On Sun, 11 Jul 2010 14:01:08 +0200, Dominick Grift wrote:
> On Sat, Jul 10, 2010 at 09:36:30PM +0100, Ted Rule wrote:
>
>> In the course of trying to get a syslog-ng daemon running on a
>> non-standard TCP port on CentOS5, I came across an AVC for the port
>> which appeared
>> to already have a permission in the SELinux Policy.
>>
>>
>> We tried to make syslog-ng listen on TCP Port 5514, and as a result we
>> got the following set of audit messages:
>>
>>
>> $ sudo ausearch -ts yesterday -c syslog-ng
>> ----
>> time->Fri Jul 9 23:04:26 2010
>> type=SYSCALL msg=audit(1278713066.242:269066): arch=40000003 syscall=102
>> success=no exit=-13 a0=2 a1=bfb34210 a2=95b51e8 a3=6 items=0 ppid=1
>> pid=1713 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0
>> fsgid=0 tty=(none) ses=4294967295 comm="syslog-ng" exe="/sbin/syslog-ng"
>> subj=system_u:system_r:syslogd_t:s0 key=(null)
>> type=AVC msg=audit(1278713066.242:269066): avc: denied { name_bind }
>> for pid=1713 comm="syslog-ng" src=5514
>> scontext=system_u:system_r:syslogd_t:s0
>> tcontext=system_u:object_r:port_t:s0 tclass=tcp_socket
>> ----
>> time->Fri Jul 9 23:04:26 2010
>> type=ANOM_ABEND msg=audit(1278713066.291:269067): auid=4294967295 uid=0
>> gid=0 ses=4294967295 subj=system_u:system_r:syslogd_t:s0 pid=1713
>> comm="syslog-ng" sig=11
>> ----
>> time->Fri Jul 9 23:27:59 2010
>> type=SYSCALL msg=audit(1278714479.797:269169): arch=40000003 syscall=102
>> success=no exit=-13 a0=2 a1=bffe96d0 a2=97a6928 a3=6 items=0 ppid=1
>> pid=15354 auid=500 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0
>> fsgid=0 tty=(none) ses=44818 comm="syslog-ng" exe="/sbin/syslog-ng"
>> subj=user_u:system_r:syslogd_t:s0 key=(null)
>> type=AVC msg=audit(1278714479.797:269169): avc: denied { name_bind }
>> for pid=15354 comm="syslog-ng" src=5514
>> scontext=user_u:system_r:syslogd_t:s0
>> tcontext=system_u:object_r:port_t:s0 tclass=tcp_socket
>> ----
>> time->Fri Jul 9 23:27:59 2010
>> type=ANOM_ABEND msg=audit(1278714479.833:269170): auid=500 uid=0 gid=0
>> ses=44818 subj=user_u:system_r:syslogd_t:s0 pid=15354 comm="syslog-ng"
>> sig=11
>> $
>>
>> However, despite the fact that the AVC suggested that we needed to add
>> the permission:
>>
>> allow syslogd_t port_t : tcp_socket { name_bind name_connect };
>>
>>
>>
>> an sesearch suggests that the permission already exists:
>>
>> $ sudo sesearch --allow -s syslogd_t | grep tcp |grep name.bind
>> allow syslogd_t rsh_port_t : tcp_socket { name_bind name_connect };
>> allow syslogd_t syslogd_port_t : tcp_socket { name_bind name_connect };
>> allow syslogd_t port_t : tcp_socket { name_bind name_connect };
>> allow syslogd_t reserved_port_t : tcp_socket { name_bind name_connect };
>> $
>>
>
>
> sesearch -SC --allow -s syslogd_t -t port_t
> Found 8 semantic av rules:
> allow syslogd_t port_type : tcp_socket { recv_msg send_msg } ;
> allow syslogd_t port_type : udp_socket { recv_msg send_msg } ;
> DT allow syslogd_t port_type : tcp_socket { recv_msg send_msg } ; [ allow_kerberos ]
> DT allow syslogd_t port_type : tcp_socket { recv_msg send_msg } ; [ allow_ypbind ]
> DT allow syslogd_t port_type : udp_socket { recv_msg send_msg } ; [ allow_kerberos ]
> DT allow syslogd_t port_type : udp_socket { recv_msg send_msg } ; [ allow_ypbind ]
> DT allow syslogd_t port_t : tcp_socket { name_bind name_connect } ; [ allow_ypbind ]
> DT allow syslogd_t port_t : udp_socket name_bind ; [ allow_ypbind ]
>
> ... This means that syslogd_t is only allowed to bind udp/tc sockets to ports with type port_t is booolean allow_ypbind is set to true.
>
>
>> Eventually, we repaired the situation by adding TCP/5514 as a
>> syslogd_port_t, as in:
>>
>> $ sudo semanage port -l |grep 514
>> cluster_port_t tcp 5149, 40040, 50006, 50007, 50008
>> cluster_port_t udp 5149, 50006, 50007, 50008
>> rsh_port_t tcp 514
>> syslogd_port_t tcp 5514
>> syslogd_port_t udp 514
>> virt_port_t tcp 16509, 16514
>> virt_port_t udp 16509, 16514
>> $
>>
>>
>
> Good decision
>
>
>> But my curiousity is piqued. Why did the policy deny the binding to a
>> type port_t, when the policy appeared to already allow this?
>>
>>
>> FWIW, the policy at the moment is a somewhat aged:
>>
>> selinux-policy-targeted-2.4.6-203.el5
>>
>>
>
> Because it a tunable policy rules that obviously currently is toggled to false. Piping the avc denial into audit2why should suggest that
>
> # echo "type=AVC msg=audit(1278714479.797:269169): avc: denied { name_bind } for pid=15354 comm="syslog-ng" src=5514 scontext=system_u:system_r:syslogd_t:s0 tcontext=system_u:object_r:port_t:s0 tclass=tcp_socket" | audit2why
> type=AVC msg=audit(1278714479.797:269169): avc: denied { name_bind } for pid=15354 comm=syslog-ng src=5514 scontext=system_u:system_r:syslogd_t:s0 tcontext=system_u:object_r:port_t:s0 tclass=tcp_socket
>
> Was caused by:
> The boolean allow_ypbind was set incorrectly.
> Description:
> Allow system to run with NIS
>
> Allow access by executing:
> # setsebool -P allow_ypbind 1
>
>
>
Thanks for the explanation, but I must say that sesearch's -C provision
breaks the golden Principle of Least Surprise for me. Surely sesearch
run without -C,
and even more so when run without an explicit policy filename, should
only print out currently active policy rules. i.e. it should only list
those tunable policy rules which are active by reason of the state of
the corresponding boolean?
As it stands, all tunable policy rules - enabled or disabled - are
listed in sesearch's output. Hence my original confusion.
I think my vote would be for a complete deprecation of the -C option, so
that sesearch always runs as if it had been included on the command line.
Example listing for this problem:
$ sudo sesearch --allow -s syslogd_t -t port_t
Found 6 semantic av rules:
allow syslogd_t port_type : tcp_socket { recv_msg send_msg } ;
allow syslogd_t port_type : udp_socket { recv_msg send_msg } ;
allow syslogd_t port_type : tcp_socket { recv_msg send_msg } ;
allow syslogd_t port_type : udp_socket { recv_msg send_msg } ;
allow syslogd_t port_t : tcp_socket { name_bind name_connect } ;
allow syslogd_t port_t : udp_socket name_bind ;
$ sudo sesearch -C --allow -s syslogd_t -t port_t
Found 6 semantic av rules:
allow syslogd_t port_type : tcp_socket { recv_msg send_msg } ;
allow syslogd_t port_type : udp_socket { recv_msg send_msg } ;
DT allow syslogd_t port_type : tcp_socket { recv_msg send_msg } ; [
allow_ypbind ]
DT allow syslogd_t port_type : udp_socket { recv_msg send_msg } ; [
allow_ypbind ]
DT allow syslogd_t port_t : tcp_socket { name_bind name_connect } ; [
allow_ypbind ]
DT allow syslogd_t port_t : udp_socket name_bind ; [ allow_ypbind ]
$
--
Ted Rule
Director, Layer3 Systems Ltd
http://www.layer3.co.uk/
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