linux-kernel - RE: [PATCH v3] hfs: remove BUG() from hfs_release_folio()/hfs_test_inode()/hfs_write

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Message-ID: <9a18338da59460bd5c95605d8b10f895a0b7dbb8.camel@ibm.com>
Date: Wed, 23 Jul 2025 18:43:07 +0000
From: Viacheslav Dubeyko <Slava.Dubeyko@....com>
To: "penguin-kernel@...ove.SAKURA.ne.jp" <penguin-kernel@...ove.SAKURA.ne.jp>,
        "willy@...radead.org" <willy@...radead.org>
CC: "glaubitz@...sik.fu-berlin.de" <glaubitz@...sik.fu-berlin.de>,
        "frank.li@...o.com" <frank.li@...o.com>,
        "slava@...eyko.com"
	<slava@...eyko.com>,
        "linux-fsdevel@...r.kernel.org"
	<linux-fsdevel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>,
        "akpm@...ux-foundation.org"
	<akpm@...ux-foundation.org>
Subject: RE: [PATCH v3] hfs: remove BUG() from
 hfs_release_folio()/hfs_test_inode()/hfs_write_inode()

On Wed, 2025-07-23 at 18:19 +0000, Viacheslav Dubeyko wrote:
> On Wed, 2025-07-23 at 11:16 +0900, Tetsuo Handa wrote:
> > With below change, legitimate HFS filesystem images can be mounted.
> > 
> > But is crafted HFS filesystem images can not be mounted expected result?
> > 
> >   # losetup -a
> >   /dev/loop0: [0001]:7185 (/memfd:syzkaller (deleted))
> >   # mount -t hfs /dev/loop0 /mnt/
> >   mount: /mnt: filesystem was mounted, but any subsequent operation failed: Operation not permitted.
> >   # fsck.hfs /dev/loop0
> >   ** /dev/loop0
> >      Executing fsck_hfs (version 540.1-Linux).
> >   ** Checking HFS volume.
> >      Invalid extent entry
> >   (3, 0)
> >   ** The volume   could not be verified completely.
> >   # mount -t hfs /dev/loop0 /mnt/
> >   mount: /mnt: filesystem was mounted, but any subsequent operation failed: Operation not permitted.
> > 
> > Also, are IDs which should be excluded from make_bad_inode() conditions
> > same for HFS_CDR_FIL and HFS_CDR_DIR ?
> > 
> > 
> > --- a/fs/hfs/inode.c
> > +++ b/fs/hfs/inode.c
> > @@ -358,6 +358,8 @@ static int hfs_read_inode(struct inode *inode, void *data)
> >                 inode->i_op = &hfs_file_inode_operations;
> >                 inode->i_fop = &hfs_file_operations;
> >                 inode->i_mapping->a_ops = &hfs_aops;
> > +               if (inode->i_ino < HFS_FIRSTUSER_CNID)
> > +                       goto check_reserved_ino;
> >                 break;
> >         case HFS_CDR_DIR:
> >                 inode->i_ino = be32_to_cpu(rec->dir.DirID);
> > @@ -368,6 +370,24 @@ static int hfs_read_inode(struct inode *inode, void *data)
> >                                       inode_set_atime_to_ts(inode, inode_set_ctime_to_ts(inode, hfs_m_to_utime(rec->dir.MdDat))));
> >                 inode->i_op = &hfs_dir_inode_operations;
> >                 inode->i_fop = &hfs_dir_operations;
> > +               if (inode->i_ino < HFS_FIRSTUSER_CNID)
> > +                       goto check_reserved_ino;
> > +               break;
> > +       default:
> > +               make_bad_inode(inode);
> > +       }
> > +       return 0;
> > +check_reserved_ino:
> > +       switch (inode->i_ino) {
> > +       case HFS_POR_CNID:
> > +       case HFS_ROOT_CNID:
> > +       case HFS_EXT_CNID:
> > +       case HFS_CAT_CNID:
> > +       case HFS_BAD_CNID:
> > +       case HFS_ALLOC_CNID:
> > +       case HFS_START_CNID:
> > +       case HFS_ATTR_CNID:
> > +       case HFS_EXCH_CNID:
> >                 break;
> >         default:
> >                 make_bad_inode(inode);
> 
> I have missed that this list contains [1]:
> 
> #define HFS_POR_CNID		1	/* Parent Of the Root */
> #define HFS_ROOT_CNID		2	/* ROOT directory */
> 
> Of course, hfs_read_inode() can be called for the root directory and parent of
> the root cases. So, HFS_POR_CNID and HFS_ROOT_CNID are legitimate values.
> However, the other constants cannot be used because they should be described in
> superblock (MDB) and Catalog File cannot have the records for them.
> 

I have checked the HFS specification. So, additional corrections:

#define HFS_POR_CNID		1	/* Parent Of the Root */
#define HFS_ROOT_CNID		2	/* ROOT directory */

These values are legitimate values.

#define HFS_EXT_CNID		3	/* EXTents B-tree */
#define HFS_CAT_CNID		4	/* CATalog B-tree */

This metadata structures are defined in MDB.

#define HFS_BAD_CNID		5	/* BAD blocks file */

This could be defined in Catalog File because MDB has nothing for this metadata
structure. However, it's ancient technology.

#define HFS_ALLOC_CNID		6	/* ALLOCation file (HFS+) */
#define HFS_START_CNID		7	/* STARTup file (HFS+) */
#define HFS_ATTR_CNID		8	/* ATTRibutes file (HFS+) */

These value are invalid for HFS.

#define HFS_EXCH_CNID		15	/* ExchangeFiles temp id */

This could be defined in Catalog File (maybe not). I didn't find anything
related to this in HFS specification.

> Thanks,
> Slava.
> 
> [1] https://elixir.bootlin.com/linux/v6.16-rc7/source/fs/hfs/hfs.h#L41