Re: [PATCH] erofs: move erofs out of staging
From: Chao Yu
Date: Tue Aug 20 2019 - 22:18:16 EST
On 2019/8/21 9:48, Darrick J. Wong wrote:
> 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. :) :)
Yes, I admit that I should miss a lot of fs meta type here, but that's just a
simple example here, we should not treat it as a full design.... :)
>> * .find_fs_inode_bitmap
>> * .inject_fs_inode_bitmap
> XFS has an inode bitmap? ;)
We can leave callback as NULL? ;)
> (This is why there's no generic fuzz tool; every fs is different enough
> that doing so would be sort of a mess.)
Yes, I just wonder if there is any possible we can save some redundant work.
> ((Granted, you could also look at how xfstests uses the xfs_db fuzz
> command so at least it would be systematic...))
Okay, I will check that.
>> * .find_inode_by_num
>> * .inject_inode
>> * .pack_inode
>> * .find_tree_node_by_level
> What about the name/value btrees? (Ok, I'll stop now.)
>> 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
>>> 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 and Hydra work. (Hydra is about to be published at SOSP 19,
>>> and was partially funded from a Google Faculty Research Work.)
>>>  https://taesoo.kim/pubs/2019/xu:janus.pdf
>>>  https://github.com/sslab-gatech/janus
>>>  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.