this post was submitted on 04 Apr 2024
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sshfs pemission denied on root path folder (lemmy.ml)
submitted 7 months ago* (last edited 7 months ago) by [email protected] to c/[email protected]
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Hello !

Getting a bit annoyed with permission issues with samba and sshfs. If someone could give me some input on how to find an other more elegant and secure way to share a folder path owned by root, I would really appreciate it !

Context

  • The following folder path is owned by root (docker volume):

/var/lib/docker/volumes/syncthing_data/_data/folder

  • The child folders are owned by the user server

/var/lib/docker/volumes/syncthing_data/_data/folder

  • The user server is in the sudoers file
  • Server is in the docker groupe
  • fuse.confhas the user_allow_other uncommented

Mount point with sshfs

sudo sshfs [email protected]:/var/lib/docker/volumes/syncthing_data/_data/folder /home/user/folder -o allow_other

Permission denied

Things I tried

  • Adding other options like gid 0,27,1000 uid 0,27,1000 default_permissions...
  • Finding my way through stackoverflow, unix.stackexchange...

Solution I found

  1. Making a bind mount from the root owned path to a new path owned by server

sudo mount --bind /var/lib/docker/volumes/syncthing_data/_data/folder /home/server/folder

  1. Mount point with sshfs

sshfs [email protected]:/home/server/folder /home/user/folder

Question

While the above solution works, It overcomplicates my setup and adds an unecessary mount point to my laptop and fstab.

Isn't there a more elegant solution to work directly with the user server (which has root access) to mount the folder with sshfs directly even if the folder path is owned by root?

I mean the user has root access so something like:

sshfs [email protected]:/home/server/folder /home/user/folder -o allow_other should work even if the first part of the path is owned by root.

Changing owner/permission of the path recursively is out of question !

Thank you for your insights !

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[–] [email protected] 2 points 7 months ago* (last edited 7 months ago) (1 children)

Heyha !

Thanks for your input, you pointed the right direction ! After some more reading, this is what I found.

Adding the following line in sudoers file after @includedir /etc/sudoers.d:

server ALL = NOPASSWD: /usr/lib/openssh/sftp-server

Works without the need of a sudo session for the sftp-server. I have no idea if this is good security practice but If i had to guess I would say no. Having the NOPASSWD argument for something critical as an ftp server seems... Not a good idea ! But I'm not an expert, so I'm just guessing :/.

If I may, how would you tackle such an use case ? My first solution seems way more secure with the right permissions on the bind mount, what do you think ?

Thanks for your nice tip to right direction :D !

[–] [email protected] 1 points 7 months ago* (last edited 7 months ago) (1 children)

As far as I understand, the user server is not the user running your web server e.g. www-data, right? Otherwise I would advise against giving him elevated privileges such as sudo rights.

If the authentication of the user server has sufficiently high level, e.g. a strong password, SSH key authentication, I don't see a high risk in using the NOPASSWD method. But, as I am no expert, please take this with a grain of salt.

[–] [email protected] 1 points 7 months ago (1 children)

Sorry for the late response !

As far as I understand, the user server is not the user running your web server e.g. www-data, right?

Are you sure about that? I mean, in the sudoers file I added the user server with NOPASSWD and not www-data for the specific service. And it works that way.

Maybe I misunderstand something here, if so please correct me. Is there anyway I could check this out? Do I need to check the owner on my host or my client trying to mount the path?

Thank you !!

[–] [email protected] 1 points 7 months ago

By the 'user running the web server' I mean the user running the Apache, Ngix or whatever web server on your system. Usually, afaIk, you should not be able to login as e.g. www-data on the system. You can identify the username by running ps -ef and searching for the web server process. You'll find the corresponding user name in the first column.