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Denial-of-Service Attack Found In Btrfs File-System
An anonymous reader writes "It's been found that the Btrfs file-system is vulnerable to a Hash-DOS attack, a denial-of-service attack caused by hash collisions within the file-system. Two DOS attack vectors were uncovered by Pascal Junod that he described as causing astonishing and unexpected success. It's hoped that the security vulnerability will be fixed for the next Linux kernel release." The article points out that these exploits require local access.
ZFS on FreeBSD or FreeNAS is great. Easily saturates gigE with a simple mirror of recent 7200rpm disks. It scales up from there, and FreeBSD is pretty rock solid.
NTFS doesn't have snapshots. Instead it relies on volume shadow copies, with known severe performance artifacts caused by needing to move snapshotted data out of the way when new writes come in. Btrfs, like ZFS and Netapp's WAFL, use a far more efficient copy-on-write strategy that avoids the write penalty. The takeaway: I would not go so far as to claim Microsoft has an enterprise-worthy solution either. If you want something with industrial strength dedup, snapshots and fault tolerance, you won't be getting it from Micorosft.
When all you have is a hammer, every problem starts to look like a thumb.
Sort of, but at least you can recover from those attacks by restarting or booting from an external source to clean up your filesystem. The second attack here leaves you with undeletable files because the file system code responsible for deleting cannot handle the multiple hash collisions. There is no way to recover from that until a patch is pushed out that fixes the problem.
ZFS on Linux does exist as a kernel module that is pretty stable and works well. http://zfsonlinux.org/ -- it was put out by Lawrence Livermore National Lab, but can't be included with the kernel distros due to GPL / CDDL license compatability issues.
VSS is the snapshot solution for NTFS, and of course it uses copy-on-write
Well. Maybe you better sit down in a comfortable chair and think about this a bit. From Microsoft's site: When a change to the original volume occurs, but before it is written to disk, the block about to be modified is read and then written to a “differences area”, which preserves a copy of the data block before it is overwritten with the change.
Think about what this means. It is not a "copy-on-write", it is a "copy-before-write". Gross abuse of terminology if anybody tries to call it a "copy-on-write", which has the very specific meaning of "don't modify the destination data". Instead, copy it, then modify the copy. OK, are we clear? VSS does not do copy-on-write, it does copy-before-write.
Now let's think about the implications of that. First, the write needs to be blocked until the copy-before-write completes, otherwise the copied data is not sure to be on stable storage. The copy-before-write needs to read the data from its original position, write it to some save area, then update some metadata to remember which data was saved where. How many disk seeks is that, if it's a spinning disk? If the save area is on the same spinning disk? If it's flash, how much write multiplication is that? When all of that is finally done, the original write can be unblocked and allowed to proceed. In total, how much slower is that than a simple, linear write? If you said "on the order of an order of magnitude" you would be in the ballpark. In face, it can get way worse than that if you are unlucky. In the best imaginable case, your write performance is going to take a hit by a factor of three. Usually, much much worse.
OK, did we get this straight? As a final exercise, see if you can figure out who was talking nonsense.
When all you have is a hammer, every problem starts to look like a thumb.