Relocating mysql

[Gionatan Danti]

Hi all,
I have a question about mysql relocation.

I already created an equivalency rule such as "semanage fcontext --list 
-C" returns the following:
SELinux Local fcontext Equivalence
/mnt/lv_data/var/lib/mysql = /var/lib/mysql

Then I created a symlink in /var/lib:
system_u:object_r:mysqld_db_t:s0    26 May 17 14:39 mysql -> 
/mnt/lv_data/var/lib/mysql

However, httpd/php can not connect to the database. The following 
message is logged in audit.log:
type=AVC msg=audit(1684352064.936:232): avc:  denied  { read } for  
pid=8558 comm="httpd" name="mysql" dev="sda4" ino=147925 
scontext=system_u:system_r:httpd_t:s0 
tcontext=system_u:object_r:mysqld_db_t:s0 tclass=lnk_file permissive=0

My understanding is that httpd can not read the symlink. I expected to 
find a boolean to allow this kind of access, to no avail.

So my question is: can I allow httpd symlink access without manually 
modifying the actual policy (ie: using audit2allow and the likes)?

Thanks.

[Casper]

What is the connection between httpd and mariadb server? Is it Unix
socket file? Or TCP socket?

In the case of TCP socket (port + host), it looks weird for httpd
going to read /var/lib/mysql/

Gionatan Danti a écrit :
> Hi all,
> I have a question about mysql relocation.
>
> I already created an equivalency rule such as "semanage fcontext --list -C"
> returns the following:
> SELinux Local fcontext Equivalence
> /mnt/lv_data/var/lib/mysql = /var/lib/mysql
>
> Then I created a symlink in /var/lib:
> system_u:object_r:mysqld_db_t:s0    26 May 17 14:39 mysql ->
> /mnt/lv_data/var/lib/mysql
>
> However, httpd/php can not connect to the database. The following message is
> logged in audit.log:
> type=AVC msg=audit(1684352064.936:232): avc:  denied  { read } for  pid=8558
> comm="httpd" name="mysql" dev="sda4" ino=147925
> scontext=system_u:system_r:httpd_t:s0
> tcontext=system_u:object_r:mysqld_db_t:s0 tclass=lnk_file permissive=0
>
> My understanding is that httpd can not read the symlink. I expected to find
> a boolean to allow this kind of access, to no avail.
>
> So my question is: can I allow httpd symlink access without manually
> modifying the actual policy (ie: using audit2allow and the likes)?
>
> Thanks.
>
> -- 
> Danti Gionatan
> Supporto Tecnico
> Assyoma S.r.l. - www.assyoma.it
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[Gionatan Danti]

Il 2023-05-18 09:14 Casper ha scritto:
> In the case of TCP socket (port + host), it looks weird for httpd
> going to read /var/lib/mysql/

Hi Casper,
by default php uses unix socket for localhost connection, hence the 
error reported.

Thanks.

[Zdenek Pytela]

Hi Gionatan,

On Wed, May 17, 2023 at 10:10 PM Gionatan Danti  wrote:
> Hi all,
> I have a question about mysql relocation.
>
> I already created an equivalency rule such as "semanage fcontext --list
> -C" returns the following:
> SELinux Local fcontext Equivalence
> /mnt/lv_data/var/lib/mysql = /var/lib/mysql

This is correct.
> Then I created a symlink in /var/lib:
> system_u:object_r:mysqld_db_t:s0    26 May 17 14:39 mysql ->
> /mnt/lv_data/var/lib/mysql
>
> However, httpd/php can not connect to the database. The following
> message is logged in audit.log:
> type=AVC msg=audit(1684352064.936:232): avc:  denied  { read } for
> pid=8558 comm="httpd" name="mysql" dev="sda4" ino=147925
> scontext=system_u:system_r:httpd_t:s0
> tcontext=system_u:object_r:mysqld_db_t:s0 tclass=lnk_file permissive=0
>
> My understanding is that httpd can not read the symlink. I expected to
> find a boolean to allow this kind of access, to no avail.

httpd can only read and write mysql sockets, so far there was no need to
allow other interactions.
> So my question is: can I allow httpd symlink access without manually
> modifying the actual policy (ie: using audit2allow and the likes)?

You can change the value of datadir in mysql configuration.
Otherwise, as in all such changes, you need to create a local policy to
back that change. It can be as easy as

f38# cat local_mysqld_symlink.cil
(allow httpd_t mysqld_db_t (lnk_file (getattr read)))
f38# semodule -i local_mysqld_symlink.cil
> Thanks.
>
> --
> Danti Gionatan
> Supporto Tecnico
> Assyoma S.r.l. - www.assyoma.it
> email: [e-mail] - [e-mail]
> GPG public key ID: FF5F32A8
> _______________________________________________
> selinux mailing list -- [e-mail]
> To unsubscribe send an email to [e-mail]
> Fedora Code of Conduct:
> https://docs.fedoraproject.org/en-US/project/code-of-conduct/
> List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines
> List Archives:
> https://lists.fedoraproject.org/archives/list/[e-mail]...
> Do not reply to spam, report it:
> https://pagure.io/fedora-infrastructure/new_issue

[Gionatan Danti]

Il 2023-05-18 10:39 Zdenek Pytela ha scritto:
> httpd can only read and write mysql sockets, so far there was no need
> to allow other interactions.

Hi Zdenek,
ok, so it is not an error or misconfiguration on my part.
> You can change the value of datadir in mysql configuration.

Yeah, I have taken this approach.
> Otherwise, as in all such changes, you need to create a local policy
> to back that change. It can be as easy as
>
> f38# cat local_mysqld_symlink.cil
> (allow httpd_t mysqld_db_t (lnk_file (getattr read)))
> f38# semodule -i local_mysqld_symlink.cil

When I need to do local policy customizations I generally run 
audit2allow, whose output is (if I am not mistaken) in different format 
than cil. There are any documentations on both format types and their 
differences?

Thanks.