oddity with postfix delivering to homedir
Manuel Wolfshant
wolfy at nobugconsulting.ro
Tue Feb 17 13:44:16 UTC 2009
Daniel J Walsh wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> 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
>>
>> raw content of audit log after a failed delivery for a never-seen
>> before user:
>> type=AVC msg=audit(1234873447.682:45616): avc: denied { write } for
>> pid=2958 comm="virtual"
>> path="/home/gigi.test at nobugconsulting.ro/tmp/1234873447.P2958.imap2"
>> dev=hda1 ino=2736137 scontext=root:system_r:postfix_virtual_t:s0
>> tcontext=root:object_r:home_root_t:s0 tclass=file
>> type=SYSCALL msg=audit(1234873447.682:45616): arch=c000003e syscall=1
>> success=no exit=-13 a0=c a1=2b96176fe510 a2=1b5 a3=7228206f722e676e
>> items=0 ppid=26787 pid=2958 auid=0 uid=0 gid=0 euid=89 suid=0 fsuid=89
>> egid=89 sgid=0 fsgid=89 tty=(none) ses=7290 comm="virtual"
>> exe="/usr/libexec/postfix/virtual"
>> subj=root:system_r:postfix_virtual_t:s0 key=(null)
>> type=AVC msg=audit(1234873447.710:45617): avc: denied { write } for
>> pid=2958 comm="virtual" name="1234873447.P2958.imap2" dev=hda1
>> ino=2736137 scontext=root:system_r:postfix_virtual_t:s0
>> tcontext=root:object_r:home_root_t:s0 tclass=file
>> type=SYSCALL msg=audit(1234873447.710:45617): arch=c000003e syscall=77
>> success=no exit=-13 a0=c a1=0 a2=2 a3=0 items=0 ppid=26787 pid=2958
>> auid=0 uid=0 gid=0 euid=89 suid=0 fsuid=89 egid=89 sgid=0 fsgid=89
>> tty=(none) ses=7290 comm="virtual" exe="/usr/libexec/postfix/virtual"
>> subj=root:system_r:postfix_virtual_t:s0 key=(null)
>> type=AVC msg=audit(1234873447.710:45618): avc: denied { remove_name }
>> for pid=2958 comm="virtual" name="1234873447.P2958.imap2"
>> dev=hda1ino=2736137 scontext=root:system_r:postfix_virtual_t:s0
>> tcontext=root:object_r:home_root_t:s0 tclass=dir
>> type=SYSCALL msg=audit(1234873447.710:45618): arch=c000003e syscall=87
>> success=no exit=-13 a0=2b96176fdb80 a1=64 a2=4 a3=2b95fb0340ec items=0
>> ppid=26787 pid=2958 auid=0 uid=0 gid=0 euid=89 suid=0 fsuid=89 egid=89
>> sgid=0 fsgid=89 tty=(none) ses=7290 comm="virtual"
>> exe="/usr/libexec/postfix/virtual"
>> subj=root:system_r:postfix_virtual_t:s0 key=(null)
>>
>>
>>
>>
>>
>>
>> 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
>> b) what can I do to fix ?
>>
>>
> The restorecon should have fixed the homedir problem,
I asssume you mean restorecond ? It's running ...
> the other policy I will add to the 5.4 update.
>
> selinux-policy-2.4.6-213.el5 Should be up on
> http://people.redhat.com/dwalsh/RHEL5/
>
> Soon
>
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