linux-kernel - RE: [PATCH v2 2/2] hfs: Update sanity check of the root record

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <74eae0401c7a518d1593cce875a402c0a9ded360.camel@ibm.com>
Date: Mon, 10 Nov 2025 23:34:39 +0000
From: Viacheslav Dubeyko <Slava.Dubeyko@....com>
To: "contact@...rnon.com" <contact@...rnon.com>
CC: "frank.li@...o.com" <frank.li@...o.com>,
        "linux-kernel-mentees@...ts.linux.dev"
	<linux-kernel-mentees@...ts.linux.dev>,
        "slava@...eyko.com"
	<slava@...eyko.com>,
        "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>,
        "penguin-kernel@...ove.sakura.ne.jp"
	<penguin-kernel@...ove.sakura.ne.jp>,
        "syzbot+97e301b4b82ae803d21b@...kaller.appspotmail.com"
	<syzbot+97e301b4b82ae803d21b@...kaller.appspotmail.com>,
        "skhan@...uxfoundation.org" <skhan@...uxfoundation.org>,
        "glaubitz@...sik.fu-berlin.de" <glaubitz@...sik.fu-berlin.de>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: RE: [PATCH v2 2/2] hfs: Update sanity check of the root record

On Mon, 2025-11-10 at 23:03 +0000, George Anthony Vernon wrote:
> On Tue, Nov 04, 2025 at 11:01:31PM +0000, Viacheslav Dubeyko wrote:
> > On Tue, 2025-11-04 at 01:47 +0000, George Anthony Vernon wrote:
> > > syzbot is reporting that BUG() in hfs_write_inode() fires upon unmount
> > > operation when the inode number of the record retrieved as a result of
> > > hfs_cat_find_brec(HFS_ROOT_CNID) is not HFS_ROOT_CNID, for commit
> > > b905bafdea21 ("hfs: Sanity check the root record") checked the record
> > > size and the record type but did not check the inode number.
> > > 
> > > Reported-by: syzbot+97e301b4b82ae803d21b@...kaller.appspotmail.com
> > > Closes: https://syzkaller.appspot.com/bug?extid=97e301b4b82ae803d21b    
> > > Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
> > > Signed-off-by: George Anthony Vernon <contact@...rnon.com>
> > > ---
> > >  fs/hfs/super.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/fs/hfs/super.c b/fs/hfs/super.c
> > > index 47f50fa555a4..a7dd20f2d743 100644
> > > --- a/fs/hfs/super.c
> > > +++ b/fs/hfs/super.c
> > > @@ -358,7 +358,7 @@ static int hfs_fill_super(struct super_block *sb, struct fs_context *fc)
> > >  			goto bail_hfs_find;
> > >  		}
> > >  		hfs_bnode_read(fd.bnode, &rec, fd.entryoffset, fd.entrylength);
> > > -		if (rec.type != HFS_CDR_DIR)
> > > +		if (rec.type != HFS_CDR_DIR || rec.dir.DirID != cpu_to_be32(HFS_ROOT_CNID))
> > 
> > This check is completely unnecessary. Because, we have hfs_iget() then [1]:
> > 
> > The hfs_iget() calls iget5_locked() [2]:
> > 
> > And iget5_locked() calls hfs_read_inode(). And hfs_read_inode() will call
> > is_valid_cnid() after applying your patch. So, is_valid_cnid() in
> > hfs_read_inode() can completely manage the issue. This is why we don't need in
> > this modification after your first patch.
> > 
> 
> I think Tetsuo's concern is that a directory catalog record with
> cnid > 15 might be returned as a result of hfs_bnode_read, which
> is_valid_cnid() would not protect against. I've satisfied myself that
> hfs_bnode_read() in hfs_fill_super() will populate hfs_find_data fd
> correctly and crash out if it failed to find a record with root CNID so
> this path is unreachable and there is no need for the second patch.
> 

Technically speaking, we can adopt this check to be completely sure that nothing
will be wrong during the mount operation. But I believe that is_valid_cnid()
should be good enough to manage this. Potential argument could be that the check
of rec.dir.DirID could be faster operation than to call hfs_iget(). But mount is
rare and not very fast operation, anyway. And if we fail to mount, then the
speed of mount operation is not very important.

> > But I think we need to check that root_inode is not bad inode afterwards:
> > 
> > 	root_inode = hfs_iget(sb, &fd.search_key->cat, &rec);
> > 	hfs_find_exit(&fd);
> > 	if (!root_inode || is_bad_inode(root_inode))
> > 		goto bail_no_root;
> 
> Agreed, I see hfs_read_inode might return a bad inode. Thanks for
> catching this. I noticed also that it returns an int but the return
> value holds no meaning; it is always zero.
> 
> 

I've realized that hfs_write_inode() doesn't check that inode is bad like other
file systems do. Probably, we need to have this check too.

Thanks,
Slava.