oddity with postfix delivering to homedir
Manuel Wolfshant
wolfy at nobugconsulting.ro
Tue Feb 17 22:48:43 UTC 2009
On 02/17/2009 07:59 PM, Daniel J Walsh wrote:
> Manuel Wolfshant wrote:
>
>> Daniel J Walsh wrote:
>>
>>> Manuel Wolfshant wrote:
>>>
>>>
>>>> Daniel J Walsh wrote:
>>>>
>>>>
>>>>> Manuel Wolfshant wrote:
>>>>>
>>>>>
>>>>>
>>>>>> hello
>>>>>>
>>>>>> I have migrated a working mailserver from Centos 4.7 to Centos 5.2.
>>>>>> The system uses postfix to receive messages from a mail relay and is
>>>>>> supposed to deliver them to folders named after the users, following
>>>>>> the /home/firstname.lastname at domain template. Authentication is
>>>>>> done via
>>>>>> mysql against a db running on another system.
>>>>>> New accounts are created automatically when a mail has to be
>>>>>> delivered to an user which has never been seen before.
>>>>>> For the users which existed before migration, everything is fine.
>>>>>> However, for non-existing (i.e. to be created) users the homedir is
>>>>>> created with wrong contexts, which prohibit postfix to finalize the
>>>>>> delivery. Once a message is received for a new user, the following is
>>>>>> created:
>>>>>>
>>>>>> [root at imap2 ~]# ll -Zl /home/gigi.test\@nobugconsulting.ro/ -R
>>>>>> /home/gigi.test at nobugconsulting.ro/: total
>>>>>> 8 drwx------ 2
>>>>>> root:object_r:home_root_t postfix postfix 4096 Feb 17 01:05 tmp
>>>>>>
>>>>>> /home/gigi.test at nobugconsulting.ro/tmp:
>>>>>> total 4 -rw------- 1
>>>>>> root:object_r:home_root_t postfix postfix 0 Feb 17 01:05
>>>>>> 1234825528.P26797.imap2
>>>>>>
>>>>>> After that postfix tries to do stuff on the newly created file and
>>>>>> selinux kicks in and denies access.
>>>>>> Running restorecon at this point fixes things:
>>>>>>
>>>>>> [root at imap2 ~]# restorecon -v -R
>>>>>> /home/gigi.test at nobugconsulting.ro
>>>>>> restorecon reset /home/gigi.test at nobugconsulting.ro context
>>>>>> root:object_r:home_root_t:s0->user_u:object_r:user_home_dir_t:s0
>>>>>> restorecon reset /home/gigi.test at nobugconsulting.ro/tmp context
>>>>>> root:object_r:home_root_t:s0->user_u:object_r:user_home_t:s0
>>>>>> restorecon reset
>>>>>> /home/gigi.test at nobugconsulting.ro/tmp/1234825528.P26797.imap2 context
>>>>>> root:object_r:home_root_t:s0->user_u:object_r:user_home_t:s0
>>>>>>
>>>>>>
>>>>>>
>>>>>> I am running the following versions of packages:
>>>>>>
>>>>>> [root at imap2 ~]# rpm -qa kernel\* \*selinux\* postfix\*
>>>>>> kernel-xen-2.6.18-92.1.22.el5
>>>>>> libselinux-utils-1.33.4-5.1.el5
>>>>>> selinux-policy-targeted-2.4.6-203.el5
>>>>>> libselinux-1.33.4-5.1.el5
>>>>>> libselinux-python-1.33.4-5.1.el5
>>>>>> selinux-policy-2.4.6-203.el5
>>>>>> postfix-2.3.3-2.1.centos.mysql_pgsql
>>>>>>
>>>>>> Selinux related packages have been upgraded last night in the
>>>>>> hope to
>>>>>> fix the problem, postfix is almost stock centosplus 5.2, recompiled
>>>>>> with
>>>>>> support for mysql but without postgresql- support.
>>>>>>
>>>>>> Obviously I no not want to follow the result of audit2allow,
>>>>>> home_root_t:dir should not be there in the first place:
>>>>>> [root at imap2 ~]# grep avc /var/log/audit/audit.log|audit2allow
>>>>>>
>>>>>> #============= postfix_virtual_t ==============
>>>>>> allow postfix_virtual_t home_root_t:dir { write remove_name create
>>>>>> add_name };
>>>>>> allow postfix_virtual_t home_root_t:file { write create unlink link
>>>>>> getattr };
>>>>>> allow postfix_virtual_t postfix_private_t:dir search;
>>>>>> allow postfix_virtual_t postfix_private_t:sock_file write;
>>>>>> allow postfix_virtual_t usr_t:file { read getattr };
>>>>>>
>>>>>> Correct access rights and contexts seem to be:
>>>>>> [root at imap2 ~]# ls -l /home/ -dZ
>>>>>> drwxr-xr-x+ postfix postfix system_u:object_r:home_root_t /home/
>>>>>> [root at imap2 ~]# ls -l /home/gigi.test\@nobugconsulting.ro/ -dZ
>>>>>> drwx------ postfix postfix user_u:object_r:user_home_dir_t
>>>>>> /home/gigi.test at nobugconsulting.ro/
>>>>>>
>>>>>> The only user on the system (beside root) is postfix:
>>>>>> [root at imap2 ~]# getent passwd postfix
>>>>>> postfix:x:89:89::/var/spool/postfix:/sbin/nologin
>>>>>>
>>>>>> [...]
>>>>>>
>>>>>> My questions are
>>>>>> a) why does postfix create the initial home directories with a wrong
>>>>>> context ? Note this only happens for NEW users, messages for the users
>>>>>> which already existed [and have correct context] on the old system are
>>>>>> perfectly fine.
>>>>>>
>>>>>>
>>>>> Does postfix actually create the homedir or was the homedir created by
>>>>> an init script? postfix does not know anything about SELinux but there
>>>>> are rules about processes running as postfix_t creating files in
>>>>> user_home_dir_t directories. In your case it seems that the directory
>>>>> was labeled home_root_t, which is where the problem is.
>>>>>
>>>>>
>>>>>
>>>> /home exists; everything below it is created (and should be created
>>>> with correct contexts) by postfix in real time
>>>>
>>>>
>>>>
>>> Why is postfix creating a homedir?
>>>
>> Because that's where all the virtual users have their mails.
>>
>>
>>
>>> I have never seen this before.
>>> That is where the problem is, selinux policy does not allow postfix to
>>> create directories under /home (home_root_t), so it is being blocked.
>>>
>>>
>>>
>> I am sorry, I do not remember from which site was the setup taken. 4
>> years or so since I installed it the first time in Centos 4.2, but if I
>> am not mistaken it's an almost exact replica of the setup suggested by
>> postfixadmin
>>
>>
>
> So postfix_virtual creates the homedir just to put a file in it and then
> send it somewhere else?
>
> If this is standard I can allow it, although it seems pretty strange.
>
To be honest, I am not 100% sure how standard that is, although I am
pretty sure that delivering to home dirs is not uncommon. Fact is that
(in my case) postfix is the only user on the box and owns all the
directories created below /home. Technically I presume that the whole
structure could be moved anywhere else, but 4 years ago /home seemed a
logical place, even if all users are virtual and defined in mysql.
Basically when doing a deliver, postfix uses maildirmake to create the
top-level directory assigned to any specific user, leading to a tree
like this:
/home
/home/specific.user
/home/specific.user/cur (cur stands for current)
/home/specific.user/tmp
/home/specific.user/new
The structure gets created when the very first message for a user is
received.
As far as I have understood (it always "just worked" so I never did
in-depth digging), messages are first created in /home/specific.user/tmp
and after that copied to the final delivery place i.e.
/home/specific.user/new. Once the user reads the message (via an imap /
pop daemon), the message is transferred to /home/specific.user/cur (or
to other folders, created via the IMAP daemon, but all of them placed
below /home/specific.user)
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