Dear list,
I am writing this email as suggested here:
https://lists.fedoraproject.org/archives/list/selinux@xxxxxxxxxxxxxxxxxxxxxxx/message/GWEWGDUQS6PERAYEJHL2EE4GDO432IAO/
To recap: I have issue with selinux permission when relocating specific
daemon data directory, and using symlink in the original location. For
example, lets consider moving /var/lib/mysql in a new, bigger volume.
After moving /var/lib/mysql in /data/lib/mysql and creating a symlink
for the new location, I used semanage fcontext to add the relative
equivalency rules. Moreover, I changed my.cnf to explicitly point to the
new data dir and socket file. So far, so good.
When restarting apache, I noticed it can't connect to mysql. ausearch -m
avc showed the following:
...
type=AVC msg=audit(1596055762.070:175569): avc: denied { read } for
pid=72946 comm="httpd" name="mysql" dev="sda2" ino=103
scontext=system_u:system_r:httpd_t:s0
tcontext=system_u:object_r:mysqld_db_t:s0 tclass=lnk_file permissive=0
The log above clearly states that httpd policy lacks lnk_read permission
for mysqld_db_t type. While I solved the issue by leaving the socket
file inside the original directory (removing the /var/lib/mysql symlink
and recreating the mysql dir), I was wondering why each symlink type is
specifically allowed
rather than giving any processes a generic access to symlinks.
Is this kind of rule not permitted by selinux? Can it open the door to
other attacks? If so, why? Generally, what is the least invasive
approach to relocate services?
As a side note, consider that the above applies to other common services
as libvirt (fixed via this BZ
https://bugzilla.redhat.com/show_bug.cgi?id=1598593) and mongodb [1].
Thanks.
[1] Another example, from relocating mongodb (this time on a CentOS 7
box):
semanage fcontext -a -e /var/lib/mongo /tank/graylog/var/lib/mongo
mv /var/lib/mongo /tank/graylog/var/lib/mongo
ln -s /tank/graylog/var/lib/mongo /var/lib/mongo
restorecon /var/lib/mongo
systemctl restart mongod
Result:
MongoDB does not start. Issuing "cat /var/log/audit/audit.log |
audit2allow" show the following error: "allow mongod_t
mongod_var_lib_t:lnk_file read;"
Indeed, sesearch can not find any permission to read mongod_var_lib_t
links:
[root@localhost ~]# sesearch -A -s mongod_t | grep lnk_file | grep
mongod_var_lib_t
--
Danti Gionatan
Supporto Tecnico
Assyoma S.r.l. - www.assyoma.it
email: g.danti@xxxxxxxxxx - info@xxxxxxxxxx
GPG public key ID: FF5F32A8
