linux-kernel - Re: [PATCH v7 08/24] erofs: add namei functions

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Date:   Thu, 15 Aug 2019 15:25:35 +0800
From:   Gao Xiang <gaoxiang25@...wei.com>
To:     Pavel Machek <pavel@...x.de>
CC:     linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Theodore Ts'o <tytso@....edu>, David Sterba <dsterba@...e.cz>,
        Amir Goldstein <amir73il@...il.com>,
        Christoph Hellwig <hch@...radead.org>,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        Dave Chinner <david@...morbit.com>,
        "Jaegeuk Kim" <jaegeuk@...nel.org>, Jan Kara <jack@...e.cz>,
        Richard Weinberger <richard@....at>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        <devel@...verdev.osuosl.org>, <linux-erofs@...ts.ozlabs.org>,
        Chao Yu <yuchao0@...wei.com>, Miao Xie <miaoxie@...wei.com>,
        Li Guifu <bluce.liguifu@...wei.com>,
        Fang Wei <fangwei1@...wei.com>
Subject: Re: [PATCH v7 08/24] erofs: add namei functions

Hi Pavel,

On Thu, Aug 15, 2019 at 09:01:32AM +0200, Pavel Machek wrote:
> Hi!
> 
> > > > +	/*
> > > > +	 * on-disk error, let's only BUG_ON in the debugging mode.
> > > > +	 * otherwise, it will return 1 to just skip the invalid name
> > > > +	 * and go on (in consideration of the lookup performance).
> > > > +	 */
> > > > +	DBG_BUGON(qd->name > qd->end);
> > > 
> > > I believe you should check for errors in non-debug mode, too.
> > 
> > Thanks for your kindly reply!
> > 
> > The following is just my personal thought... If I am wrong, please
> > kindly point out...
> > 
> > As you can see, this is a new prefixed string binary search algorithm
> > which can provide similar performance with hashed approach (but no
> > need to store hash value at all), so I really care about its lookup
> > performance.
> > 
> > There is something needing to be concerned, is, whether namei() should
> > report any potential on-disk issues or just return -ENOENT for these
> > corrupted dirs, I think I tend to use the latter one.
> 
> -ENOENT is okay for corrupted directories, as long as corrupted
> directories do not cause some kind of security bugs (memory
> corruption, crashes, ...)

Yes, I am certain that it will return -ENOENT for such corrupted
directories and it will certainly not crash the kernel as well.

I have fuzzed it for several months and it seems fine after
commit 419d6efc50e9 ("staging: erofs: keep corrupted fs from crashing kernel in erofs_namei()")

Don't worry about that :)

Thanks,
Gao Xiang

> 
> 
> Best regards,
> 								Pavel
> -- 
> DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
> HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany