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Bug 1719754 - SELinux prevents cups-browsed from creating a symlink in /tmp
Summary: SELinux prevents cups-browsed from creating a symlink in /tmp
Keywords:
Status: CLOSED ERRATA
Alias: None
Product: Red Hat Enterprise Linux 7
Classification: Red Hat
Component: selinux-policy
Version: 7.7
Hardware: All
OS: Linux
medium
medium
Target Milestone: rc
: 7.8
Assignee: Lukas Vrabec
QA Contact: Milos Malik
URL:
Whiteboard:
: 1756489 (view as bug list)
Depends On:
Blocks:
TreeView+ depends on / blocked
 
Reported: 2019-06-12 13:19 UTC by Petr Sklenar
Modified: 2020-03-31 19:11 UTC (History)
11 users (show)

Fixed In Version:
Doc Type: If docs needed, set a value
Doc Text:
Clone Of:
Environment:
Last Closed: 2020-03-31 19:10:50 UTC
Target Upstream Version:
Embargoed:

Attachments (Terms of Use)


Links
System ID Private Priority Status Summary Last Updated
Red Hat Product Errata RHBA-2020:1007 0 None None None 2020-03-31 19:11:18 UTC

Description Petr Sklenar 2019-06-12 13:19:50 UTC 
Description of problem:
there are plenty of avc denial when running cups-browsed

Version-Release number of selected component (if applicable):
cups-1.6.3-40.el7.x86_64
selinux-policy-3.13.1-250.el7.noarch

RHEL-7.7-20190606.1

How reproducible:
always

Steps to Reproduce:
 
        echo 'BrowseRemoteProtocols dnssd cups' >> /etc/cups/cups-browsed.conf
        echo 'BrowsePoll cups<server>:631' >> /etc/cups/cups-browsed.conf
        service cups restart
        service cups-browsed restart

Actual results:
type=PROCTITLE msg=audit(06/12/2019 09:13:20.250:206316) : proctitle=/usr/sbin/cups-browsed 
type=SYSCALL msg=audit(06/12/2019 09:13:20.250:206316) : arch=x86_64 syscall=symlink success=no exit=EACCES(Permission denied) a0=0x7ffce9dd8ed0 a1=0x5557da53e718 a2=0x5557da53e72a a3=0x5d00fa70 items=0 ppid=1 pid=10999 auid=unset uid=root gid=root euid=root suid=root fsuid=root egid=root sgid=root fsgid=root tty=(none) ses=unset comm=cups-browsed exe=/usr/sbin/cups-browsed subj=system_u:system_r:cupsd_t:s0-s0:c0.c1023 key=(null) 
type=AVC msg=audit(06/12/2019 09:13:20.250:206316) : avc:  denied  { create } for  pid=10999 comm=cups-browsed name=5d00fa703d7d4 scontext=system_u:system_r:cupsd_t:s0-s0:c0.c1023 tcontext=system_u:object_r:tmp_t:s0 tclass=lnk_file permissive=0 
----
type=PROCTITLE msg=audit(06/12/2019 09:13:20.250:206317) : proctitle=/usr/sbin/cups-browsed 
type=SYSCALL msg=audit(06/12/2019 09:13:20.250:206317) : arch=x86_64 syscall=symlink success=no exit=EACCES(Permission denied) a0=0x7ffce9dd8ed0 a1=0x5557da53e718 a2=0x5557da53e72a a3=0x5d00fa70 items=0 ppid=1 pid=10999 auid=unset uid=root gid=root euid=root suid=root fsuid=root egid=root sgid=root fsgid=root tty=(none) ses=unset comm=cups-browsed exe=/usr/sbin/cups-browsed subj=system_u:system_r:cupsd_t:s0-s0:c0.c1023 key=(null) 
type=AVC msg=audit(06/12/2019 09:13:20.250:206317) : avc:  denied  { create } for  pid=10999 comm=cups-browsed name=5d00fa703d81a scontext=system_u:system_r:cupsd_t:s0-s0:c0.c1023 tcontext=system_u:object_r:tmp_t:s0 tclass=lnk_file permissive=0 

Expected results:


Additional info:
Comment 5 Milos Malik 2019-06-12 13:37:35 UTC 
Following SELinux denials appear in permissive mode:
----
type=PROCTITLE msg=audit(06/12/2019 09:35:19.758:2613) : proctitle=/usr/sbin/cups-browsed 
type=PATH msg=audit(06/12/2019 09:35:19.758:2613) : item=2 name=/tmp/5d00ff97b9623 inode=389400 dev=fd:01 mode=link,777 ouid=root ogid=root rdev=00:00 obj=system_u:object_r:tmp_t:s0 objtype=CREATE cap_fp=none cap_fi=none cap_fe=0 cap_fver=0 
type=PATH msg=audit(06/12/2019 09:35:19.758:2613) : item=1 name=/tmp/ inode=74 dev=fd:01 mode=dir,sticky,777 ouid=root ogid=root rdev=00:00 obj=system_u:object_r:tmp_t:s0 objtype=PARENT cap_fp=none cap_fi=none cap_fe=0 cap_fver=0 
type=PATH msg=audit(06/12/2019 09:35:19.758:2613) : item=0 name=/etc/cups/ppd/brno1-0th-cafe.ppd objtype=UNKNOWN cap_fp=none cap_fi=none cap_fe=0 cap_fver=0 
type=CWD msg=audit(06/12/2019 09:35:19.758:2613) :  cwd=/ 
type=SYSCALL msg=audit(06/12/2019 09:35:19.758:2613) : arch=x86_64 syscall=symlink success=yes exit=0 a0=0x7ffc8a5289e0 a1=0x55a60d83f718 a2=0x55a60d83f72a a3=0x7ffc8a527020 items=3 ppid=1 pid=22375 auid=unset uid=root gid=root euid=root suid=root fsuid=root egid=root sgid=root fsgid=root tty=(none) ses=unset comm=cups-browsed exe=/usr/sbin/cups-browsed subj=system_u:system_r:cupsd_t:s0-s0:c0.c1023 key=(null) 
type=AVC msg=audit(06/12/2019 09:35:19.758:2613) : avc:  denied  { create } for  pid=22375 comm=cups-browsed name=5d00ff97b9623 scontext=system_u:system_r:cupsd_t:s0-s0:c0.c1023 tcontext=system_u:object_r:tmp_t:s0 tclass=lnk_file permissive=1 
----
type=PROCTITLE msg=audit(06/12/2019 09:35:19.761:2614) : proctitle=/usr/sbin/cups-browsed 
type=PATH msg=audit(06/12/2019 09:35:19.761:2614) : item=1 name=/tmp/5d00ff97b9623 inode=389400 dev=fd:01 mode=link,777 ouid=root ogid=root rdev=00:00 obj=system_u:object_r:tmp_t:s0 objtype=DELETE cap_fp=none cap_fi=none cap_fe=0 cap_fver=0 
type=PATH msg=audit(06/12/2019 09:35:19.761:2614) : item=0 name=/tmp/ inode=74 dev=fd:01 mode=dir,sticky,777 ouid=root ogid=root rdev=00:00 obj=system_u:object_r:tmp_t:s0 objtype=PARENT cap_fp=none cap_fi=none cap_fe=0 cap_fver=0 
type=CWD msg=audit(06/12/2019 09:35:19.761:2614) :  cwd=/ 
type=SYSCALL msg=audit(06/12/2019 09:35:19.761:2614) : arch=x86_64 syscall=unlink success=yes exit=0 a0=0x55a60d83f718 a1=0x0 a2=0x7ff9681ea7b8 a3=0x7ff9681ea7b8 items=2 ppid=1 pid=22375 auid=unset uid=root gid=root euid=root suid=root fsuid=root egid=root sgid=root fsgid=root tty=(none) ses=unset comm=cups-browsed exe=/usr/sbin/cups-browsed subj=system_u:system_r:cupsd_t:s0-s0:c0.c1023 key=(null) 
type=AVC msg=audit(06/12/2019 09:35:19.761:2614) : avc:  denied  { unlink } for  pid=22375 comm=cups-browsed name=5d00ff97b9623 dev="vda1" ino=389400 scontext=system_u:system_r:cupsd_t:s0-s0:c0.c1023 tcontext=system_u:object_r:tmp_t:s0 tclass=lnk_file permissive=1 
----

The amount of SELinux denials triggered by the reproducer in enforcing mode is huge (thousands).
Comment 6 Milos Malik 2019-06-12 13:41:52 UTC 
# rpm -qa selinux\*
selinux-policy-devel-3.13.1-251.el7.noarch
selinux-policy-targeted-3.13.1-251.el7.noarch
selinux-policy-mls-3.13.1-251.el7.noarch
selinux-policy-3.13.1-251.el7.noarch
# sesearch -s cupsd_t -t tmp_t -T
Found 3 semantic te rules:
   type_transition cupsd_t tmp_t : dir cupsd_tmp_t; 
   type_transition cupsd_t tmp_t : file cupsd_tmp_t; 
   type_transition cupsd_t tmp_t : fifo_file cupsd_tmp_t; 

Found 1 named file transition filename_trans:
type_transition cupsd_t tmp_t : file krb5_host_rcache_t "host_0"; 
#

I believe that a type_transition rule for lnk_file:cupsd_tmp_t is missing.
Comment 23 Lukas Vrabec 2019-10-02 08:45:29 UTC 
*** Bug 1756489 has been marked as a duplicate of this bug. ***
Comment 24 Rik Theys 2019-10-21 08:47:28 UTC 
Hi,

Is there any ETA on when an update that fixes this bug will be released for 7.7?

Would you be able to share a .te file that resolves this issue in the mean time? I'm having a hard time finding the correct syntax for configuring the correct type_transition rule...

Regards,
Rik
Comment 25 Rik Theys 2019-10-21 09:27:07 UTC 
Hi,

After some more fiddling I've created the following .te file which seems to work:

====
module esat-cups_tmp 1.0;

require {
        type tmp_t;
        type cupsd_t;
        type cupsd_tmp_t;
        class lnk_file {create read unlink} ;
}

#============= cupsd_t ==============

type_transition cupsd_t tmp_t : lnk_file cupsd_tmp_t;
allow cupsd_t cupsd_tmp_t:lnk_file { create read unlink };
====

I have no idea if these are sufficient.

Regards,
Rik
Comment 27 errata-xmlrpc 2020-03-31 19:10:50 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-2020:1007
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