Re: combination of cifs and ecryptfs not working - readonly problems

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Hi,

the reason is the following:


ecryptfs_privileged_open:

https://github.com/torvalds/linux/blob/v4.19-rc4/fs/ecryptfs/kthread.c#L126

https://github.com/torvalds/linux/blob/v4.19-rc4/fs/ecryptfs/kthread.c#L147

IS_RDONLY is defined through sb_rdonly:

https://github.com/torvalds/linux/blob/v4.19-rc4/include/linux/fs.h#L1916

and the reason is:

https://github.com/torvalds/linux/blob/v4.19-rc4/include/linux/fs.h#L1906

*Exception: SB_RDONLY is always applied to the entire file system.*


Therefore i think the code should not always try to get a read/write
file and fail if this is not possible. Instead the code should open the
file read-only if an error has occured due to permissions. If this is
still not possible, the code should fail.


Best Regards

Hajo


Am 15.09.2018 um 01:10 schrieb Alex Braunegg:
> This issue sounds very similar to this one I brought up in 2014:
>
> https://www.spinics.net/lists/ecryptfs/msg00567.html 
>
> I never got to the bottom of why it was occurring - but did look at the
> kernel code at the time to see what was going on but I cannot recall what I
> found out.
>
> Best regards,
>
> Alex
>
> -----Original Message-----
> From: ecryptfs-owner@xxxxxxxxxxxxxxx [mailto:ecryptfs-owner@xxxxxxxxxxxxxxx]
> On Behalf Of Christian Kujau
> Sent: Friday, 14 September 2018 4:30 PM
> To: Hans-Joachim Kliemeck
> Cc: ecryptfs@xxxxxxxxxxxxxxx
> Subject: Re: combination of cifs and ecryptfs not working - readonly
> problems
>
> On Sun, 2 Sep 2018, Hans-Joachim Kliemeck wrote:
>> remote cifs server:
>> seems to be a proftpd with mod_sftp (with CIFS Unix Extensions), but i
> This sounds....rather exotic :-)
>
> I tried to emulate your setup with a standard Samba v4.8.2 server but 
> could not reproduce the issue:
>
> # mount | tail -2
> //sid0/test on /opt/backup/remote-encrypted type cifs
> (rw,relatime,vers=1.0,sec=none,cache=strict,domain=SID0,uid=0,noforceuid,gid
> =0,noforcegid,addr=192.168.56.130,unix,posixpaths,serverino,mapposix,acl,rsi
> ze=1048576,wsize=65536,echo_interval=60,actimeo=1)
> /opt/backup/remote-encrypted on /opt/backup/remote type ecryptfs
> (rw,relatime,ecryptfs_sig=5e0685315ad3478b,ecryptfs_cipher=aes,ecryptfs_key_
> bytes=32,ecryptfs_unlink_sigs)
>
> ...and rsync did finish w/o errors. So maybe we'd need to look at the 
> server's mod_sftp log files to see what's going on here..?
>
> Note: Hetzner appears to support many other backup mechanisms[0], 
> including BorgBackup, that may be something to look into.
>
> Christian.
>
> [0] https://wiki.hetzner.de/index.php/Backup




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