[LAU] OT: seeking help with uploading files via sftp and preventing their subsequent deletion

Ivica Ico Bukvic ico at vt.edu
Fri Oct 10 21:07:50 UTC 2014

On 10/10/2014 05:06 PM, Ivica Ico Bukvic wrote:
> On 10/10/2014 04:01 PM, Joe Hartley wrote:
>> On Fri, 10 Oct 2014 15:51:29 -0400
>> Ivica Ico Bukvic <ico at vt.edu> wrote:
>>> So, what I did so far is change /etc/ssh/sshd_config so that sftp
>>> chroots said user's home dir, and prevents access via ssh. I also
>>> created a sftponly group and added the user to it. I adjusted home dir
>>> permissions and created a subfolder "submissions" where users can 
>>> submit
>>> their projects. Finally, I added umask to strip permissions from
>>> uploaded files.
>>> So, the /etc/ssh/sshd_config has the following entry
>>> Match Group sftponly
>>> ChrootDirectory /home/%u
>>> ForceCommand internal-sftp -u 0222
>>> X11Forwarding no
>>> AllowTcpForwarding no
>> What's your subsystem line look like?  You can force the umask there 
>> with
>> the -u directive.  Example:
>> Subsystem sftp /usr/libexec/openssh/sftp-server -u 0002
>> If your sftp-server does not support -u then you can get the same effect
>> with this:
>> Subsystem sftp /bin/sh -c 'umask 0002; /usr/lib/openssh/sftp-server'
> Thanks for this but I thought that is what ForceCommand internal-sftp 
> -u 0222 does (and it does change file permissions except that even if 
> permissions are 000 I can still delete the file through sftp.
> Subsystem is
> Subsystem sftp /usr/lib/openssh/sftp-server
Also, the problem with this issue is that this needs to be specific to 
one user, not system-wide, hence my preference of ForceCommand...

Ivica Ico Bukvic, D.M.A.
Associate Professor
Computer Music
ICAT Senior Fellow
Virginia Tech
School of Performing Arts - 0141
Blacksburg, VA 24061
(540) 231-6139
ico at vt.edu

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