Thanks for the very detailed explanation dave. On Fri, Dec 14, 2012 at 10:27:16AM +1100, Dave Chinner wrote: > On Thu, Dec 13, 2012 at 12:58:40PM -0200, Carlos Maiolino wrote: > > Hi guys, > > > > I just read this blog post: > > http://crypto.junod.info/2012/12/13/hash-dos-and-btrfs/ > > > > The above describes a directory name hashing attack, where duplicate > hashes prevent creation of otherwise unique filenames in the same > directory. This problem is unique to btrfs, and has nothing to do > with the use of CRC32 for hashing - the problem is simply that btrfs > does not handle hash collisions at all well. > > FWIW, the directory name hashing tricks for fast random lookups that > btrfs uses was actually copied from XFS. XFS doesn't have this DOS > problem, however, because XFS does not use the hashed value as a > unique identifier. i.e. we can have multiple entries in a directory > that hash to exactly the same value and not have any problems at > all. > > Like I said, a problem unique to btrfs. > > > And got worried if this would not be possible with XFS after the checksum > > implementation. > > TBH I'm horrible with crypto and those maths, but I'm worried if after crc32 > > checksum implementation we may not be enabling hash-dos attacks to XFS. > > We'll be using CRCs completely internally to XFS and they are not > used as indexes into structures or lookup keys. They are purely for > verification, and hence I think it's impossible to use them as a DOS > vector... > > Cheers, > > Dave. > -- > Dave Chinner > david@xxxxxxxxxxxxx > > _______________________________________________ > xfs mailing list > xfs@xxxxxxxxxxx > http://oss.sgi.com/mailman/listinfo/xfs -- Carlos _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
