[...] >>> I have made a simple fuzzer to inject messy in inode metadata, >>> dir data, compressed indexes and super block, >>> https://git.kernel.org/pub/scm/linux/kernel/git/xiang/erofs-utils.git/commit/?h=experimental-fuzzer >>> >>> I am testing with some given dirs and the following script. >>> Does it look reasonable? >>> >>> # !/bin/bash >>> >>> mkdir -p mntdir >>> >>> for ((i=0; i<1000; ++i)); do >>> mkfs/mkfs.erofs -F$i testdir_fsl.fuzz.img testdir_fsl > /dev/null 2>&1 >> >> mkfs fuzzes the image? Er.... > > Thanks for your reply. > > First, This is just the first step of erofs fuzzer I wrote yesterday night... > >> >> Over in XFS land we have an xfs debugging tool (xfs_db) that knows how >> to dump (and write!) most every field of every metadata type. This >> makes it fairly easy to write systematic level 0 fuzzing tests that >> check how well the filesystem reacts to garbage data (zeroing, >> randomizing, oneing, adding and subtracting small integers) in a field. >> (It also knows how to trash entire blocks.) The same tool exists for btrfs, although lacks the write ability, but that dump is more comprehensive and a great tool to learn the on-disk format. And for the fuzzing defending part, just a few kernel releases ago, there is none for btrfs, and now we have a full static verification layer to cover (almost) all on-disk data at read and write time. (Along with enhanced runtime check) We have covered from vague values inside tree blocks and invalid/missing cross-ref find at runtime. Currently the two layered check works pretty fine (well, sometimes too good to detect older, improper behaved kernel). - Tree blocks with vague data just get rejected by verification layer So that all members should fit on-disk format, from alignment to generation to inode mode. The error will trigger a good enough (TM) error message for developer to read, and if we have other copies, we retry other copies just as we hit a bad copy. - At runtime, we have much less to check Only cross-ref related things can be wrong now. since everything inside a single tree block has already be checked. In fact, from my respect of view, such read time check should be there from the very beginning. It acts kinda of a on-disk format spec. (In fact, by implementing the verification layer itself, it already exposes a lot of btrfs design trade-offs) Even for a fs as complex (buggy) as btrfs, we only take 1K lines to implement the verification layer. So I'd like to see every new mainlined fs to have such ability. > > Actually, compared with XFS, EROFS has rather simple on-disk format. > What we inject one time is quite deterministic. > > The first step just purposely writes some random fuzzed data to > the base inode metadata, compressed indexes, or dir data field > (one round one field) to make it validity and coverability. > >> >> You might want to write such a debugging tool for erofs so that you can >> take apart crashed images to get a better idea of what went wrong, and >> to write easy fuzzing tests. > > Yes, we will do such a debugging tool of course. Actually Li Guifu is now > developping a erofs-fuse to support old linux versions or other OSes for > archiveing only use, we will base on that code to develop a better fuzzer > tool as well. Personally speaking, debugging tool is way more important than a running kernel module/fuse. It's human trying to write the code, most of time is spent educating code readers, thus debugging tool is way more important than dead cold code. Thanks, Qu > > Thanks, > Gao Xiang > >> >> --D >> >>> umount mntdir >>> mount -t erofs -o loop testdir_fsl.fuzz.img mntdir >>> for j in `find mntdir -type f`; do >>> md5sum $j > /dev/null >>> done >>> done >>> >>> Thanks, >>> Gao Xiang >>> >>>> >>>> Thanks, >>>> Gao Xiang >>>>
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