Re: [PATCH v5] hfsplus: validate B-tree record offset table

[Viacheslav Dubeyko <slava@dubeyko.com>]

On Tue, 2026-07-28 at 17:36 -0700, Viacheslav Dubeyko wrote:
> On Tue, 2026-07-28 at 18:12 +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 <r772577952@gmail.com>
> > ---
> > 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      | 14 ++++++--
> >  fs/hfsplus/hfsplus_fs.h | 79
> > +++++++++++++++++++++++++++++++++++++++++
> >  5 files changed, 153 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;
> >  		}
> > @@ -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..b3d6ee78773e 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 +622,11 @@ 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) ||
> > +	    !is_bnode_offset_valid(node, off)) {
> 
> If I am correct, the off value is never used. So, I think that this
> check is not necessary here. Am I right?
> 
> > +		hfs_bnode_put(node);
> 
> I think we cannot keep silence here. I believe that we should have
> the
> error message for this case. Do you agree?
> 
> > +		return;
> > +	}
> >  	while (nidx >= len * 8) {
> >  		u32 i;
> >  
> > @@ -648,6 +653,11 @@ void hfs_bmap_free(struct hfs_bnode *node)
> >  			return;
> >  		}
> >  		len = hfs_brec_lenoff(node, 0, &off);
> > +		if (hfs_brec_len_invalid(node, len) ||
> > +		    !is_bnode_offset_valid(node, off)) {
> 
> Ditto.
> 
> > +			hfs_bnode_put(node);
> 
> Ditto.
> 
> > +			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)
> >  {
> 
> Mostly, I don't see the critical issues in the patch. But some minor
> corrections are necessary. Meanwhile, let me run xfstests for the
> patch.
> 
> 

The xfstests run was successful. The patch hasn't revealed any new
issues. Please, rework the patch as requested.

Thanks,
Slava.