Re: lnk_file read permission

[Gionatan Danti <g.danti@assyoma.it>]

Il 2020-07-31 19:09 Gionatan Danti ha scritto:
> I did not know that systemd would, with specific settings, create a
> private mysql data dir.
> I would try the var_lib_t approach more widely.
> Thanks.

Mmm, it seems labeling the link as var_lib_t is not always sufficient.
Doing a mongodb test relocation from /var/lib/mongodb to /zzz/mongodb 
the service does not start, even if I can see the link having var_lib_t 
label:

# ls -alZ /var/lib/
...
lrwxrwxrwx. root    root    unconfined_u:object_r:var_lib_t:s0 mongodb 
-> /zzz/mongodb

Indeed, I can see the following in /var/log/audit:

type=AVC msg=audit(1596222151.576:253): avc:  denied  { read } for  
pid=4313 comm="mongod" name="mongodb" dev="dm-0" ino=33673444 
scontext=system_u:system_r:mongod_t:s0 
tcontext=unconfined_u:object_r:var_lib_t:s0 tclass=lnk_file permissive=0

Relabeling the synlink with its "native" label via restorecon -RF 
produce the following:

# ls -alZ /var/lib/
...
lrwxrwxrwx. root    root    system_u:object_r:mongod_var_lib_t:s0 
mongodb -> /zzz/mongodb

But the service again does not start, with the followin logs:

type=AVC msg=audit(1596222240.363:257): avc:  denied  { read } for  
pid=4344 comm="mongod" name="mongodb" dev="dm-0" ino=33673444 
scontext=system_u:system_r:mongod_t:s0 
tcontext=system_u:object_r:mongod_var_lib_t:s0 tclass=lnk_file 
permissive=0

What would be the best approach in this case? I know that one approach 
would be to use a bind mount, but I would like to avoid it because:
a) it has bad filesystem discoverably (you had to search for bind mount 
explicitly, while a symlink is visible even with a simple ls)
b) I need to setup a fcontext <<None>> for the actual dir which is 
bind-mounted (otherwise, a "restorecon -RF /zzz/" will cause issues, by 
relabeling any files with default_t)

I am open to suggestions...
Thanks.

-- 
Danti Gionatan
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