Docker container ignoring permissions?

[CS01-HS]

I created an unRAID user limited (id 1006) which I'm trying to use to limit write permission in docker containers that support PUID.

 

Can anyone explain the following behavior?

 

Launch EmbyServer shell with user nobody

# docker exec -u 99 -it EmbyServer sh

Create a file writable only by nobody

/ $ touch /media/TV/x
/ $ chmod go-w /media/TV/x
/ $ ls -l /media/TV/x
-rw-r--r--    1 99       root             0 Jan 11 11:35 /media/TV/x

 

Launch sonarr shell with user limited

# docker exec -u 1006 -it sonarr sh

Confirm I'm limited (id 1006):

$ whoami
abc
$ grep abc /etc/passwd
abc:x:1006:100::/config:/bin/false

Check permissions on the newly-created file:

(NOTE: /media/TV in EmbyServer and /tv in sonarr map to the same host path.)

$ ls -l /tv/x   
-rw-r--r-- 1 99 root 0 Jan 11 06:35 /tv/x

So the file should not be writable by current user abc - and yet:

$ rm /tv/x
$ ls -l /tv/x
ls: cannot access '/tv/x': No such file or directory

abc can delete it.

 

What's going on?

Edited January 11, 2021 by CS01-HS

[itimpi]

Have you checked the permissions on the containing directory?   I think that ‘wx’ permissions allows deleting files within the directory.

[CS01-HS]

18 minutes ago, itimpi said:

Have you checked the permissions on the containing directory?   I think that ‘wx’ permissions allows deleting files within the directory.

Thanks. A slight variation on your suggestion, I re-ran the test but with x as directory (rather than file) - same problem:

 

docker exec -u 99 -it EmbyServer sh

/ $ mkdir /media/TV/x
/ $ chmod go-wx /media/TV/x
/ $ ls -l /media/TV/ | grep 'x'
drwxr--r--    1 99       root             0 Jan 11 12:09 x

So directory x should only be writable by nobody

Let's see if that's true:

docker exec -u 1006 -it sonarr sh

$ whoami
abc
$ grep abc /etc/passwd
abc:x:1006:100::/config:/bin/false
$ ls -l /tv/ | grep x
drwxr--r-- 1 99 root      0 Jan 11 07:09 x

$ echo 'dodeedododeedo' > /tv/x/file.txt
$ ls -l /tv/x/file.txt
-rw-r--r-- 1 abc users 15 Jan 11 07:17 /tv/x/file.txt
$ 

Nope!

Edited January 11, 2021 by CS01-HS

[CS01-HS]

This is worse than I thought. 

I created a directory in the unraid console owned by root and not readable, writable or executable by anyone else:

mkdir /mnt/user/Download/TV/y
chmod go-wxr /mnt/user/Download/TV/y

drwx------ 1 root   root     20 Jan 11 18:49 y/

And apparently any user in my sonarr container (not set as privileged) can write to and delete from it freely.

This can't be intended behavior, can it?

[ken-ji]

Looks like a bug with the shfs used by Unraid.

 

[CS01-HS]

On 1/20/2021 at 10:31 AM, ken-ji said:

Looks like a bug with the shfs used by Unraid.

 

Based on your own testing or what I reported? 

Every container with root access seems like a significant security risk.

I thought this would get more interest. Am I misunderstanding?

[ken-ji]

I did some tests and filed a bug report. But seems like no one has responded so far.

[CS01-HS]

UPDATE:

I applied the fix described in @limetech's linked comment - problem solved.