Bug 1146987

Summary:	/bin/su returns segmentation fault for sysadm_r in SELinux policy MLS
Product:	Red Hat Enterprise Linux 7	Reporter:	Matus Marhefka <mmarhefk>
Component:	selinux-policy	Assignee:	Lukas Vrabec <lvrabec>
Status:	CLOSED ERRATA	QA Contact:	Milos Malik <mmalik>
Severity:	high	Docs Contact:
Priority:	high
Version:	7.0	CC:	degts, jjaburek, jreznik, lvrabec, mgrepl, mmalik, mvadkert, plautrba, pvrabec, rhbz, ssekidde, vmojzis
Target Milestone:	beta
Target Release:	---
Hardware:	x86_64
OS:	Linux
Whiteboard:
Fixed In Version:	libselinux-2.5-3.el7	Doc Type:	If docs needed, set a value
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2017-08-01 15:10:10 UTC	Type:	Bug
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:
Bug Blocks:	1218420, 1296594, 1313485, 1377248

Description Matus Marhefka 2014-09-26 13:57:51 UTC

Description of problem:
After changing role to sysadm_r and switching user to root, /bin/su
command returns segmentation fault. This happens only in MLS SELinux
policy in enforcing mode (in permissive mode segmentation fault does
not occure).

# sestatus
SELinux status:                 enabled
SELinuxfs mount:                /sys/fs/selinux
SELinux root directory:         /etc/selinux
Loaded policy name:             mls
Current mode:                   enforcing
Mode from config file:          enforcing
Policy MLS status:              enabled
Policy deny_unknown status:     denied
Max kernel policy version:      28


Version-Release number of selected component (if applicable):
util-linux-2.23.2-16.el7.x86_64
util-linux-2.23.2-17.el7.x86_64


How reproducible:
100%


Steps to Reproduce:
# newrole -r sysadm_r
# /bin/su -
# /bin/su
su: avc.c:74: avc_context_to_sid_raw: Assertion `avc_running' failed.
Segmentation fault
# id -Z
staff_u:sysadm_r:sysadm_t:s0-s15:c0.c1023


Actual results:
Segmentation fault

Expected results:
No segmentation fault

Comment 5 Petr Lautrbach 2016-01-18 09:11:20 UTC

Could you please provide AVCs in permissive mode? libselinux abort's itself as it's not able to create a netlink socket or similar problem with the libselinux initialization.

Comment 6 Miroslav Grepl 2016-01-29 13:46:44 UTC

(In reply to Petr Lautrbach from comment #5)
> Could you please provide AVCs in permissive mode? libselinux abort's itself
> as it's not able to create a netlink socket or similar problem with the
> libselinux initialization.

Yes, it looks like a policy issue.

Comment 7 Petr Lautrbach 2016-01-29 13:51:26 UTC

Probably two issues, one in policy, and the other one in libselinux/su which should abort instead of segfault.

Comment 14 Miroslav Vadkerti 2016-09-27 13:37:34 UTC

I see these events in audit log when doing '/bin/su -':

----
time->Tue Sep 27 15:36:08 2016
type=USER_AVC msg=audit(1474983368.352:2307): pid=10103 uid=0 auid=1000 ses=24 subj=staff_u:sysadm_r:sysadm_su_t:s0-s15:c0.c1023 msg='avc:  can't open netlink socket: 13 (Permission denied)  exe="/usr/bin/su" sauid=0 hostname=? addr=? terminal=?'
----                                                                                                                                                                                                               time->Tue Sep 27 15:36:08 2016
type=SYSCALL msg=audit(1474983368.351:2306): arch=c000003e syscall=41 success=no exit=-13 a0=10 a1=80003 a2=7 a3=1 items=0 ppid=9996 pid=10103 auid=1000 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=pts3 ses=24 comm="su" exe="/usr/bin/su" subj=staff_u:sysadm_r:sysadm_su_t:s0-s15:c0.c1023 key=(null)                                                                                                             type=AVC msg=audit(1474983368.351:2306): avc:  denied  { create } for  pid=10103 comm="su" scontext=staff_u:sysadm_r:sysadm_su_t:s0-s15:c0.c1023 tcontext=staff_u:sysadm_r:sysadm_su_t:s0-s15:c0.c1023 tclass=netlink_selinux_socket
----
time->Tue Sep 27 15:36:08 2016
type=ANOM_ABEND msg=audit(1474983368.352:2308): auid=1000 uid=0 gid=0 ses=24 subj=staff_u:sysadm_r:sysadm_su_t:s0-s15:c0.c1023 pid=10103 comm="su" reason="memory violation" sig=6

Comment 21 Milos Malik 2017-05-02 08:11:55 UTC

Following rule is needed in both targeted and MLS policies:

allow sysadm_su_t self:netlink_selinux_socket { bind create };

If the rule is not present, the scenario fails and triggers following SELinux denials:
----
type=PROCTITLE msg=audit(05/02/2017 03:49:40.696:313) : proctitle=su -c id 
type=SYSCALL msg=audit(05/02/2017 03:49:40.696:313) : arch=x86_64 syscall=socket success=no exit=EACCES(Permission denied) a0=netlink a1=SOCK_RAW a2=cbt a3=0x1 items=0 ppid=1515 pid=1521 auid=unknown(1000) uid=root gid=root euid=root suid=root fsuid=root egid=root sgid=root fsgid=root tty=pts5 ses=4 comm=su exe=/usr/bin/su subj=staff_u:sysadm_r:sysadm_su_t:s0-s0:c0.c1023 key=(null) 
type=AVC msg=audit(05/02/2017 03:49:40.696:313) : avc:  denied  { create } for  pid=1521 comm=su scontext=staff_u:sysadm_r:sysadm_su_t:s0-s0:c0.c1023 tcontext=staff_u:sysadm_r:sysadm_su_t:s0-s0:c0.c1023 tclass=netlink_selinux_socket 
----
type=PROCTITLE msg=audit(05/02/2017 03:55:37.090:374) : proctitle=su -c id 
type=SYSCALL msg=audit(05/02/2017 03:55:37.090:374) : arch=x86_64 syscall=bind success=no exit=EACCES(Permission denied) a0=0x3 a1=0x7ffd8b77ed70 a2=0xc a3=0x1 items=0 ppid=1830 pid=1836 auid=unknown(1000) uid=root gid=root euid=root suid=root fsuid=root egid=root sgid=root fsgid=root tty=pts5 ses=5 comm=su exe=/usr/bin/su subj=staff_u:sysadm_r:sysadm_su_t:s0-s0:c0.c1023 key=(null) 
type=AVC msg=audit(05/02/2017 03:55:37.090:374) : avc:  denied  { bind } for  pid=1836 comm=su scontext=staff_u:sysadm_r:sysadm_su_t:s0-s0:c0.c1023 tcontext=staff_u:sysadm_r:sysadm_su_t:s0-s0:c0.c1023 tclass=netlink_selinux_socket 
----

The automated TC passes after loading of following local policy module:
# cat mypolicy.cil 
( allow sysadm_su_t sysadm_su_t ( netlink_selinux_socket ( create bind )))
#

# rpm -qa selinux-policy\*
selinux-policy-3.13.1-144.el7.noarch
selinux-policy-targeted-3.13.1-144.el7.noarch
selinux-policy-mls-3.13.1-144.el7.noarch
#

Comment 24 errata-xmlrpc 2017-08-01 15:10:10 UTC

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2017:1861