Overview
By the end of this article you should be able to answer the following questions:
Announcement
I have released my new course on Udemy, Kubernetes By Example. Sign up now to get free lifetime access!$ systemctl status auditd
/var/log/audit/audit.log
$ cat /var/log/audit/audit.log | grep “AVC”
$ sealert -a /var/log/audit/audit.log
$ vim /var/log/messages # search for ‘sealert’
When you are having SELinux access problems one of the first things to investigate are the log files. The auditd service is responsible for writing SELinux logs, so first we need to make sure it is running:
$ systemctl status auditd
auditd.service - Security Auditing Service
Loaded: loaded (/usr/lib/systemd/system/auditd.service; enabled)
Active: active (running) since Sat 2015-06-20 07:20:26 BST; 1 day 3h ago
Main PID: 581 (auditd)
CGroup: /system.slice/auditd.service
├─581 /sbin/auditd -n
├─587 /sbin/audispd
└─589 /usr/sbin/sedispatch
This service will write all SELinux related access denied messages to the /var/log/audit/audit.log file. However this file records lots of other things and not just SELinux related log entries. Therefore we grep for “AVC” to view just SELinux related log entries:
$ cat /var/log/audit/audit.log | grep "AVC"
type=AVC msg=audit(1434247738.386:471): avc: denied { getattr } for pid=1435 comm="httpd" path="/var/www/html/index.html" dev="dm-1" ino=71561345 scontext=system_u:system_r:httpd_t:s0 tcontext=unconfined_u:object_r:admin_home_t:s0 tclass=file
type=AVC msg=audit(1434247738.386:472): avc: denied { getattr } for pid=1435 comm="httpd" path="/var/www/html/index.html" dev="dm-1" ino=71561345 scontext=system_u:system_r:httpd_t:s0 tcontext=unconfined_u:object_r:admin_home_t:s0 tclass=file
type=USER_AVC msg=audit(1434247801.772:476): pid=1 uid=0 auid=4294967295 ses=4294967295 subj=system_u:system_r:init_t:s0 msg='avc: received setenforce notice (enforcing=1) exe="/usr/lib/systemd/systemd" sauid=0 hostname=? addr=? terminal=?'
.
.
This works because all SELinux log entries contains the string “AVC”.
However you can also parse this log file into the sealert utility which will then output the relevant parts of this log in a more human readable format:
$ sealert -a /var/log/audit/audit.log
If after viewing the logs, you are still unsure how to fix this, then you could also looking at the main log file, /var/log/messages, using the “less” command. In main log file, try searching for the keyword sealert. You should then find an entry in the log file that looks something like this:
Jun 21 12:14:20 localhost setroubleshoot: SELinux is preventing /usr/sbin/httpd from read access on the file testfile.html. For complete SELinux messages. run sealert -l d72b5c45-af2d-4a29-95cd-8a7289594b85 Jun 21 12:14:20 localhost python: SELinux is preventing /usr/sbin/httpd from read access on the file testfile.html.
This should hopefully give enough for you to determine what’s wrong. You can also run the sealert command as suggested. So if we run it:
sealert -l d8dfacad-00f5-4796-a00d-c02bbfdc3a41 SELinux is preventing /usr/sbin/httpd from getattr access on the file /var/www/html/testfile.html. ***** Plugin restorecon (99.5 confidence) suggests ************************ If you want to fix the label. /var/www/html/testfile.html default label should be httpd_sys_content_t. Then you can run restorecon. Do # /sbin/restorecon -v /var/www/html/testfile.html ***** Plugin catchall (1.49 confidence) suggests ************************** If you believe that httpd should be allowed getattr access on the testfile.html file by default. Then you should report this as a bug. You can generate a local policy module to allow this access. Do allow this access for now by executing: # grep httpd /var/log/audit/audit.log | audit2allow -M mypol # semodule -i mypol.pp Additional Information: Source Context system_u:system_r:httpd_t:s0 Target Context unconfined_u:object_r:admin_home_t:s0 Target Objects /var/www/html/testfile.html [ file ] Source httpd Source Path /usr/sbin/httpd PortHost localhost.localdomain Source RPM Packages httpd-2.4.6-31.el7.centos.x86_64 Target RPM Packages Policy RPM selinux-policy-3.13.1-23.el7_1.7.noarch Selinux Enabled True Policy Type targeted Enforcing Mode Enforcing Host Name localhost.localdomain Platform Linux localhost.localdomain 3.10.0-229.4.2.el7.x86_64 #1 SMP Wed May 13 10:06:09 UTC 2015 x86_64 x86_64 Alert Count 2 First Seen 2015-06-21 12:14:16 BST Last Seen 2015-06-21 12:45:01 BST Local ID d8dfacad-00f5-4796-a00d-c02bbfdc3a41 Raw Audit Messages type=AVC msg=audit(1434887101.673:2151): avc: denied { getattr } for pid=15563 comm="httpd" path="/var/www/html/testfile.html" dev="dm-1" ino=69211150 scontext=system_u:system_r:httpd_t:s0 tcontext=unconfined_u:object_r:admin_home_t:s0 tclass=file type=SYSCALL msg=audit(1434887101.673:2151): arch=x86_64 syscall=lstat success=no exit=EACCES a0=7f61bd817c68 a1=7fff6a1c4ec0 a2=7fff6a1c4ec0 a3=0 items=0 ppid=1304 pid=15563 auid=4294967295 uid=48 gid=48 euid=48 suid=48 fsuid=48 egid=48 sgid=48 fsgid=48 tty=(none) ses=4294967295 comm=httpd exe=/usr/sbin/httpd subj=system_u:system_r:httpd_t:s0 key=(null) Hash: httpd,httpd_t,admin_home_t,file,getattr
sealert gives a lot of useful info, and it even suggests what command it thinks you need to run that will resolve this issue (with 99.5%) confidence. However as indicated by the confidence level, it’s suggestion might not always be correct.