15.09.2017 15:35, Austin S. Hemmelgarn пишет: > On 2017-09-14 23:45, Andrei Borzenkov wrote: >> 14.09.2017 18:32, Hugo Mills пишет: >>> On Thu, Sep 14, 2017 at 04:57:39PM +0200, Ulli Horlacher wrote: >>>> I use encfs on top of btrfs. >>>> I can create btrfs snapshots, but I have no suggestive access to the >>>> files >>>> in these snaspshots, because they look like: >>>> >>>> drwx------ framstag users - 2017-09-08 11:47:18 >>>> uHjprldmxo3-nSfLmcH54HMW >>>> drwxr-xr-x framstag users - 2017-09-08 11:47:18 >>>> wNEWaDCgyXTj0d-Myk8wXZfh >>>> -rw-r--r-- framstag users 377 2015-06-12 14:02:53 >>>> -zDmc7xfobKDkbl8z7oKOHxv >>>> -rw-r--r-- framstag users 2,367 2012-07-10 14:32:30 >>>> 7pfKs27K9k5zANE4WOQEuFa2 >>>> -rw------- framstag users 692 2009-10-20 13:45:41 >>>> 8SQElYCph85kDdcFasUHybVr >>>> -rw------- framstag users 2,872 2017-08-31 16:21:52 >>>> bm,yNi1e4fsAClDv7lNxxSfJ >>>> lrwxrwxrwx framstag users - 2017-06-01 15:53:00 >>>> GZxNYI0Gy96R18fz40f7k5rl -> >>>> wvuQKHYzdFbar18fW6jjOerXk2IsS4OAA2fnHalBZjMQ,7Kw0j-zE3IJqxhmmGBN8G9 >>>> -rw-r--r-- framstag users 182 2016-12-01 13:34:31 >>>> rqtNBbiYDym0hPMbBL-VLJZcFZu6nkNxlsjTX-sU88I4I1 >>>> >>>> I have to mount the snapshot with encfs, to have access to the >>>> (decrypted) >>>> files. >>>> >>>> Any better ideas? >>> >>> I'd say it's doing exactly what it should be doing. You're making a >>> copy of an encrypted data store, >> >> With all respect - snapshot is not a copy. > From a userspace perspective, it is, and that's what matters since EncFS > is a userspace tool. In fact, part of the point of a snapshot is that > it's functionally indistinguishable from a direct copy of the data > unless you start looking at block layouts (which nothing in userspace > that isn't an administration tool should be doing). >> >>> and the result is encrypted. In order >>> to read it, it needs to have the decrpytion layer applied to it with >>> the correct key (which is the need to mount the snapshot with encfs). >>> >> >> But snapshot *is* mounted implicitly as it is part of mounted btrfs >> filesystem. So I can see that this behavior could be rather unexpected. >> >>> Would you _really_ want a system where the encrypted contents of a >>> subvolume can be decrypted by simply snapshotting it? >> >> The actual question is - do you need to mount each individual btrfs >> subvolume when using encfs? If yes, this behavior is at least >> consistent. If not - how are snapshots different? > I think you're not understanding the layering here. EncFS is a FUSE > filesystem that is run as a separate layer on top of another filesystem. > It is completely agnostic of the underlying data storage > implementation, provided that said data storage enforces POSIX I/O > semantics. >
I did understand layering but I was not familiar with subtleties. I now tested encfs with subvolumes and subvolumes, present in encrypted directory, are not visible in unencrypted directory at all (and of course I cannot create subvolume on overlay mount). But - if I know encrypted name I can create subvolume with the same name - and it becomes visible under cleartext mount: bor@10:~> /usr/sbin/btrfs sub cre .encfs/CxRowQNCTNP3Bm0DlEFADnj5 Create subvolume '.encfs/CxRowQNCTNP3Bm0DlEFADnj5' bor@10:~> ll .encfs/ total 0 drwxr-xr-x 1 bor users 0 Sep 15 20:18 CxRowQNCTNP3Bm0DlEFADnj5 drwxr-xr-x 1 bor users 0 Sep 15 20:11 sub2 bor@10:~> encfs ~/.encfs ~/encfs EncFS Password: bor@10:~> ll encfs/ total 0 drwxr-xr-x 1 bor users 0 Sep 15 20:18 sub1 bor@10:~> mkdir encfs/sub1/even-deeper bor@10:~> ll .encfs/ total 0 drwxr-xr-x 1 bor users 48 Sep 15 20:19 CxRowQNCTNP3Bm0DlEFADnj5 drwxr-xr-x 1 bor users 0 Sep 15 20:11 sub2 bor@10:~> ll .encfs/CxRowQNCTNP3Bm0DlEFADnj5/ total 0 drwxr-xr-x 1 bor users 0 Sep 15 20:19 Z4yelS9xOwbOxZ0tGxopma8K bor@10:~> That is what I meant - subvolumes themselves are transparent as long as you can traverse them. So if they remain under the encfs mount root and have names that encfs can decode, it is possible to reach them. > To clarify, the procedure for mounting an EncFS volume is: > 1. Mount the underlying filesystem (usually done at boot by the init > system). > 2. Mount the EncFS instance that is using that underlying filesystem as > storage (usually done on user log-in by the session manager or PAM). > > On BTRFS, step 1 is implicit if it's a subvolume, but step 2 is never > implicit, regardless of the filesystem. Hugo's mention of needing > mounting the snapshot with EncFS refers to the second step here, not the > first. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
