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I've used the PHP exec command to issue lpr -P printer_name /var/www/html/somefile.pdf but after a RHEL system update (7.2 to 7.3), selinux has decided to start blocking these requests.

selinux permissions of the file being sent to print: 

ls -lZ /var/www/html/somefile.pdf
-rw-r-----. apache webdev system_u:object_r:httpd_sys_rw_content_t:s0 /var/www/html/somefile.pdf

The following appears in the audit log, corresponding with the above exec command from PHP:

time->Thu Nov 3 15:07:02 2016

type=PATH msg=audit(1478200022.446:5151): item=0 name="/etc/cups/lpoptions" inode=134317708 dev=fd:03 mode=0100644 ouid=0 ogid=7 rdev=00:00 obj=system_u:object_r:cupsd_rw_etc_t:s0 objtype=NORMAL

type=CWD msg=audit(1478200022.446:5151): cwd="/var/www/html"

type=SYSCALL msg=audit(1478200022.446:5151): arch=c000003e syscall=2 success=yes exit=5 a0=7fff26837c70 a1=0 a2=0 a3=9 items=1 ppid=19397 pid=46644 auid=4294967295 uid=48 gid=48 euid=48 suid=48 fsuid=48 egid=48 sgid=48 fsgid=48 tty=(none) ses=4294967295 comm="lpr" exe="/usr/bin/lpr.cups" subj=system_u:system_r:httpd_t:s0 key=(null)

type=AVC msg=audit(1478200022.446:5151): avc: denied { open } for pid=46644 comm="lpr" path="/etc/cups/lpoptions" dev="dm-3" ino=134317708 scontext=system_u:system_r:httpd_t:s0 tcontext=system_u:object_r:cupsd_rw_etc_t:s0 tclass=file

type=AVC msg=audit(1478200022.446:5151): avc: denied { read } for pid=46644 comm="lpr" name="lpoptions" dev="dm-3" ino=134317708 scontext=system_u:system_r:httpd_t:s0 tcontext=system_u:object_r:cupsd_rw_etc_t:s0 tclass=file

Getting similar errors with another exec command for wkhtmltopdf.

Here's the current selinux config: 

# getsebool -a | grep httpd
httpd_anon_write --> off
httpd_builtin_scripting --> on
httpd_can_check_spam --> off
httpd_can_connect_ftp --> off
httpd_can_connect_ldap --> off
httpd_can_connect_mythtv --> off
httpd_can_connect_zabbix --> off
httpd_can_network_connect --> on
httpd_can_network_connect_cobbler --> off
httpd_can_network_connect_db --> off
httpd_can_network_memcache --> off
httpd_can_network_relay --> off
httpd_can_sendmail --> on
httpd_dbus_avahi --> off
httpd_dbus_sssd --> off
httpd_dontaudit_search_dirs --> off
httpd_enable_cgi --> on
httpd_enable_ftp_server --> off
httpd_enable_homedirs --> off
httpd_execmem --> off
httpd_graceful_shutdown --> on
httpd_manage_ipa --> off
httpd_mod_auth_ntlm_winbind --> off
httpd_mod_auth_pam --> off
httpd_read_user_content --> off
httpd_run_ipa --> off
httpd_run_preupgrade --> off
httpd_run_stickshift --> off
httpd_serve_cobbler_files --> off
httpd_setrlimit --> off
httpd_ssi_exec --> on
httpd_sys_script_anon_write --> off
httpd_tmp_exec --> off
httpd_tty_comm --> off
httpd_unified --> off
httpd_use_cifs --> off
httpd_use_fusefs --> off
httpd_use_gpg --> off
httpd_use_nfs --> on
httpd_use_openstack --> off
httpd_use_sasl --> off
httpd_verify_dns --> off

All of this started immediately after yum updating my system from RHEL 7.2 to 7.3.

What is causing the denial?

a coder
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    what is the file type are you attempting to print? – cmorrissey Nov 03 '16 at 19:34
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    I am sending a pdf. Ex: `lpr -P printer_name /var/www/html/somefile.pdf`. If I run that on command line as root, the file prints. If I run it via PHP script using the `exec` function.. it fails with the above log data. – a coder Nov 03 '16 at 19:37
  • I suspect your Apache daemon doesn't have the `lpr_exec_t` context applied (there is no single boolean for this, unlike eg sendmail). The quickest (least safe) fix may be `sudo semanage permissive -a lpr_t`. See also [this post](http://danwalsh.livejournal.com/55324.html) for gory details (and how to apply contexts). – bishop Nov 03 '16 at 19:38
  • I've added getsebool output to the question. – a coder Nov 03 '16 at 19:38
  • @bishop, not sure that will help since selinux is now also blocking everything I issue over php's `exec` function. – a coder Nov 03 '16 at 19:51

1 Answers1

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I ended up installing some additional seLinux tools to help troubleshoot: 

yum install setroubleshoot setools

Then ran

sealert -a /var/log/audit/audit.log

The output suggested the following modifications: 

ausearch -c 'lpr' --raw | audit2allow -M my-lpr
semodule -i my-lpr.pp
ausearch -c 'wkhtmltopdf-amd' --raw | audit2allow -M my-wkhtmltopdfamd
semodule -i my-wkhtmltopdfamd.pp

Issued those commands and am now able to print from my PHP app again.

a coder
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