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 > > >
