linux-kernel - Re: [PATCH] staging: erofs: harden inode lookup for 32-bit platforms

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Message-ID: <20181011111204.zhxh5tw66pdxb3zh@mwanda>
Date:   Thu, 11 Oct 2018 14:12:04 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Gao Xiang <gaoxiang25@...wei.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        devel@...verdev.osuosl.org, linux-erofs@...ts.ozlabs.org,
        Chao Yu <yuchao0@...wei.com>,
        LKML <linux-kernel@...r.kernel.org>, weidu.du@...wei.com,
        Miao Xie <miaoxie@...wei.com>
Subject: Re: [PATCH] staging: erofs: harden inode lookup for 32-bit platforms

On Thu, Oct 11, 2018 at 06:49:57PM +0800, Gao Xiang wrote:
> Hi Dan,
> 
> On 2018/10/11 18:18, Dan Carpenter wrote:
> > On Thu, Oct 11, 2018 at 05:46:26PM +0800, Gao Xiang wrote:
> >>
> >>
> >> On 2018/10/11 16:44, Dan Carpenter wrote:
> >>> On Tue, Oct 09, 2018 at 10:07:13PM +0800, Gao Xiang wrote:
> >>>> This patch introduces inode hash function, test and set callbacks,
> >>>> and iget5_locked to find the right inode for 32-bit platforms.
> >>>>
> >>>
> >>> The way I read this changelog, we're trying to deal with corrupt file
> >>> systems?  Is that correct?  Presumably in the current code it could lead
> >>> to a Oops or something?
> >>
> >> No, this commit isn't trying to deal with corrupt file systems.
> >> In EROFS, the nid is not continuous and it represents the inode offset
> >> inode offset = nid * 32.
> >> Therefore the nid is 64-bit both for 32-bit and 64-bit platforms. However,
> >> i_ino is 'unsigned long', which means for 32-bit platforms, i_ino is not enough
> >> to contain the nid.
> >>
> >> Therefore, we should use iget5_locked for this case.
> > 
> > I guess what I'm saying is, what are the user visible effects of this
> > patch?  It's hard for me to tell from the patch description.  Could you
> > please re-write the description and send a v2?
> 
> Sorry for my just hurry reply. It seems I really misunderstood your point :-(
> 
> If all nids are less than 32-bit, the user will see the correct inode/nid number
> for all 32-bit platforms, but if some nids are greater than 32-bit, it could be
> collisions without this patch for 32-bit platforms.
> 
> This patch switch the inode number by XOR the high 32-bit and the low 32-bit,
> use customized tester to avoid collisions for 32-bit platforms.
> 
> I will send v2 to fix the commit message...but it seems Greg is already merged in
> https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging.git/commit/?h=staging-testing&id=2abd7814138774eb56319e9dcc0abd08ece45424
> 

Oh.  Then that's fine then.  If Greg already merged it, then it's too
late to change.  Thanks for the explanation, though.

regards,
dan carpenter