[PATCH v3 RESEND] hfs: validate catalog CNIDs before instantiating inodes

[PATCH v3 RESEND] hfs: validate catalog CNIDs before instantiating inodes

[David Maximiliano Hermitte]

hfs_cat_find_brec() first resolves a catalog thread record by CNID and
then looks up the corresponding catalog record by parent/name. On a
corrupted filesystem image, the second lookup may find a record whose
CNID does not match the CNID that was requested.

Validate the catalog record found by the second lookup before returning
it to callers. Inspect the already-found record with hfs_bnode_read(),
not hfs_brec_read(), and reject records whose CNID is invalid for their
record type or does not match the requested CNID.

Also validate CNIDs in hfs_read_inode() before the inode is populated,
and propagate hfs_read_inode() errors from the resource-fork lookup path.
For the root inode path, require the root catalog record to be a directory
with DirID == HFS_ROOT_CNID, and drop the root inode reference if it was
instantiated as a bad inode.

This keeps hfs_write_inode() unchanged and prevents corrupted catalog
records from reaching the existing reserved-CNID BUG() path during
writeback.

Reported-by: syzbot+97e301b4b82ae803d21b@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=97e301b4b82ae803d21b
Cc: George Anthony Vernon <contact@gvernon.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: David Maximiliano Hermitte <davemadmaxxx@gmail.com>
---
Changes in v3:
- Drop the stray blank line before assigning the hfs_read_inode() result
  in hfs_file_lookup().

Changes in v2:
- Use size_t for the catalog record length.
- Return -EIO when fd->entrylength is larger than hfs_cat_rec instead of
  truncating the record length.
- Compare catalog record lengths against sizeof(struct hfs_cat_file) and
  sizeof(struct hfs_cat_dir).
- Drop the hfs_is_valid_cnid() call from the found-record CNID
  comparison; found_cnid != cnid is enough there.
- Treat non-file/non-directory records found by the second lookup as
  invalid for this path.
- Check is_bad_inode() in the resource-fork lookup error path.
- Drop the redundant root DirID check from hfs_fill_super().

 fs/hfs/catalog.c | 44 +++++++++++++++++++++++++++++++++++++++++++-
 fs/hfs/hfs_fs.h  | 19 +++++++++++++++++++
 fs/hfs/inode.c   | 12 +++++++++---
 fs/hfs/super.c   |  5 +++++
 4 files changed, 76 insertions(+), 4 deletions(-)

diff --git a/fs/hfs/catalog.c b/fs/hfs/catalog.c
index 1bfa36d71e24..50ee709d966f 100644
--- a/fs/hfs/catalog.c
+++ b/fs/hfs/catalog.c
@@ -182,6 +182,43 @@ int hfs_cat_keycmp(const btree_key *key1, const btree_key *key2)
 			  key2->cat.CName.name, key2->cat.CName.len);
 }
 
+static int hfs_cat_validate_found_cnid(struct hfs_find_data *fd, u32 cnid)
+{
+	hfs_cat_rec rec;
+	u32 found_cnid;
+	size_t rec_len;
+
+	if (fd->entrylength <= 0)
+		return -EIO;
+
+	rec_len = fd->entrylength;
+	if (rec_len > sizeof(rec))
+		return -EIO;
+
+	memset(&rec, 0, sizeof(rec));
+	hfs_bnode_read(fd->bnode, &rec, fd->entryoffset, rec_len);
+
+	switch (rec.type) {
+	case HFS_CDR_FIL:
+		if (rec_len < sizeof(struct hfs_cat_file))
+			return -EIO;
+		found_cnid = be32_to_cpu(rec.file.FlNum);
+		break;
+	case HFS_CDR_DIR:
+		if (rec_len < sizeof(struct hfs_cat_dir))
+			return -EIO;
+		found_cnid = be32_to_cpu(rec.dir.DirID);
+		break;
+	default:
+		return -EIO;
+	}
+
+	if (found_cnid != cnid)
+		return -EIO;
+
+	return 0;
+}
+
 /* Try to get a catalog entry for given catalog id */
 // move to read_super???
 int hfs_cat_find_brec(struct super_block *sb, u32 cnid,
@@ -208,7 +245,12 @@ int hfs_cat_find_brec(struct super_block *sb, u32 cnid,
 		return -EIO;
 	}
 	memcpy(fd->search_key->cat.CName.name, rec.thread.CName.name, len);
-	return hfs_brec_find(fd);
+
+	res = hfs_brec_find(fd);
+	if (res)
+		return res;
+
+	return hfs_cat_validate_found_cnid(fd, cnid);
 }
 
 static inline
diff --git a/fs/hfs/hfs_fs.h b/fs/hfs/hfs_fs.h
index f3624514fcb0..670638f17438 100644
--- a/fs/hfs/hfs_fs.h
+++ b/fs/hfs/hfs_fs.h
@@ -155,6 +155,25 @@ extern int hfs_cat_move(u32 cnid, struct inode *src_dir,
 extern void hfs_cat_build_key(struct super_block *sb, btree_key *key,
 			      u32 parent, const struct qstr *name);
 
+/*
+ * Validate the CNID of a catalog record.
+ */
+static inline bool hfs_is_valid_cnid(u32 cnid, u8 type)
+{
+	if (likely(cnid >= HFS_FIRSTUSER_CNID))
+		return true;
+
+	switch (cnid) {
+	case HFS_ROOT_CNID:
+		return type == HFS_CDR_DIR;
+	case HFS_EXT_CNID:
+	case HFS_CAT_CNID:
+		return type == HFS_CDR_FIL;
+	default:
+		return false;
+	}
+}
+
 /* dir.c */
 extern const struct file_operations hfs_dir_operations;
 extern const struct inode_operations hfs_dir_inode_operations;
diff --git a/fs/hfs/inode.c b/fs/hfs/inode.c
index ac4a9055c5c0..ee10a9257a13 100644
--- a/fs/hfs/inode.c
+++ b/fs/hfs/inode.c
@@ -367,6 +367,9 @@ static int hfs_read_inode(struct inode *inode, void *data)
 	rec = idata->rec;
 	switch (rec->type) {
 	case HFS_CDR_FIL:
+		if (!hfs_is_valid_cnid(be32_to_cpu(rec->file.FlNum), rec->type))
+			return -EIO;
+
 		if (!HFS_IS_RSRC(inode)) {
 			hfs_inode_read_fork(inode, rec->file.ExtRec, rec->file.LgLen,
 					    rec->file.PyLen, be16_to_cpu(rec->file.ClpSize));
@@ -390,6 +393,9 @@ static int hfs_read_inode(struct inode *inode, void *data)
 		inode->i_mapping->a_ops = &hfs_aops;
 		break;
 	case HFS_CDR_DIR:
+		if (!hfs_is_valid_cnid(be32_to_cpu(rec->dir.DirID), rec->type))
+			return -EIO;
+
 		inode->i_ino = be32_to_cpu(rec->dir.DirID);
 		inode->i_size = be16_to_cpu(rec->dir.Val) + 2;
 		HFS_I(inode)->fs_blocks = 0;
@@ -571,12 +577,12 @@ static struct dentry *hfs_file_lookup(struct inode *dir, struct dentry *dentry,
 	res = hfs_brec_read(&fd, &rec, sizeof(rec));
 	if (!res) {
 		struct hfs_iget_data idata = { NULL, &rec };
-		hfs_read_inode(inode, &idata);
+		res = hfs_read_inode(inode, &idata);
 	}
 	hfs_find_exit(&fd);
-	if (res) {
+	if (res || is_bad_inode(inode)) {
 		iput(inode);
-		return ERR_PTR(res);
+		return ERR_PTR(-EIO);
 	}
 	HFS_I(inode)->rsrc_inode = dir;
 	HFS_I(dir)->rsrc_inode = inode;
diff --git a/fs/hfs/super.c b/fs/hfs/super.c
index a466c401f6bb..98b80795bcde 100644
--- a/fs/hfs/super.c
+++ b/fs/hfs/super.c
@@ -372,6 +372,11 @@ static int hfs_fill_super(struct super_block *sb, struct fs_context *fc)
 	if (!root_inode)
 		goto bail_no_root;
 
+	if (is_bad_inode(root_inode)) {
+		iput(root_inode);
+		goto bail_no_root;
+	}
+
 	set_default_d_op(sb, &hfs_dentry_operations);
 	res = -ENOMEM;
 	sb->s_root = d_make_root(root_inode);
-- 
2.43.0

Re: [PATCH v3 RESEND] hfs: validate catalog CNIDs before instantiating inodes

[Viacheslav Dubeyko]

On Mon, 2026-07-06 at 09:59 +0000, David Maximiliano Hermitte wrote:
> hfs_cat_find_brec() first resolves a catalog thread record by CNID
> and
> then looks up the corresponding catalog record by parent/name. On a
> corrupted filesystem image, the second lookup may find a record whose
> CNID does not match the CNID that was requested.
> 
> Validate the catalog record found by the second lookup before
> returning
> it to callers. Inspect the already-found record with
> hfs_bnode_read(),
> not hfs_brec_read(), and reject records whose CNID is invalid for
> their
> record type or does not match the requested CNID.
> 
> Also validate CNIDs in hfs_read_inode() before the inode is
> populated,
> and propagate hfs_read_inode() errors from the resource-fork lookup
> path.
> For the root inode path, require the root catalog record to be a
> directory
> with DirID == HFS_ROOT_CNID, and drop the root inode reference if it
> was
> instantiated as a bad inode.
> 
> This keeps hfs_write_inode() unchanged and prevents corrupted catalog
> records from reaching the existing reserved-CNID BUG() path during
> writeback.
> 
> Reported-by: syzbot+97e301b4b82ae803d21b@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=97e301b4b82ae803d21b
> Cc: George Anthony Vernon <contact@gvernon.com>
> Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Signed-off-by: David Maximiliano Hermitte <davemadmaxxx@gmail.com>
> ---
> Changes in v3:
> - Drop the stray blank line before assigning the hfs_read_inode()
> result
>   in hfs_file_lookup().
> 
> Changes in v2:
> - Use size_t for the catalog record length.
> - Return -EIO when fd->entrylength is larger than hfs_cat_rec instead
> of
>   truncating the record length.
> - Compare catalog record lengths against sizeof(struct hfs_cat_file)
> and
>   sizeof(struct hfs_cat_dir).
> - Drop the hfs_is_valid_cnid() call from the found-record CNID
>   comparison; found_cnid != cnid is enough there.
> - Treat non-file/non-directory records found by the second lookup as
>   invalid for this path.
> - Check is_bad_inode() in the resource-fork lookup error path.
> - Drop the redundant root DirID check from hfs_fill_super().
> 
>  fs/hfs/catalog.c | 44 +++++++++++++++++++++++++++++++++++++++++++-
>  fs/hfs/hfs_fs.h  | 19 +++++++++++++++++++
>  fs/hfs/inode.c   | 12 +++++++++---
>  fs/hfs/super.c   |  5 +++++
>  4 files changed, 76 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/hfs/catalog.c b/fs/hfs/catalog.c
> index 1bfa36d71e24..50ee709d966f 100644
> --- a/fs/hfs/catalog.c
> +++ b/fs/hfs/catalog.c
> @@ -182,6 +182,43 @@ int hfs_cat_keycmp(const btree_key *key1, const
> btree_key *key2)
>  			  key2->cat.CName.name, key2-
> >cat.CName.len);
>  }
>  
> +static int hfs_cat_validate_found_cnid(struct hfs_find_data *fd, u32
> cnid)
> +{
> +	hfs_cat_rec rec;
> +	u32 found_cnid;
> +	size_t rec_len;
> +
> +	if (fd->entrylength <= 0)
> +		return -EIO;
> +
> +	rec_len = fd->entrylength;
> +	if (rec_len > sizeof(rec))
> +		return -EIO;

Why do not have one check?

rec_len = fd->entrylength;
if (rec_len <= 0 || rec_len > sizeof(rec))
    return -EIO;

> +
> +	memset(&rec, 0, sizeof(rec));
> +	hfs_bnode_read(fd->bnode, &rec, fd->entryoffset, rec_len);
> +
> +	switch (rec.type) {
> +	case HFS_CDR_FIL:
> +		if (rec_len < sizeof(struct hfs_cat_file))

rec_len != sizeof(struct hfs_cat_file)?

> +			return -EIO;
> +		found_cnid = be32_to_cpu(rec.file.FlNum);
> +		break;
> +	case HFS_CDR_DIR:
> +		if (rec_len < sizeof(struct hfs_cat_dir))

rec_len != sizeof(struct hfs_cat_dir)?

> +			return -EIO;
> +		found_cnid = be32_to_cpu(rec.dir.DirID);
> +		break;
> +	default:
> +		return -EIO;
> +	}
> +
> +	if (found_cnid != cnid)
> +		return -EIO;
> +
> +	return 0;
> +}
> +
>  /* Try to get a catalog entry for given catalog id */
>  // move to read_super???
>  int hfs_cat_find_brec(struct super_block *sb, u32 cnid,
> @@ -208,7 +245,12 @@ int hfs_cat_find_brec(struct super_block *sb,
> u32 cnid,
>  		return -EIO;
>  	}
>  	memcpy(fd->search_key->cat.CName.name,
> rec.thread.CName.name, len);
> -	return hfs_brec_find(fd);
> +
> +	res = hfs_brec_find(fd);
> +	if (res)
> +		return res;
> +
> +	return hfs_cat_validate_found_cnid(fd, cnid);
>  }
>  
>  static inline
> diff --git a/fs/hfs/hfs_fs.h b/fs/hfs/hfs_fs.h
> index f3624514fcb0..670638f17438 100644
> --- a/fs/hfs/hfs_fs.h
> +++ b/fs/hfs/hfs_fs.h
> @@ -155,6 +155,25 @@ extern int hfs_cat_move(u32 cnid, struct inode
> *src_dir,
>  extern void hfs_cat_build_key(struct super_block *sb, btree_key
> *key,
>  			      u32 parent, const struct qstr *name);
>  
> +/*
> + * Validate the CNID of a catalog record.
> + */
> +static inline bool hfs_is_valid_cnid(u32 cnid, u8 type)
> +{
> +	if (likely(cnid >= HFS_FIRSTUSER_CNID))
> +		return true;
> +
> +	switch (cnid) {
> +	case HFS_ROOT_CNID:
> +		return type == HFS_CDR_DIR;
> +	case HFS_EXT_CNID:
> +	case HFS_CAT_CNID:
> +		return type == HFS_CDR_FIL;
> +	default:
> +		return false;
> +	}
> +}
> +
>  /* dir.c */
>  extern const struct file_operations hfs_dir_operations;
>  extern const struct inode_operations hfs_dir_inode_operations;
> diff --git a/fs/hfs/inode.c b/fs/hfs/inode.c
> index ac4a9055c5c0..ee10a9257a13 100644
> --- a/fs/hfs/inode.c
> +++ b/fs/hfs/inode.c
> @@ -367,6 +367,9 @@ static int hfs_read_inode(struct inode *inode,
> void *data)

Have you decided not to have the hfs_is_valid_cnid() for the case of
hfs_write_inode()?

Thanks,
Slava.

>  	rec = idata->rec;
>  	switch (rec->type) {
>  	case HFS_CDR_FIL:
> +		if (!hfs_is_valid_cnid(be32_to_cpu(rec->file.FlNum),
> rec->type))
> +			return -EIO;
> +
>  		if (!HFS_IS_RSRC(inode)) {
>  			hfs_inode_read_fork(inode, rec->file.ExtRec,
> rec->file.LgLen,
>  					    rec->file.PyLen,
> be16_to_cpu(rec->file.ClpSize));
> @@ -390,6 +393,9 @@ static int hfs_read_inode(struct inode *inode,
> void *data)
>  		inode->i_mapping->a_ops = &hfs_aops;
>  		break;
>  	case HFS_CDR_DIR:
> +		if (!hfs_is_valid_cnid(be32_to_cpu(rec->dir.DirID),
> rec->type))
> +			return -EIO;
> +
>  		inode->i_ino = be32_to_cpu(rec->dir.DirID);
>  		inode->i_size = be16_to_cpu(rec->dir.Val) + 2;
>  		HFS_I(inode)->fs_blocks = 0;
> @@ -571,12 +577,12 @@ static struct dentry *hfs_file_lookup(struct
> inode *dir, struct dentry *dentry,
>  	res = hfs_brec_read(&fd, &rec, sizeof(rec));
>  	if (!res) {
>  		struct hfs_iget_data idata = { NULL, &rec };
> -		hfs_read_inode(inode, &idata);
> +		res = hfs_read_inode(inode, &idata);
>  	}
>  	hfs_find_exit(&fd);
> -	if (res) {
> +	if (res || is_bad_inode(inode)) {
>  		iput(inode);
> -		return ERR_PTR(res);
> +		return ERR_PTR(-EIO);
>  	}
>  	HFS_I(inode)->rsrc_inode = dir;
>  	HFS_I(dir)->rsrc_inode = inode;
> diff --git a/fs/hfs/super.c b/fs/hfs/super.c
> index a466c401f6bb..98b80795bcde 100644
> --- a/fs/hfs/super.c
> +++ b/fs/hfs/super.c
> @@ -372,6 +372,11 @@ static int hfs_fill_super(struct super_block
> *sb, struct fs_context *fc)
>  	if (!root_inode)
>  		goto bail_no_root;
>  
> +	if (is_bad_inode(root_inode)) {
> +		iput(root_inode);
> +		goto bail_no_root;
> +	}
> +
>  	set_default_d_op(sb, &hfs_dentry_operations);
>  	res = -ENOMEM;
>  	sb->s_root = d_make_root(root_inode);

Re: [PATCH v3 RESEND] hfs: validate catalog CNIDs before instantiating inodes

[David Maximiliano Hermitte]

Hi Slava,

Thank you for the review.

Yes, I agree that the initial length validation can be simplified to:

        rec_len = fd->entrylength;
        if (rec_len <= 0 || rec_len > sizeof(rec))
                return -EIO;

I also agree that, for the fixed-size file and directory catalog records,
the checks should require the exact record size:

        rec_len != sizeof(struct hfs_cat_file)

and:

        rec_len != sizeof(struct hfs_cat_dir)

Regarding hfs_write_inode(), I intentionally left it unchanged because
the patch was trying to reject invalid CNIDs at the catalog lookup and
inode-instantiation boundaries, before a corrupted inode could reach
writeback.

However, I agree that an additional validation there may be useful as
defense in depth. Would you prefer hfs_is_valid_cnid() to be checked in
hfs_write_inode() as well, and should that check precede the existing
BUG path while otherwise leaving its behavior unchanged?

I will prepare the next revision after your guidance on that point.

Thanks,
David

Re: [PATCH v3 RESEND] hfs: validate catalog CNIDs before instantiating inodes

[Viacheslav Dubeyko]

On Tue, 2026-07-07 at 18:31 -0300, dave mad maxXx wrote:
> Hi Slava,
> Thank you for the review.
> Yes, I agree that the initial length validation can be simplified to:
> rec_len = fd->entrylength;
> if (rec_len <= 0 || rec_len > sizeof(rec))
>         return -EIO;
> 
> I also agree that, for the fixed-size file and directory catalog
> records, the checks should require the exact record size:
> rec_len != sizeof(struct hfs_cat_file)
> 
> and:
> rec_len != sizeof(struct hfs_cat_dir)
> 
> Regarding hfs_write_inode(), I intentionally left it unchanged
> because the patch was trying to reject invalid CNIDs at the catalog
> lookup and inode-instantiation boundaries, before a corrupted inode
> could reach writeback.
> However, I agree that an additional validation there may be useful as
> defense in depth. Would you prefer hfs_is_valid_cnid() to be checked
> in hfs_write_inode() as well, and should that check precede the
> existing BUG path while otherwise leaving its behavior unchanged?
> I will prepare the next revision after your guidance on that point.

Let's leave hfs_write_inode() untouched. I don't see a valid point in
this modification.

Thanks,
Slava.

Re: [PATCH v3 RESEND] hfs: validate catalog CNIDs before instantiating inodes

[Tetsuo Handa]

On 2026/07/08 6:38, David Maximiliano Hermitte wrote:
> I will prepare the next revision after your guidance on that point.

Please check sashiko's comment at
https://sashiko.dev/#/patchset/20260706095943.258065-1-davemadmaxxx%40gmail.com .