[LAU] OT: seeking help with uploading files via sftp and preventing their subsequent deletion
Ivica Ico Bukvic
ico at vt.edu
Fri Oct 10 19:51:29 UTC 2014
I am in a bit of a time-bind and am wondering if anyone could help me
with this. Namely, I am trying to cobble a sftp system where conference
participants may want to upload their proposed submissions and once they
are uploaded that they are unable to delete their own or anyone else's
submission. Going with commercial solutions is not an option.
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
So, the /etc/ssh/sshd_config has the following entry
Match Group sftponly
ForceCommand internal-sftp -u 0222
So, everything works, except no matter what permissions assign via
umask, even if I change ownership manually via a different ssh user
session, sftp client can still erase the file. How is this possible? And
more importantly, how can one circumvent that? And perhaps most
importantly is there an easier way to do this?
Below are permissions of folders in question:
drwxr-xr-x 3 root USER 4096 Oct 10 15:21 .
drwxr-xr-x 36 root root 4096 Oct 7 12:16 ..
drwxr-xr-x 2 USER sftponly 4096 Oct 10 19:39 submissions
Any idea how this can be fixed?
Ivica Ico Bukvic, D.M.A.
ICAT Senior Fellow
School of Performing Arts – 0141
Blacksburg, VA 24061
ico at vt.edu
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