On 6/12/23 18:19, Eric Biggers wrote: > This is the first time you've received an email from this sender > ebiggers@xxxxxxxxxx, please exercise caution when clicking on links or opening > attachments. > > > On Mon, Jun 12, 2023 at 03:52:17PM +0200, Sergei Shtepa wrote: > > Hi all. > > > > I am happy to offer a improved version of the Block Devices Snapshots > > Module. It allows to create non-persistent snapshots of any block devices. > > The main purpose of such snapshots is to provide backups of block devices. > > See more in Documentation/block/blksnap.rst. > > How does blksnap interact with blk-crypto? > > I.e., what happens if a bio with a ->bi_crypt_context set is submitted to a > block device that has blksnap active? > > If you are unfamiliar with blk-crypto, please read > Documentation/block/inline-encryption.rst Thank you, this is an important point. Yes, that's right. The current version of blksnap can cause blk-crypto to malfunction while holding a snapshot. When handling bios from the file system, the ->bi_crypt_context is preserved. But the bio requests serving the snapshot are executed without context. I think that the snapshot will be unreadable. But I don't see any obstacles in the way of blksnap and blk-crypto compatibility. If DM implements support for blk-crypto, then the same principle can be applied for blksnap. I think that the integration of blksnap with blk-crypto may be one of the stages of further development. The dm-crypto should work properly. It is noteworthy that in 7 years of using the out-of-tree module to take a snapshot, I have not encountered cases of such problems. But incompatibility with blk-crypto is possible, this is already a pain for some users. I will request this information from our support team. > > It looks like blksnap hooks into the block layer directly, via the new > "blkfilter" mechanism. I'm concerned that it might ignore ->bi_crypt_context > and write data to the disk in plaintext, when it is supposed to be encrypted. No. The "blkfilter" mechanism should not affect the operation of blk-crypto. It does not change the bio. Only a module that has been attached and provides its own filtering algorithm, such as blksnap, can violate the logic of blk-crypto. Therefore, until the blksnap module is loaded, blk-crypto should work as before.
