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Date:   Tue, 20 Aug 2019 18:48:18 -0700
From:   "Darrick J. Wong" <darrick.wong@oracle.com>
To:     Chao Yu <yuchao0@huawei.com>
Cc:     "Theodore Y. Ts'o" <tytso@mit.edu>,
        Qu Wenruo <quwenruo.btrfs@gmx.com>,
        Gao Xiang <hsiangkao@aol.com>,
        Christoph Hellwig <hch@infradead.org>,
        Eric Biggers <ebiggers@kernel.org>,
        Richard Weinberger <richard@nod.at>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jan Kara <jack@suse.cz>, Dave Chinner <david@fromorbit.com>,
        David Sterba <dsterba@suse.cz>, Miao Xie <miaoxie@huawei.com>,
        devel <devel@driverdev.osuosl.org>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        Amir Goldstein <amir73il@gmail.com>,
        linux-erofs <linux-erofs@lists.ozlabs.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Jaegeuk Kim <jaegeuk@kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Li Guifu <bluce.liguifu@huawei.com>,
        Fang Wei <fangwei1@huawei.com>, Pavel Machek <pavel@denx.de>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH] erofs: move erofs out of staging
Message-ID: <20190821014818.GB1037422@magnolia>
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On Wed, Aug 21, 2019 at 09:34:02AM +0800, Chao Yu wrote:
> On 2019/8/20 23:56, Theodore Y. Ts'o wrote:
> > The reason why there needs to be at least some file system specific
> > code for fuzz testing is because for efficiency's sake, you don't want
> > to fuzz every single bit in the file system, but just the ones which
> > are most interesting (e.g., the metadata blocks).  For file systems
> > which use checksum to protect against accidental corruption, the file
> > system fuzzer needs to also fix up the checksums (since you can be
> > sure malicious attackers will do this).
> 
> Yup, IMO, if we really want such tool, it needs to:
> - move all generic fuzz codes (trigger random fuzzing in meta/data area) into
> that tool, and
> - make filesystem generic fs_meta/file_node lookup/inject/pack function as a
> callback, such as
>  * .find_fs_sb
>  * .inject_fs_sb
>  * .pack_fs_sb

What about group descriptors?  AG headers?  The AGFLWTFBBQLOL?

>  * .find_fs_bitmap
>  * .inject_fs_bitmap

Probably want an find/inject for log blocks too.

Oh, wait, XFS doesn't log blocks like jbd2 does. :) :)

>  * .find_fs_inode_bitmap
>  * .inject_fs_inode_bitmap

XFS has an inode bitmap? ;)

(This is why there's no generic fuzz tool; every fs is different enough
that doing so would be sort of a mess.)

((Granted, you could also look at how xfstests uses the xfs_db fuzz
command so at least it would be systematic...))

>  * .find_inode_by_num
>  * .inject_inode
>  * .pack_inode
>  * .find_tree_node_by_level
> ...

What about the name/value btrees?  (Ok, I'll stop now.)

--D

> then specific filesystem can fill the callback to tell how the tool can locate a
> field in inode or a metadata in tree node and then trigger the designed fuzz.
> 
> It will be easier to rewrite whole generic fwk for each filesystem, because
> existed filesystem userspace tool should has included above callback's detail
> codes...
> 
> > On Tue, Aug 20, 2019 at 10:24:11AM +0800, Chao Yu wrote:
> >> filesystem fill the tool's callback to seek a node/block and supported fields
> >> can be fuzzed in inode.
> 
> > 
> > What you *can* do is to make the file system specific portion of the
> > work as small as possible.  Great work in this area is Professor Kim's
> > Janus[1][2] and Hydra[2] work.  (Hydra is about to be published at SOSP 19,
> > and was partially funded from a Google Faculty Research Work.)
> > 
> > [1] https://taesoo.kim/pubs/2019/xu:janus.pdf
> > [2] https://github.com/sslab-gatech/janus
> > [3] https://github.com/sslab-gatech/hydra
> 
> Thanks for the information!
> 
> It looks like janus and hydra alreay have generic compress/decompress function
> across different filesystems, it's really a good job, I do think it may be the
> one once it becomes more generic.
> 
> Thanks
> 
> >