linux-kernel - RE: [PATCH v4] hfs: update sanity check of the root record

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Message-ID: <a3d1464ee40df7f072ea1c19e1ccf533e34554ca.camel@ibm.com>
Date: Mon, 4 Aug 2025 22:00:43 +0000
From: Viacheslav Dubeyko <Slava.Dubeyko@....com>
To: "leocstone@...il.com" <leocstone@...il.com>,
        "jack@...e.cz"
	<jack@...e.cz>,
        "penguin-kernel@...ove.SAKURA.ne.jp"
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        "brauner@...nel.org" <brauner@...nel.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"
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	<akpm@...ux-foundation.org>,
        "viro@...iv.linux.org.uk"
	<viro@...iv.linux.org.uk>
Subject: RE: [PATCH v4] hfs: update sanity check of the root record

On Sat, 2025-08-02 at 06:52 +0900, Tetsuo Handa wrote:
> On 2025/08/02 3:26, Viacheslav Dubeyko wrote:
> > On Fri, 2025-08-01 at 06:12 +0900, Tetsuo Handa wrote:
> > > On 2025/08/01 3:03, Viacheslav Dubeyko wrote:
> > > > On Thu, 2025-07-31 at 07:02 +0900, Tetsuo Handa wrote:
> > > > > On 2025/07/31 4:24, Viacheslav Dubeyko wrote:
> > > > > > If we considering case HFS_CDR_DIR in hfs_read_inode(), then we know that it
> > > > > > could be HFS_POR_CNID, HFS_ROOT_CNID, or >= HFS_FIRSTUSER_CNID. Do you mean that
> > > > > > HFS_POR_CNID could be a problem in hfs_write_inode()?
> > > > > 
> > > > > Yes. Passing one of 1, 5 or 15 instead of 2 from hfs_fill_super() triggers BUG()
> > > > > in hfs_write_inode(). We *MUST* validate at hfs_fill_super(), or hfs_read_inode()
> > > > > shall have to also reject 1, 5 and 15 (and as a result only accept 2).
> > > > 
> > > > The fix should be in hfs_read_inode(). Currently, suggested solution hides the
> > > > issue but not fix the problem.
> > > 
> > > Not fixing this problem might be hiding other issues, by hitting BUG() before
> > > other issues shows up.
> > > 
> > 
> > I am not going to start a philosophical discussion. We simply need to fix the
> > bug. The suggested patch doesn't fix the issue.
> 
> What is your issue?
> 
> My issue (what syzbot is reporting) is that the kernel crashes if the inode number
> of the record retrieved as a result of hfs_cat_find_brec(HFS_ROOT_CNID) is not
> HFS_ROOT_CNID. My suggested patch does fix my issue.
> 
> > Please, don't use hardcoded value. I already shared the point that we must use
> > the declared constants.
> > 
> > This function is incorrect and it cannot work for folders and files at the same
> > time.
> 
> I already shared that I don't plan to try writing such function
> ( http://lkml.kernel.org/r/38d8f48e-47c3-4d67-9caa-498f3b47004f@I-love.SAKURA.ne.jp   ).
> 
> Please show us your patch that solves your issue.

OK. It will be faster to write my own patch. It works for me.

Thanks,
Slava.