
> +	rec_off_tab_size = ((u32)node->num_recs + 1) * rec_off_size;
> +	rec_off_tab_start = node->tree->node_size -
> rec_off_tab_size;
> +	if (next_off > rec_off_tab_start)
> +		return false;
> +
> +	return true;
> +}
> +
>  static inline
>  u32 check_and_correct_requested_length(struct hfs_bnode *node, u32
> off, u32 len)
>  {