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
