On 04/07/2009 08:30 AM, Stephen Smalley wrote:
On Sun, 2009-04-05 at 20:34 +0200, Sebastian Pfaff wrote:
hello,
i'm not sure about this: but afaik to bind a socket to a port the
name_bind is neccessary (please correct me, if this wrong).
now try this:
==========
policy_module(NETCAT, 0.0.1)
require { type unconfined_t; }
role unconfined_r types nc_t ;
type nc_t;
type nc_exec_t;
application_domain(nc_t, nc_exec_t)
domain_auto_transition_pattern(unconfined_t, nc_exec_t, nc_t)
#EOF
build load NETCAT.te:
==================
make -f /usr/share/selinux/devel/Makefile
sudo semodule -i NETCAT.pp
then set domain nc_t permissive:
==========================
sudo semanage permissive -a nc_t
(temporarily) change type of nc:
=========================
sudo chcon -v -t nc_exec_t /usr/bin/nc
and then start a netcat "server" :
=========================
nc -l 44444
here the verification that nc listens on 44444 for incoming connections:
=======================================================
[root@SecLab ~]# netstat -plntZ | grep 44444
tcp 0 0 127.0.0.1:44444
0.0.0.0:* LISTEN 10279/nc
unconfined_u:unconfined_r:nc_t:s0
now we check audit.log:
===================
[root@SecLab ~]# grep '^type=AVC' /var/log/audit/audit.log
type=AVC msg=audit(1238954202.516:257): avc: denied { read write }
for pid=10279 comm="nc" name="1" dev=devpts ino=3
scontext=unconfined_u:unconfined_r:nc_t:s0
tcontext=unconfined_u:object_r:unconfined_devpts_t:s0 tclass=chr_file
type=AVC msg=audit(1238954202.518:258): avc: denied { read } for
pid=10279 comm="nc" name="ld.so.cache" dev=sda1 ino=34611
scontext=unconfined_u:unconfined_r:nc_t:s0
tcontext=system_u:object_r:ld_so_cache_t:s0 tclass=file
type=AVC msg=audit(1238954202.518:259): avc: denied { getattr } for
pid=10279 comm="nc" path="/etc/ld.so.cache" dev=sda1 ino=34611
scontext=unconfined_u:unconfined_r:nc_t:s0
tcontext=system_u:object_r:ld_so_cache_t:s0 tclass=file
type=AVC msg=audit(1238954202.518:260): avc: denied { read } for
pid=10279 comm="nc" name="libglib-2.0.so.0" dev=sda1 ino=229602
scontext=unconfined_u:unconfined_r:nc_t:s0
tcontext=system_u:object_r:lib_t:s0 tclass=lnk_file
type=AVC msg=audit(1238954202.518:260): avc: denied { read } for
pid=10279 comm="nc" name="libglib-2.0.so.0.1800.4" dev=sda1 ino=229574
scontext=unconfined_u:unconfined_r:nc_t:s0
tcontext=system_u:object_r:lib_t:s0 tclass=file
type=AVC msg=audit(1238954202.519:261): avc: denied { getattr } for
pid=10279 comm="nc" path="/lib/libglib-2.0.so.0.1800.4" dev=sda1
ino=229574 scontext=unconfined_u:unconfined_r:nc_t:s0
tcontext=system_u:object_r:lib_t:s0 tclass=file
type=AVC msg=audit(1238954202.519:262): avc: denied { execute } for
pid=10279 comm="nc" path="/lib/libglib-2.0.so.0.1800.4" dev=sda1
ino=229574 scontext=unconfined_u:unconfined_r:nc_t:s0
tcontext=system_u:object_r:lib_t:s0 tclass=file
type=AVC msg=audit(1238954202.519:263): avc: denied { read } for
pid=10279 comm="nc" path="/lib/ld-2.9.so" dev=sda1 ino=229558
scontext=unconfined_u:unconfined_r:nc_t:s0
tcontext=system_u:object_r:ld_so_t:s0 tclass=file
type=AVC msg=audit(1238954202.520:264): avc: denied { create } for
pid=10279 comm="nc" scontext=unconfined_u:unconfined_r:nc_t:s0
tcontext=unconfined_u:unconfined_r:nc_t:s0 tclass=netlink_route_socket
type=AVC msg=audit(1238954202.520:265): avc: denied { bind } for
pid=10279 comm="nc" scontext=unconfined_u:unconfined_r:nc_t:s0
tcontext=unconfined_u:unconfined_r:nc_t:s0 tclass=netlink_route_socket
type=AVC msg=audit(1238954202.520:266): avc: denied { getattr } for
pid=10279 comm="nc" scontext=unconfined_u:unconfined_r:nc_t:s0
tcontext=unconfined_u:unconfined_r:nc_t:s0 tclass=netlink_route_socket
type=AVC msg=audit(1238954202.520:267): avc: denied { write } for
pid=10279 comm="nc" scontext=unconfined_u:unconfined_r:nc_t:s0
tcontext=unconfined_u:unconfined_r:nc_t:s0 tclass=netlink_route_socket
type=AVC msg=audit(1238954202.520:267): avc: denied { nlmsg_read }
for pid=10279 comm="nc" scontext=unconfined_u:unconfined_r:nc_t:s0
tcontext=unconfined_u:unconfined_r:nc_t:s0 tclass=netlink_route_socket
type=AVC msg=audit(1238954202.520:268): avc: denied { read } for
pid=10279 comm="nc" scontext=unconfined_u:unconfined_r:nc_t:s0
tcontext=unconfined_u:unconfined_r:nc_t:s0 tclass=netlink_route_socket
type=AVC msg=audit(1238954202.533:269): avc: denied { read } for
pid=10279 comm="nc" name="nsswitch.conf" dev=sda1 ino=32805
scontext=unconfined_u:unconfined_r:nc_t:s0
tcontext=system_u:object_r:etc_t:s0 tclass=file
type=AVC msg=audit(1238954202.533:270): avc: denied { getattr } for
pid=10279 comm="nc" path="/etc/nsswitch.conf" dev=sda1 ino=32805
scontext=unconfined_u:unconfined_r:nc_t:s0
tcontext=system_u:object_r:etc_t:s0 tclass=file
type=AVC msg=audit(1238954202.534:271): avc: denied { read } for
pid=10279 comm="nc" name="resolv.conf" dev=sda1 ino=34021
scontext=unconfined_u:unconfined_r:nc_t:s0
tcontext=system_u:object_r:net_conf_t:s0 tclass=file
type=AVC msg=audit(1238954202.534:272): avc: denied { getattr } for
pid=10279 comm="nc" path="/etc/resolv.conf" dev=sda1 ino=34021
scontext=unconfined_u:unconfined_r:nc_t:s0
tcontext=system_u:object_r:net_conf_t:s0 tclass=file
type=AVC msg=audit(1238954202.535:273): avc: denied { create } for
pid=10279 comm="nc" scontext=unconfined_u:unconfined_r:nc_t:s0
tcontext=unconfined_u:unconfined_r:nc_t:s0 tclass=tcp_socket
type=AVC msg=audit(1238954202.535:274): avc: denied { setopt } for
pid=10279 comm="nc" scontext=unconfined_u:unconfined_r:nc_t:s0
tcontext=unconfined_u:unconfined_r:nc_t:s0 tclass=tcp_socket
type=AVC msg=audit(1238954202.535:275): avc: denied { bind } for
pid=10279 comm="nc" scontext=unconfined_u:unconfined_r:nc_t:s0
tcontext=unconfined_u:unconfined_r:nc_t:s0 tclass=tcp_socket
type=AVC msg=audit(1238954202.535:275): avc: denied { node_bind }
for pid=10279 comm="nc" saddr=127.0.0.1 src=44444
scontext=unconfined_u:unconfined_r:nc_t:s0
tcontext=system_u:object_r:lo_node_t:s0 tclass=tcp_socket
type=AVC msg=audit(1238954202.535:276): avc: denied { listen } for
pid=10279 comm="nc" laddr=127.0.0.1 lport=44444
scontext=unconfined_u:unconfined_r:nc_t:s0
tcontext=unconfined_u:unconfined_r:nc_t:s0 tclass=tcp_socket
type=AVC msg=audit(1238954202.535:277): avc: denied { accept } for
pid=10279 comm="nc" laddr=127.0.0.1 lport=44444
scontext=unconfined_u:unconfined_r:nc_t:s0
tcontext=unconfined_u:unconfined_r:nc_t:s0 tclass=tcp_socket
As everybody can see, there is no name_bind permission. why is this
so? I always thought, that name_bind is necessary to bind a port. An
entry from dan's blog teached me, that name_bind is always(?) needed.
I'm relatively new to selinux, so i'm not sure about this. Hope
someone can help me.
I'm using fedora 10. Btw: sesearch --allow -s nc_t | grep name_bind
finds nothing. if you need additional info, please let me know.
name_bind is not checked when the port falls within the local port range
(cat /proc/sys/net/ipv4/ip_local_port_range), since ports in that range
are used for auto-binding of unbound sockets and thus aren't truly
controllable (unless we were to further modify the kernel to apply a
check when scanning that port range for auto-binding and to skip port
numbers in that range on a denial). name_bind was primarily intended to
control the ability to bind to well known ports to prevent spoofing of a
given service by another process.
I think this is a mistake. I think we should prevent name_bind of any
service, to ensure a user is not running malicious software in his
homedirectory that is listening on a port. Obviously we are blocking
via firewall high level ports but we block the first 32000 ports now and
it makes no logical sense to not block all.
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